Aktivitas Listrik Jantung
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Aktivitas Listrik Jantung Untuk dapat memompa darah, jantung harus berkontraksi yang dicetuskan oleh potensial aksi yang menyebar melalui membran sel sel otot. Jantung berkontraksi secara berirama akibat potensial aksi yang ditimbulkannya sendiri, disebut sebagai otoritmisitas. Terdapat dua jenis sel otot jantung : 1 Sel kontraktil(99 %) merupakan sel yang memiliki fungsi mekanik (memompa darah), dalam keadaan normal tidak dapat menghasilkan sendiri potensial aksinya 2 Sel otoritmikberfungsi mencetuskan dan menghantarkan potensial aksi yang bertanggung jawab untuk kontraksi sel sel pekerja. Sel otoritmik ini dapat ditemukan di lokasi lokasi berikut : Nodus sinoatrium (SA), daerah kecil khusus di dinding atrium kanan dekat muara vena cava superior Nodus atrioventrikel (AV), terletak di dasar atrium kanan dekat septum, tepat di atas hubungan antara atrium dan ventrikel Berkas His (berkas atrioventrikel), suatu jaras sel sel khusus yang berasal dari nodus AV dan masuk ke septum interventrikular. Pada septum interventrikular jaras ini bercabang dua (kanan dan kiri), kemudian berjalan ke bawah melalui septum, melingkari ujung ventrikel dan kembali ke atrium di sepanjang dinding luar. Serat Purkinje,merupakan serat terminal halus yang berjalan dari berkas His dan menyebar ke seluruh miokardium ventrikel.
Sel sel otoritmik jantung tidak memiliki potensial istirahat melainkan mereka memiliki aktivitas pacemaker yaitu depolarisasi yang terjadi secara perlahan pada membrane sel sel tersebut hingga mencapai ambang dan kemudian menimbulkan potensial aksi. Penyebab terjadinya depolarisasi ini diperkirakan sebagai akibat dari : 1.Arus keluar K+ yang berkurang diirngi dengan arus masuk Na+ yang konstan Permeabilitas membrane terhadap K+ menurun antara potensial potensial aksi, karena saluran K+ diinaktifkan sehingga aliran keluar ion positif menurun. Sementara itu, influks pasif Na+ dalam jumlah kecil tidak berubah akibatnya bagian dalam membrane menjadi lebih positif dan secara bertahap mengalami depolarisasi hingga mencapai ambang. 2.Peningkatan arus masuk Ca2+ Setelah mencapai ambang dan saluran Ca2+ terbuka, terjadi influks Ca2+ secara cepat menimbulkan fase naik dari potensial aksi spontan. Sel sel otoritmik berbeda kecepatannya untuk menghasilkan potensial aksi karena terdapat perbedaan kecepatan depolarisasi. Sel sel jantung yang terletak di nodus SA memiliki kecepatan pembentukan potensial aksi tertinggi. Sekali potensial aksi timbul di salah satu sel otot jantung, potensial aksi tersebut akan menyebar ke seluruh miokardium melalui gap junction dan penghantar khusus.
Penjalaran Impuls Jantung ke Seluruh Jantung potensial aksi dimulai di nodus SA kemudian menyebar ke seluruh jantung. Agar jantung berfungsi secara efisien, penyebaran eksitasi harus memenuhi 3 kriteria : 3 Eksitasi dan kontraksi atrium harus selesai sebelum kontraksi ventrikel dimulai. 4 Eksitasi serat serat otot jantung harus dikoordinasi untuk memastikan bahwa setiap bilik jantung berkontraksi sebagai suatu kesatuan untuk menghasilkan daya pompa yang efisien.Apabila serat serat otot di bilik jantung tereksitasi dan berkontraksi secara acak, tidak simultan dan terkoordinasi (fibrilasi) maka darah tidak akan dapat terpompa. 5 Pasangan atrium dan pasangan ventrikel harus secara fungsional terkoordinasi, sehingga kedua pasangan tersebut berkontaksi secara simultan. Hal ini memungkinkan darah terpompa ke sirkulasi paru dan sistemik Eksitasi atrium.Suatu potensial aksi yang berasal dari nodus SA pertama kali menyebar ke kedua atrium, terutama dari sel ke sel melalui gap junction. Selain itu, terdapat jalur penghantar khusus yang mempercepat penghantaran impuls dari atrium, yaitu : Jalur antaratrium, berjalan dari nodus SA di atrium kanan ke atrium kiri. Jalur antarnodus, berjalan dari nodus SA ke nodus AV. Karena atrium dan ventrikel dihubungkan oleh jaringan ikat yang tidak menghantarkan listrik, maka satu satunya cara agar potensial aksi dapat menyebar ke ventrikel adalah dengan melewati nodus AV. Transmisi antara Atrium dan Ventrikel. Potensial aksi dihantarkan relative lebih lambat melalui nodus AV. Kelambanan ini memberikan waktu untuk memungkinkan atrium mengalami depolarisasi sempurna dan berkontraksi sebelum depolarisasi dan kontraksi ventrikel terjadi. Hal ini bertujuan agar ventrikel dapat terisi sempurna. Eksitasi ventrikel.Setelah perlambatan itu, kemudian impuls dengan cepat berjalan melalui berkas His dan ke seluruh miokardium ventrikel melalui serat serat purkinje. Sistem penghantar ventrikel lebih terorganisasi dan lebih penting daripada jalur antaratrium dan antarnodus, karena massa ventrikel jauh lebih besar daripada massa atrium. Potensial Aksi Pada Sel Kontraktil Otot Jantung Potensial aksi yang terjadi pada sel kontraktil otot jantung memperlihatkan fase datar (plateu) yang khas. Pada saat membran mengalami eksitasi, terjadi perubahan gradien membran secara cepat akibat masuknya Na+. Membran pun mengalami potensial aksi. Segera setelah potensial aksi dicapai, permeabilitas membran terhadap Na+ berkurang. Namun uniknya, membran potensial dipertahankan selama beberapa ratus milidetik sehingga menghasilkan fase datar (plateu) potensial aksi.Perubahan voltase yang mendadak selama fase naik menuju potensial aksi menimbulkan 2 perubahan yang turut serta mempertahankan fase datar tersebut, yaitu pengaktifan slow L-type Ca2+ channel dan penurunan permeabilitas K+. Pembukaan Ca2+ channel menyebabkan influks Ca2+ yang bermuatan positif. Penurunan aliran K+ mencegah repolarisasi cepat membran sehingga mempertahankan fase datar. Fase turun potensial aksi yang berlangsung cepat terjadi akibat inaktivasi Ca2+ channel dan peningkatan permeabilitas K+. Mekanisme dasar terjadinya kontraksi sel miokardium apabila terdapat potensial aksi serupa dengan proses eksitasi-kontraksi otot rangka. Bedanya, selama potensial aksi sel miokardium berlangsung, sejumlah besar ion Ca akan berdifusi dari ekstrasel ke sitosol, menembus membran plasma untuk mempertahankan potensial aksi sel miokardium, melewati T-tubule dan memicu terbukanya kanal ion Ca dari lateral sacs retikulum sarkoplasma memperpanjang masa kontraksi cukup waktu untuk memompa darah. Peran Ca2+ di sitosol adalah untuk berikatan dengan kompleks troponin-tropomiosin sehingga memungkinkan terjadinya kontraksi. Siklus Jantung Siklus jantung adalah periode dimulainya satu denyutan jantung dan awal dari denyutan selanjutnya. Setiap siklus dimulai oleh pembentukan potensial aksi yang spontan di nodus sinus. Siklus jantung terdiri dari periode sistol dan diastol. Sistol adalah periode kontraksi dari ventrikel, dimana darah akan dikeluarkan dari jantung. Diastol adalah periode relaksasi dari ventrikel, dimana terjadi pengisian darah. Diastol dapat dibagi menjadi dua proses yaitu relaksasi isovolumetrik dan ventricular filling. Pada relaksasi isovolumetrik terjadi ventrikel yang mulai relaksaasi, katup semilunar dan katup
atrioventrikularis tertutup dan volume ventrikel tetap tidak berubah. Pada ventricular filling dimana tekanan dari atrium lebih tinggi dari tekanan di ventrikel, katup mitral dan katup trikuspid akan terbuka sehingga ventrikel akan terisi 80% dan akan mencapai 100 % jika atrium berkontraksi. Volume total yang masuk ke dalam diastol disebut End Diastolic Volume. Sistolik dapat dibagi menjadi dua proses yaitu kontraksi isovolumetrik dan ejeksi ventrikel. Pada kontraksi isovolumetrik, kontraksi sudah dimulai tetapi katup katup tetap tertutup. Tekanan juga telah dihasilkan tetapi tidak dijumpai adanya pemendekan dari otot. Pada ejeksi ventrikel , tekanan dalam ventrikel lebih tinggi dibandingkan dengan tekanan pada aorta dan pulmoner sehingga katup aorta dan katup pulmoner terbuka dan akhirnya darah akan dipompa ke seluruh tubuh. Pada saat ini terjadi pemendekan dari otot. Sisa darah yang terdapat di ventrikel disebut End Systolic Volume. Cardiac Output.Merupakan volume darah yang dipompa oleh setiap ventrikel per menitnya. CO dari setiap ventrikel secara normal sama, walaupun terdapat sedikit variasi. Penentu utama CO adalah detak jantung dan stroke volume (= Volume darah yang dikeluarkan masing-masing ventrikel). Jika dalam keadaan istirahat, detak jantung = 70 x/menit dan SV = 70 ml/detak, maka: Cardiac Output= Detak jantung x SV. Dalam keadaan istirahat, curah jantung (cardiac output) dapat mencapai 5 L per menit. Saat berolahraga, curah jantung yang dihasilkan dapat mencapai sekitar 20-25 L per menit. Selisih antara curah jantung saat istirahat dengan curah jantung maksimal disebut cardiac reserve. faktor yang mempengaruhi CO : Heart Rate (detak Jantung).Dalam keadaan normal nodus SA merupakan pacemaker jantung dan mengatur HR. Karena nodus SA ini dipersarafi oleh Saraf otonom (simpatis dan parasimpatis) maka secara tidak langsung HR juga dipengaruhi oleh saraf otonom. Stroke Volume.Diatur oleh dua factor , yaitu intrinsic (aliran vena) dan ekstrinsik (stimulasi simpatik). Factor intrinsic diatur oleh mekanisme hukum Franks Starling pada jantung. Semakin banyak aliran vena yang masuk ke dalam jantung semakin besar pula volume diastole akhir dan jantung menjadi semaikn tertarik dan melebar. Karena keadaan otot jantung yang semakin panjang sebelum kontraksi ini, maka semakin kuat pula kontraksinya.
CaldesmonFrom Wikipedia, the free encyclopedia Caldesmon is a protein that in humans is encoded by the CALD1 gene. Caldesmon is a calmodulin binding protein. Like calponin, caldesmon tonically inhibits the ATPase activity of myosin in smooth muscle. This gene encodes a calmodulin- and actin-binding protein that plays an essential role in the regulation of smooth muscle and nonmuscle contraction. The conserved domain of this protein possesses the binding activities to Ca++-calmodulin, actin, tropomyosin, myosin, and phospholipids. This protein is a potent inhibitor of the actin-tropomyosin activated myosin MgATPase, and serves as a mediating factor for Ca++-dependent inhibition of smooth muscle contraction. Alternative splicing of this gene results in multiple transcript variants encoding distinct isoforms.
CalponinCalponin is a calcium binding protein. Calponin tonically inhibits the ATPase activity of myosin in smooth muscle. Phosphorylation of calponin by a protein kinase, which is dependent upon calcium binding to calmodulin, releases the calponin's inhibition of the smooth muscle ATPase.
Structure and functionCalponin is mainly made up of -helices with hydrogen bond turns. It is a binding protein and is made up of three domains. These domains in order of appearance are Calponin Homology (CH), regulatory domain (RD), and Click-23, domain that contains the calponin repeats. At the CH domain calponin binds to -actin and filamin and binds to actin within the RD domain. Calponin does
not bind to actin in the CH domain as generally described due to the fact that the CH domain is known to bind calcium to calmodulin which then inhibits actin binding. Calponin is responsible for binding many actin binding proteins, phospholipids, and regulates the actin/myosin interaction. Calponin is also thought to negatively affect the bone making process due to being expressed in high amounts in osteoblasts.
DesminFrom Wikipedia, the free encyclopedia Jump to: navigation, search Desmin is a protein that in humans is encoded by the DES gene. Desmin is a type III intermediate filament found near the Z line in sarcomeres. It was first described in 1976, first purified in 1977, the gene was cloned in 1989, and the first knockout mouse was created in 1996. Desmin is only expressed in vertebrates, however homologous proteins are found in many organisms. It is a 52kD protein that is a subunit of intermediate filaments in skeletal muscle tissue, smooth muscle tissue, and cardiac muscle tissue.
Putative functionsThe function of desmin has been deduced through studies in knockout mice, but the underlying mechanism of its action is not known. These possibilities may be the result of interactions with other proteins and not desmin itself. More research needs to be done on desmin's expression and interactions in the muscle cell in order to determine its exact function. Desmin is one of the earliest protein markers for muscle tissue in embryogenesis as it is detected in the somites of myoblasts. Although it is present early in the development of muscle cells it is expressed at low levels and increases as the cell nears terminal differentiation the muscle cell matures only desmin is present. A similar protein, vimentin, is present in higher amounts during embryogenesis while desmin is present in higher amounts after differentiation. This suggests that there may be some interaction between the two in determining muscle cell differentiation. However desmin knockout mice develop normally and only experience defects later in life. Since desmin is expressed at a low level during differentiation another protein may be able to compensate for desmin's function early in development but not later on. Desmin is also important in muscle cell architecture and structure since it connects many components of the cytoplasm. The sarcomere is a component of muscle cells composed of actin and myosin motor proteins which allow the cell to contract. Desmin forms a scaffold around the Z-disk of the sarcomere and connects the Z-disk to the subsarcolemmal cytoskeleton (the cytoplasmic part of the muscle cell plasma membrane). It links the myofibrils laterally by connecting the Zdisks. Through its connection to the sarcomere Desmin connects the contractile apparatus to the cell nucleus, mitochondria, and post-synaptic areas of motor endplates. These connections maintain the structural and mechanical integrity of the cell during contraction while also helping in force transmission and longitudinal load bearing. There is some evidence that desmin may also connect the sarcomere to the extracellular matrix (ECM) through desmosomes which could be important in signalling between the ECM and the sarcomere which could regulate muscle contraction and movement. Finally, desmin may be important in mitochondria function. When desmin is not functioning properly there is improper mitochondrial distribution, number, morphology and function. Since desmin links the mitochondria to the sarcomere it may transmit information about contractions and energy need and through this regulate the aerobic respiration rate of the muscle cell.
Knockout phenotypeWhen the gene for desmin is knocked out it is no longer able to function properly. Mice with the desmin knockout gene develop normally and are fertile, however soon after birth they begin to show defects in skeletal, smooth and cardiac muscle; in particular the diaphragm and heart are affected.  The mice without desmin are weaker and fatigue more easily than wild type mice  but the muscle fibers are less likely to be damaged during contraction  Mice without desmin also have impaired mitochondrial function.
Associated diseasesMain article: Desmin-related myofibrillar myopathy Desmin-related myopathy (DRM or Desminopathy) is a subgroup of the myofibrillar myopathy diseases and is the result of a mutation in the gene that codes for desmin which prevents it from forming protein filaments, instead forming aggregates of desmin and other proteins throughout the cell. It is also associated with Sarcoma botryoides (rhabdomyosarcoma variant) - a spindle-shaped vaginal carcinoma that affects girls < 4 years of age.
StructureThere are three major domains to this protein: a conserved alpha helix rod, a variable non alpha helix head, and a carboxy-terminal tail. Desmin, as all intermediate filaments, shows no polarity when assembled. The rod domain consists of 308 amino acids with parallel alpha helical coiled coil dimers and three linkers to disrupt it. The rod connects to the head domain. The head domain 84 amino acids with many arginine, serine, and aromatic residues is important in filament assembly and dimer-dimer interactions. The tail domain is responsible for the integration of filaments and interaction with proteins and organelles.
CalmodulinFrom Wikipedia, the free encyclopedia Jump to: navigation, search
Calmodulin 3D structure Calmodulin (CaM) (an abbreviation for CALcium-MODULated proteIN) is a calcium-binding messenger protein expressed in all eukaryotic cells. CaM is a multifunctional intermediate
messenger protein that transduces calcium signals by binding calcium ions and then modifying its interactions with various target proteins.
FunctionCaM mediates many crucial processes such as inflammation, metabolism, apoptosis, smooth muscle contraction, intracellular movement, short-term and long-term memory, and the immune response. CaM is expressed in many cell types and can have different subcellular locations, including the cytoplasm, within organelles, or associated with the plasma or organelle membranes. Many of the proteins that CaM binds are unable to bind calcium themselves, and use CaM as a calcium sensor and signal transducer. CaM can also make use of the calcium stores in the endoplasmic reticulum, and the sarcoplasmic reticulum. CaM can undergo posttranslational modifications, such as phosphorylation, acetylation, methylation and proteolytic cleavage, each of which has potential to modulate its actions.
StructureCalmodulin is a small, highly conserved protein approximately 148 amino acids long (16706 Daltons). It contains four EF-hand motifs, each of which binds a Ca2+ ion. The protein has two approximately symmetrical globular domains (the N- and C-domain), separated by a flexible linker region. Calcium participates in an intracellular signalling system by acting as a diffusible second messenger to the initial stimuli.
MechanismUp to four calcium ions are bound by calmodulin via its four EF hand motifs. EF hands supply an electronegative environment for ion coordination. After calcium binding, hydrophobic methyl groups from methionine residues become exposed on the protein via conformational change. This presents hydrophobic surfaces, which can in turn bind to Basic Amphiphilic Helices (BAA helices) on the target protein. These helices contain complementary hydrophobic regions. The flexibility of Calmodulin's hinged region allows the molecule to "wrap around" its target. This property allows it to tightly bind to a wide range of different target proteins.
Dynamic featuresCompared to the X-ray crystal structure, the C-terminal domain solution structure is similar while the EF hands of the N-terminal domain are considerably less open. The backbone flexibility within calmodulin is key to its ability to bind a wide range of targets.
Other calcium-binding proteinsCalmodulin belongs to one of the two main groups of calcium-binding proteins, called EF hand proteins. The other group, called annexins, bind calcium and phospholipid (e.g., lipocortin). Many other proteins bind calcium, although binding calcium may not be considered their principal function in the cell.
AKTFrom Wikipedia, the free encyclopedia (Redirected from Protein Kinase B)
Akt, also known as Protein Kinase B (PKB), is a serine/threonine-specific protein kinase that plays a key role in multiple cellular processes such as glucose metabolism, apoptosis, cell proliferation, transcription and cell migration.
Family membersAkt1 is involved in cellular survival pathways, by inhibiting apoptotic processes. Akt1 is also able to induce protein synthesis pathways, and is therefore a key signaling protein in the cellular pathways that lead to skeletal muscle hypertrophy, and general tissue growth. Since it can block apoptosis, and thereby promote cell survival, Akt1 has been implicated as a major factor in many types of cancer. Akt (now also called Akt1) was originally identified as the oncogene in the transforming retrovirus, AKT8. Akt2 is an important signaling molecule in the Insulin signaling pathway. It is required to induce glucose transport. In a mouse which is null for Akt1 but normal for Akt2, glucose homeostasis is unperturbed, but the animals are smaller, consistent with a role for Akt1 in growth. In contrast, mice which do not have Akt2, but have normal Akt1, have mild growth deficiency and display a diabetic phenotype (insulin resistance), again consistent with the idea that Akt2 is more specific for the insulin receptor signaling pathway. The role of Akt3 is less clear, though it appears to be predominantly expressed in the brain. It has been reported that mice lacking Akt3 have small brains.
NameThe name Akt does not refer to its function. The "Ak" in Akt was a temporary classification name for a mouse strain originally bred and maintained by Jacob Furth that developed spontaneous thymic lymphomas. The "t" stands for 'thymoma'; the letter was added when a transforming retrovirus was isolated from the Ak strain, which was termed "Akt-8". When the oncogene encoded in this virus was discovered, it was termed v-Akt. Thus, the later identified human analogues were named accordingly.
RegulationAkt is involved in the PI3K/AKT/mTOR pathway and other signaling pathways.
Binding phospholipidsAkt possesses a protein domain known as a PH domain, or Pleckstrin Homology domain, named after Pleckstrin, the protein in which it was first discovered. This domain binds to phosphoinositides with high affinity. In the case of the PH domain of Akt, it binds either PIP3 (phosphatidylinositol (3,4,5)-trisphosphate, PtdIns(3,4,5)P3) or PIP2 (phosphatidylinositol (3,4)-bisphosphate, PtdIns(3,4)P2). This is useful for control of cellular signaling because the di-phosphorylated phosphoinositide PIP2 is only phosphorylated by the family of enzymes, PI 3kinases (phosphoinositide 3-kinase or PI3-K), and only upon receipt of chemical messengers which tell the cell to begin the growth process. For example, PI 3-kinases may be activated by a G protein coupled receptor or receptor tyrosine kinase such as the insulin receptor. Once activated, PI 3-kinase phosphorylates PIP2 to form PIP3.
PhosphorylationOnce correctly positioned at the membrane via binding of PIP3, Akt can then be phosphorylated by its activating kinases, phosphoinositide dependent kinase 1 (PDPK1 at threonine 308) and
mTORC2 (at serine 473). First, the mammalian target of rapamycin complex 2(mTORC2); mTORC2 therefore functionally acts as the long-sought PDK2 molecule, although other molecules, including Integrin-linked kinase (ILK) and Mitogen-Activated Protein Kinase Activated Protein Kinase-2 (MAPKAPK2) can also serve as PDK2. Phosphorylation by mTORC2 stimulates the subsequent phosphorylation of Akt by PDPK1. Activated Akt can then go on to activate or deactivate its myriad substrates (e.g. mTOR) via its kinase activity. Besides being a downstream effector of PI 3-kinases, Akt may possibly also be activated in a PI 3kinase-independent manner. Studies have suggested that cAMP-elevating agents could activate Akt through protein kinase A (PKA) in the presence of insulin, although these studies are disputed and the mechanism of action is unclear.
Lipid phosphatases and PIP3PI3K dependent Akt activation can be regulated through the tumor suppressor PTEN, which works essentially as the opposite of PI3K mentioned above. PTEN acts as a phosphatase to dephosphorylate PtdIns(3,4,5)P3 back to PtdIns(4,5)P2. This removes the membranelocalization factor from the Akt signaling pathway. Without this localization, the rate of Akt activation decreases significantly, as do all of the downstream pathways that depend on Akt for activation. PIP3 can also be de-phosphorylated at the "5" position by the SHIP family of inositol phosphatases, SHIP1 and SHIP2. These poly-phosphate inositil phosphatases dephosphorylate PtdIns(3,4,5)P3 to form PtdIns(3,4)P2.
Protein phosphatasesThe phosphatases in the PHLPP family, PHLPP1 and PHLPP2 have been shown to directly de-phosphorylate, and therefore inactivate, distinct Akt isoforms. PHLPP2 dephosphorylates Akt1 and Akt3, whereas PHLPP1 is specific for Akt 2 and Akt3.
FunctionAkt regulates cellular survival and metabolism by binding and regulating many downstream effectors, e.g. Nuclear Factor-B, Bcl-2 family proteins and murine double minute 2 (MDM2).
Overview of signal transduction pathways involved in apoptosis. Akt could promote growth factor-mediated cell survival both directly and indirectly. BAD is a pro-
apoptotic protein of the Bcl-2 family. Akt could phosphorylate BAD on Ser136, which makes BAD dissociate from the Bcl-2/Bcl-X complex and lose the pro-apoptotic function. Akt could also activate NF-B via regulating IB kinase (IKK), thus result in transcription of pro-survival genes.
Cell CycleAkt is known to play a role in the cell cycle. Under various circumstances, activation of Akt was shown to overcome cell cycle arrest in G1 and G2 phases. Moreover, activated Akt may enable proliferation and survival of cells that have sustained a potentially mutagenic impact and, therefore, may contribute to acquisition of mutations in other genes.
MetabolismAkt2 is required for the insulin-induced translocation of glucose transporter 4 (GLUT4) to the plasma membrane. Glycogen synthase kinase 3 (GSK-3) could be inhibited upon phosphorylation by Akt, which results in increase of glycogen synthesis. GSK3 is also involved in Wnt signaling cascade, so Akt might be also implicated in the Wnt pathway. Still unknown role in HCV induced steatosis.
AngiogenesisAkt1 has also been implicated in angiogenesis and tumor development. Although deficiency of Akt1 in mice inhibited physiological angiogenesis, it enhanced pathological angiogenesis and tumor growth associated with matrix abnormalities in skin and blood vessels.
Ras subfamilyFrom Wikipedia, the free encyclopedia (Redirected from Ras protein) Jump to: navigation, search This article is about the p21/Ras protein. For the p21/waf1 protein see p21.
H-Rasstructure PDB 121p, surface colored by conservation in Pfam seed alignment: gold,most conserved; dark cyan, least conserved. Identifiers
cd04138 [show]Available protein structures: Ras is the name given to a family of related proteins found inside cells, including human cells. All Ras protein family members belong to a class of protein called small GTPase, and are involved in transmitting signals within cells (cellular signal transduction). Ras is the prototypical member of the Ras superfamily of proteins, which are all related in 3D structure and regulate diverse cell behaviours. The name 'Ras' is an abbreviation of 'Rat sarcoma', reflecting the way the first members of the protein family were discovered. The name ras is also used to refer to the family of genes encoding those proteins. When Ras is 'switched on' by incoming signals, it subsequently switches on other proteins, which ultimately turn on genes involved in cell growth, differentiation and survival. As a result, mutations in ras genes can lead to the production of permanently activated Ras proteins. This can cause unintended and overactive signalling inside the cell, even in the absence of incoming signals. Because these signals result in cell growth and division, overactive Ras signaling can ultimately lead to cancer. Ras is the most common oncogene in human cancer - mutations that permanently activate Ras are found in 20-25% of all human tumors and up to 90% in certain types of cancer (e.g. pancreatic cancer). For this reason, Ras inhibitors are being studied as a treatment for cancer, and other diseases with Ras overexpression.
Pfam InterPro PROSITE SCOP SUPERFA MILY OPM protein CDD
PF00071 IPR013753 PDOC00017 5p21 5p21 1uad
Contents1 History 2 Structure 3 Function o 3.1 Activation and deactivation o 3.2 Membrane attachment 4 Members 5 Ras in cancer o 5.1 Inappropriate activation o 5.2 Constitutively active Ras o 5.3 Ras-targeted cancer treatments
6 References 7 External links
HistoryThe first two ras genes, HRAS and KRAS, were first identified from studies of two cancercausing viruses, the Harvey sarcoma virus and Kirsten sarcoma virus, by Edward M. Scolnick and colleagues at the National Institutes of Health (NIH). These viruses were discovered originally in rats during the 1960s by Jennifer Harvey and Werner Kirsten, respectively, hence the name Rat sarcoma. In 1982, activated and transforming human ras genes were discovered in human cancer cells by Geoffrey M. Cooper at Harvard, Mariano Barbacid and Stuart A. Aaronson at the NIH and by Robert Weinberg of MIT. A third ras gene was subsequently discovered   by researchers at the Institute of Cancer Research, funded by the Cancer Research Campaign (now Cancer Research UK), and named NRAS, for its initial identification in human neuroblastoma cells. The three human ras genes encode extremely similar proteins made up of chains of 188 to 189 amino acids, designated H-Ras, N-Ras and K-Ras4A and K-Ras4B (the two K-Ras proteins arise from alternative splicing).
H-Rasstructure PDB 121p, ribbon showing strands in purple, helices in aqua, loops in gray. Alsoshown are the bound GTP analog and magnesium ion. This section may require cleanup to meet Wikipedia's quality standards. No cleanup reason has been specified. Please help improve this section if you can. (April 2009) Ras contains a six-stranded beta sheet and 5 alpha helices: G domain (166 amino acids) which binds guanosine nucleotides, about 20kDa. C terminal membrane targeting region (CAAX-COOH, also known as CAAX box) which is lipid-modified by farnesyl transferase, RCE1 and ICMT The G domain contains five G motifs that bind GDP/GTP directly G1 - P-loop binds the beta phosphate of GDP and GTP G2 - threonine-35 also switch 1, binds the terminal phosphate of GTP, but makes no contacts with GDP
G3 - DXXG motif, aspartate-57 is specific for guanine rather than adenine G4 - LVGNKxDL motif G5 - SAK consensus sequence, the alanine-146 is specific for guanine rather than adenine and two switches which are the main parts of the protein that move upon activation by GTP. switch I includes threonine-35 switch II glycine-60 in DXXG motif Ras also binds a magnesium ion which helps to coordinate nucleotide binding.
Overview of signal transduction pathways involved in apoptosis. Ras proteins function as binary molecular switches that control intracellular signaling networks. Rasregulated signal pathways control such processes as actin cytoskeletal integrity, proliferation, differentiation, cell adhesion, apoptosis, and cell migration. Ras and ras-related proteins are often deregulated in cancers, leading to increased invasion and metastasis, and decreased apoptosis. This section requires expansion. (April 2009) Ras activates several pathways, of which the mitogen-activated protein (MAP) kinase cascade has been well-studied. This cascade transmits signals downstream and results in the transcription of genes involved in cell growth and division. There is a separate AKT pathway that inhibits apoptosis.
Activation and deactivationRas is a G protein, or a guanosine-nucleotide-binding protein. Specifically, it is a singlesubunit small GTPase, which is related in structure to the G subunit of heterotrimeric G proteins (large GTPases). G proteins function as binary signaling switches with "on" and "off" states. In the "off" state it is bound to the nucleotide guanosine diphosphate (GDP), while in the "on" state, Ras is bound to guanosine triphosphate (GTP), which has an extra phosphate group as compared to GDP. This extra phosphate holds the two switch regions in a "loaded-spring" configuration (specifically the Thr-35 and Gly-60). When released, the switch regions relax which causes a conformational change into the inactivate state. Hence, activation and deactivation of Ras and other small G proteins are controlled by cycling between the active GTP-bound and inactive GDP-bound forms.
The process of exchanging the bound nucleotide is facilitated by guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs). As per its classification, Ras has an intrinsic GTPase activity, which means that the protein on its own will hydrolyze a bound GTP molecule into GDP. However this process is too slow for efficient function, and hence the GAP for Ras, RasGAP, may bind to and stabilize the catalytic machinery of Ras, supplying additional catalytic residues ("arginine finger") such that a water molecule is optimally positioned for nucleophilic attack on the gamma-phosphate of GTP. An inorganic phosphate is released and the Ras molecule is now bound to a GDP. Since the GDP-bound form is "off" or "inactive" for signaling, GTPase Activating Protein inactivates Ras by activating its GTPase activity. Thus, GAPs accelerate Ras inactivation. GEFs catalyze a "push and pull" reaction which releases GDP from Ras. They insert close to the Ploop and magnesium cation binding site and inhibit the interaction of these with the gamma phosphate anion. Acidic (negative) residues in switch II "pull" a lysine in the P-loop away from the GDP which "pushes" switch I away from the guanine. The contacts holding GDP in place are broken and it is released into the cytoplasm. Because intracellular GTP is abundant relative to GDP (approximately 10 fold more) GTP predominantly re-enters the nucleotide binding pocket of Ras and reloads the spring. Thus GEFs facilitate Ras activation. Well known GEFs include Son of Sevenless (Sos) and cdc25 which include the RasGEF domain. The balance between GEF and GAP activity determines the guanine nucleotide status of Ras, thereby regulating Ras activity. In the GTP-bound conformation, Ras has high affinity for numerous effectors which allow it to carry out its functions. These include PI3K. Other small GTPases may bind adaptors such as arfaptin or second messenger systems such as adenylyl cyclase. The Ras binding domain is found in many effectors and invariably binds to one of the switch regions, because these change conformation between the active and inactive forms. However, they may also bind to the rest of the protein surface. Other proteins exist which may augment the activity of Ras family proteins. One example is GDI (GDP Disassociation Inhibitor); These function by slowing the exchange of GDP for GTP and thus, prolonging the inactive state of Ras family members. Other proteins that further augment this cycle may exist.
Membrane attachmentRas is attached to the cell membrane owing to its prenylation and palmitoylation (HRAS and NRAS) or the combination of prenylation and a polybasic sequence adjacent to the prenylation site (KRAS). The C-terminal CaaX box of Ras first gets farnesylated at its Cys residue in the cytosol, allowing Ras to loosely insert into the membrane of the endoplasmatic reticulum and other cellular membranes. The Tripeptide (aaX) is then cleaved from the C-terminus by a specific prenyl-protein specific endoprotease and the new C-terminus is methylated by a methyltransferase. K-Ras procession is completed at this stage. Dynamic electrostatic interactions between its positively charged basic sequence with negative charges at the inner leaflet of the plasma membrane account for its predominant localization at the cell surface at steady-state. NRAS and HRAS are further processed on the surface of the Golgi apparatus by palmitoylation of one or two Cys residues, respectively, adjacent to the CaaX box. The proteins thereby become stably membrane anchored and are transported to the plasma membrane on vesicles of the secretory pathway. Depalmitoylation eventually releases the proteins from the membrane, allowing them to enter another cycle of palmitoylation and depalmitoylation. This cycle is believed to prevent the leakage of NRAS and HRAS to other membranes over time and to maintain their steady-state localization along the Golgi apparatus, secretory pathway, plasma membrane and inter-
linked endocytosis pathway.
Ras in cancerMutations in the Ras family of proto-oncogenes (comprising H-Ras, N-Ras and K-Ras) are very common, being found in 20% to 30% of all human tumours. it is reasonable to speculate that a pharmacological approach that curtails Ras activity may represent a possible method to inhibit certain cancer types. Ras point mutations are the single most common abnormality of human protooncogenes. Ras inhibitor trans-farnesylthiosalicylic acid (FTS, Salirasib) exhibits profound anti-oncogenic effects in many cancer cell lines.
Inappropriate activationInappropriate activation of the gene has been shown to play a key role in signal transduction, proliferation and malignant transformation. Mutations in a number of different genes as well as RAS itself can have this effect. Oncogenes such as p210BCR-ABL or the growth receptor erbB are upstream of Ras, so if they are constitutively activated their signals will transduce through Ras. The tumour suppressor gene NF1 encodes a Ras-GAP its mutation in neurofibromatosis will mean that Ras is less likely to be inactivated. Ras can also be amplified, although this only occurs occasionally in tumours. Finally, Ras oncogenes can be activated by point mutations so that the GTPase reaction can no longer be stimulated by GAP this increases the half life of active Ras-GTP mutants.
Constitutively active RasConstitutively active Ras (RasD) is one which contains mutations that prevent GTP hydrolysis, thus locking Ras in a permanently 'On' state. The most common mutations are found at residue G12 in the P-loop and the catalytic residue Q61. The glycine to valine mutation at residue 12 renders the GTPase domain of Ras insensitive to inactivation by GAP and thus stuck in the "on state". Ras requires a GAP for inactivation as it is a relatively poor catalyst on its own, as opposed to other G-domain-containing proteins such as the alpha subunit of heterotrimeric G proteins. Residue 61is responsible for stabilizing the transition state for GTP hydrolysis. Because enzyme catalysis in general is achieved by lowering the energy barrier between substrate and product, mutation of Q61 to K necessarily reduces the rate of intrinsic Ras GTP hydrolysis to physiologically meaningless levels. See also "dominant negative" mutants such as S17N and D119N.
Ras-targeted cancer treatmentsReovirus was noted to be a potential cancer therapeutic when early studies on reovirus suggested it reproduces well in certain cancer cell lines. It has since been shown to replicate specifically in cells that have an activated Ras pathway (a cellular signaling pathway that is involved in cell growth and differentiation). Reovirus replicates in and eventually kills Ras-activated tumour cells and as cell death occurs, progeny virus particles are free to infect surrounding cancer cells. This cycle of infection, replication and cell death is believed to be repeated until all tumour cells carrying an activated Ras pathway are destroyed. Activating mutations of the Ras protein and upstream elements of the Ras protein may play a role in more than two thirds of all human cancers, including most metastatic disease. Reolysin, a formulation of reovirus, is currently in clinical trials for the treatment of various cancers.
Glucose transporterGlucose transporters are a wide group of membrane proteins that facilitate the transport of glucose over a plasma membrane. Because glucose is a vital source of energy for all life these transporters are present in all phyla. The GLUT or SLC2A family are a protein family that is found in most mammalian cells.
Synthesis of free glucoseMost non-autotrophic cells are unable to produce free glucose because they lack expression of glucose-6-phosphatase and, thus, are involved only in glucose uptake and catabolism. Usually only produced in hepatocytes, in fasting conditions other tissues such as the intestines, muscles, brain and kidneys are able to produce glucose following activation of gluconeogenesis.
Glucose transport in yeastIn Saccharomyces cerevisiae glucose transport takes place through facilitated diffusion. The transport proteins are mainly from the Hxt family, but many other transporters have been identified.
Glucose transport in MammalsGLUTs are integral membrane proteins that contain 12 membrane-spanning helices with both the amino and carboxyl termini exposed on the cytoplasmic side of the plasma membrane. GLUT proteins transport glucose and related hexoses according to a model of alternate conformation,  which predicts that the transporter exposes a single substrate binding site toward either the outside or the inside of the cell. Binding of glucose to one site provokes a conformational change associated with transport, and releases glucose to the other side of the membrane. The inner and outer glucose-binding sites are, it seems, located in transmembrane segments 9, 10, 11; also, the QLS motif located in the seventh transmembrane segment could be involved in the selection and affinity of transported substrate.
TypesEach glucose transporter isoform plays a specific role in glucose metabolism determined by its pattern of tissue expression, substrate specificity, transport kinetics, and regulated expression in different physiological conditions. To date, 13 members of the GLUT/SLC2 have been identified. On the basis of sequence similarities, the GLUT family has been divided into three subclasses. Class I Class I comprises the well-characterized glucose transporters GLUT1-GLUT4. N a Distribution Notes m e Levels in cell membranes are increased by G Is widely distributed in fetal tissues. In the reduced glucose levels and decreased by L adult, it is expressed at highest levels in increased glucose levels. U erythrocytes and also in the endothelial cells of barrier tissues such as the blood
brain barrier. However, it is responsiblefor the low-level of basal glucose uptake required to sustain respiration in all cells. Is a bidirectional transporter, allowing glucose to flow in 2 directions. Is expressed by renal tubular cells, small intestinal epithelial cells, liver cells and pancreatic beta cells. Bidirectionality is required in liver cells to uptake glucose for glycolysis, and release of glucose during gluconeogenesis. In pancreatic beta cells, free flowing glucose is required so that the intracellular environment of these cells can accurately gauge the serum glucose levels. All three monosaccharides (glucose, galactose and fructose) are transported from the intestinal mucosal cell into the portal circulation by GLUT2 Expressed mostly in neurons (where it is believed to be the main glucose transporter isoform), and in the placenta.
G L U T 2
Is a high-capacity and low-affinity isoform. There is some evidence that GLUT 1 and 3 are actually the functional transporters in beta cells.
G L U T 3 G L U T 4
Is a high-affinity isoform, allowing it to transport even in times of low glucose concentrations.
Found in adipose tissues and striated muscle (skeletal muscle and cardiac muscle).
Is the insulin-regulated glucose transporter. Responsible for insulin-regulated glucose storage.
Classes II/III Class II comprises: GLUT5 (SLC2A5), a fructose transporter GLUT7 - SLC2A7 - (SLC2A7), transporting glucose out of the endoplasmic
Class III comprises: GLUT6 (SLC2A6), GLUT8 (SLC2A8), GLUT10 (SLC2A10), GLUT12 (SLC2A12), and the H+/myoinositol transporter HMIT (SLC2A13). Most members of classes II and III have been identified recently in homology searches of EST databases and the sequence information provided by the various genome projects. The function of these new glucose transporter isoforms is still not clearly defined at present. Several of
reticulum  GLUT9 - SLC2A9 - (SLC2A9) GLUT11 (SLC2A11)
them (GLUT6, GLUT8) are made of motifs that help retain them intracellularly and therefore prevent glucose transport. Whether mechanisms exist to promote cell-surface translocation of these transporters is not yet known, but it has clearly been established that insulin does not promote GLUT6 and GLUT8 cell-surface translocation.
Discovery of sodium-glucose cotransportIn August 1960, in Prague, Robert K. Crane presented for the first time his discovery of the sodium-glucose cotransport as the mechanism for intestinal glucose absorption. Crane's discovery of cotransport was the first ever proposal of flux coupling in biology. 
NeurotransmitterFrom Wikipedia, the free encyclopedia Jump to: navigation, search For an introduction to concepts and terminology used in this article, see Chemical synapse. Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane in the axon terminal, on the presynaptic side of a synapse. They are released into and diffuse across the synaptic cleft, where they bind to specific receptors in the membrane on the postsynaptic side of the synapse. Release of neurotransmitters usually follows arrival of an action potential at the synapse, but may also follow graded electrical potentials. Low level "baseline" release also occurs without electrical stimulation. Neurotransmitters are synthesized from plentiful and simple precursors, such as amino acids, which are readily available from the diet and which require only a small number of biosynthetic steps to convert.
Types of neurotransmittersThere are many different ways to classify neurotransmitters. Dividing them into amino acids, peptides, and monoamines is sufficient for some classification purposes. Major neurotransmitters: Amino acids: glutamate, aspartate, D-serine, -aminobutyric acid (GABA),
glycine Monoaminesand other biogenic amines: dopamine (DA), norepinephrine (noradrenaline; NE, NA), epinephrine (adrenaline), histamine, serotonin (SE, 5-HT) Peptides: somatostatin, substance P, opioid peptides Others: acetylcholine (ACh), adenosine, anandamide, nitric oxide, etc. In addition, over 50 neuroactive peptides have been found, and new ones are discovered regularly.Many of these are "co-released" along with a small-molecule transmitter, but in some cases a peptide is the primary transmitter at a synapse. -endorphin is a relatively well known example of a peptide neurotransmitter; it engages in highly specific interactions with opioid receptors in the central nervous system. Single ions, such as synaptically released zinc, are also considered neurotransmitters by some, as are some gaseous molecules such as nitric oxide (NO), hydrogen sulfide (H2S), and carbon monoxide (CO). These are not classical neurotransmitters by the strictest definition, however, because although they have all been shown experimentally to be released by presynaptic terminals in an activity-dependent way, they are not packaged into vesicles. By far the most prevalent transmitter is glutamate, which is excitatory at well over 90% of the synapses in the human brain. The next most prevalent is GABA, which is inhibitory at more than
90% of the synapses that do not use glutamate. Even though other transmitters are used in far fewer synapses, they may be very important functionallythe great majority of psychoactive drugs exert their effects by altering the actions of some neurotransmitter systems, often acting through transmitters other than glutamate or GABA. Addictive drugs such as cocaine and amphetamine exert their effects primarily on the dopamine system. The addictive opiate drugs exert their effects primarily as functional analogs of opioid peptides, which, in turn, regulate dopamine levels.
Excitatory and inhibitorySome neurotransmitters are commonly described as "excitatory" or "inhibitory". The only direct effect of a neurotransmitter is to activate one or more types of receptors. The effect on the postsynaptic cell depends, therefore, entirely on the properties of those receptors. It happens that for some neurotransmitters (for example, glutamate), the most important receptors all have excitatory effects: that is, they increase the probability that the target cell will fire an action potential. For other neurotransmitters, such as GABA, the most important receptors all have inhibitory effects (although there is evidence that GABA is excitatory during early brain development). There are, however, other neurotransmitters, such as acetylcholine, for which both excitatory and inhibitory receptors exist; and there are some types of receptors that activate complex metabolic pathways in the postsynaptic cell to produce effects that cannot appropriately be called either excitatory or inhibitory. Thus, it is an oversimplification to call a neurotransmitter excitatory or inhibitorynevertheless it is so convenient to call glutamate excitatory and GABA inhibitory that this usage is seen very frequently.
ActionsMain article: Neuromodulation As explained above, the only direct action of a neurotransmitter is to activate a receptor. Therefore, the effects of a neurotransmitter system depend on the connections of the neurons that use the transmitter, and the chemical properties of the receptors that the transmitter binds to. Here are a few examples of important neurotransmitter actions: Glutamateis used at the great majority of fast excitatory synapses in the brain and spinal cord. It is also used at most synapses that are "modifiable", i.e. capable of increasing or decreasing in strength. Modifiable synapses are thought to be the main memory-storage elements in the brain. Excessive glutamate release can lead to excitotoxicity causing cell death. GABAis used at the great majority of fast inhibitory synapses in virtually every part of the brain. Many sedative/tranquilizing drugs act by enhancing the effects of GABA. Correspondingly glycine is the inhibitory transmitter in the spinal cord. Acetylcholineis distinguished as the transmitter at the neuromuscular junction connecting motor nerves to muscles. The paralytic arrow-poison curare acts by blocking transmission at these synapses. Acetylcholine also operates in many regions of the brain, but using different types of receptors. Dopaminehas a number of important functions in the brain. It plays a critical role in the reward system, but dysfunction of the dopamine system is also implicated in Parkinson's disease and schizophrenia. Serotoninis a monoamine neurotransmitter. Most is produced by and found in the intestine (approximately 90%), and the remainder in central nervous system neurons. It functions to regulate appetite, sleep, memory and learning, temperature, mood, behaviour, muscle contraction, and function of the cardiovascular system and endocrine system. It is speculated to have a role in depression, as some depressed patients are seen to have lower concentrations of metabolites of serotonin in their cerebrospinal fluid and brain tissue. Substance Pis an undecapeptide responsible for transmission of pain from certain sensory
neurons to the central nervous system. Neurons expressing certain types of neurotransmitters sometimes form distinct systems, where activation of the system affects large volumes of the brain, called volume transmission. Major neurotransmitter systems include the noradrenaline (norepinephrine) system, the dopamine system, the serotonin system and the cholinergic system. Drugs targeting the neurotransmitter of such systems affect the whole system; this fact explains the complexity of action of some drugs. Cocaine, for example, blocks the reuptake of dopamine back into the presynaptic neuron, leaving the neurotransmitter molecules in the synaptic gap longer. Since the dopamine remains in the synapse longer, the neurotransmitter continues to bind to the receptors on the postsynaptic neuron, eliciting a pleasurable emotional response. Physical addiction to cocaine may result from prolonged exposure to excess dopamine in the synapses, which leads to the downregulation of some postsynaptic receptors. After the effects of the drug wear off, one might feel depressed because of the decreased probability of the neurotransmitter binding to a receptor. Prozac is a selective serotonin reuptake inhibitor (SSRI), which blocks re-uptake of serotonin by the presynaptic cell. This increases the amount of serotonin present at the synapse and allows it to remain there longer, hence potentiating the effect of naturally released serotonin. AMPT prevents the conversion of tyrosine to L-DOPA, the precursor to dopamine; reserpine prevents dopamine storage within vesicles; and deprenyl inhibits monoamine oxidase (MAO)-B and thus increases dopamine levels. Diseases may affect specific neurotransmitter systems. For example, Parkinson's disease is at least in part related to failure of dopaminergic cells in deep-brain nuclei, for example the substantia nigra. Treatments potentiating the effect of dopamine precursors have been proposed and effected, with moderate success. A brief comparison of the major neurotransmitter systems follows:
Precursors of neurotransmittersWhile intake of neurotransmitter precursors does increase neurotransmitter synthesis, evidence is mixed as to whether neurotransmitter release (firing) is increased. Even with increased neurotransmitter release, it is unclear whether this will result in a long-term increase in neurotransmitter signal strength, since the nervous system can adapt to changes such as increased neurotransmitter synthesis and may therefore maintain constant firing. Some neurotransmitters may have a role in depression, and there is some evidence to suggest that intake of precursors of these neurotransmitters may be useful in the treatment of mild and moderate depression.
Dopamine precursors L-DOPA, a precursor of dopamine that crosses the bloodbrain barrier, is used in the treatment of Parkinson's disease. Norepinephrine precursorsFor depressed patients where low activity of the neurotransmitter norepinephrine is implicated, there is only little evidence for benefit of neurotransmitter precursor administration. Lphenylalanine and L-tyrosine are both precursors for dopamine, norepinephrine, and epinephrine. These conversions require vitamin B6, vitamin C, and Sadenosylmethionine. A few studies suggest potential antidepressant effects of L-phenylalanine and L-tyrosine, but there is much room for further research in this area.
Administration of L-tryptophan, a precursor for serotonin, is seen to double the production of serotonin in the brain. It is significantly more effective than a placebo in the treatment of mild and moderate depression. This conversion requires vitamin C. 5-hydroxytryptophan (5HTP), also a precursor for serotonin, is also more effective than a placebo.
Degradation and eliminationA neurotransmitter must be broken down once it reaches the post-synaptic cell to prevent further excitatory or inhibitory signal transduction. For example, acetylcholine (ACh), an excitatory neurotransmitter, is broken down by acetylcholinesterase (AChE). Choline is taken up and recycled by the pre-synaptic neuron to synthesize more ACh. Other neurotransmitters such as dopamine are able to diffuse away from their targeted synaptic junctions and are eliminated from the body via the kidneys, or destroyed in the liver. Each neurotransmitter has very specific degradation pathways at regulatory points, which may be the target of the body's own regulatory system or recreational drugs.
DystrophinFrom Wikipedia, the free encyclopedia Jump to: navigation, search Dystrophin is a rod-shaped cytoplasmic protein, and a vital part of a protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane. This complex is variously known as the costamere or the dystrophinassociated protein complex. Many muscle proteins, such as -dystrobrevin, syncoilin, synemin, sarcoglycan, dystroglycan, and sarcospan, colocalize with dystrophin at the costamere. The Dystrophin gene is one of the longest human genes known, covering 2.2 megabases (0.07% of the human genome) at locus Xp21. The primary transcript measures about 2,400 kilobases and takes 16 hours to transcribe; the mature mRNA measures 14.0 kilobases. The 79 exons code for a protein of over 3500 amino acid residues.
PathologyDystrophin deficiency has been definitively established as one of the root causes of the general class of myopathies collectively referred to as muscular dystrophy. The large cytosolic protein was first identified in 1987 by Louis M. Kunkel, after the 1986 discovery of the mutated gene that causes Duchenne muscular dystrophy (DMD) . Normal skeletal muscle tissue contains only small amounts of dystrophin (about 0.002% of total muscle protein), but its absence (or abnormal expression) leads to the development of a severe and currently incurable constellation of symptoms most readily characterized by several aberrant intracellular signaling pathways that ultimately yield pronounced myofiber necrosis as well as progressive muscle weakness and fatigability. Most DMD patients become wheelchair-dependent early in life, and the gradual development of cardiac hypertrophya result of severe myocardial fibrosis typically results in premature death in the first two or three decades of life. Mutations in the dystrophin gene that lead to the production of less defective, but still only partially functional dystrophin protein, result in a display of a much milder dystrophic phenotype in affected patients, resulting in the disease known as Becker's muscular dystrophy (BMD). In some cases the patient's phenotype is such that experts may decide differently on whether a patient should be diagnosed with DMD or BMD. The theory currently most commonly used to predict whether a mutation will result in a DMD or BMD phenotype, is the reading frame rule.
Though its role in airway smooth muscle is not well established, recent research indicates that dystrophin along with other subunits of dystrophin glycoprotein complex is associated with phenotype maturation.
InteractionsDystrophin has been shown to interact with SNTB1, Syntrophin, alpha 1 and DTNA.
Factor VIIIFrom Wikipedia, the free encyclopedia Jump to: navigation, search Coagulation factor VIII, procoagulant component
PDB rendering based on 1d7p. Available structures P Ortholog search: PDBe, RCSB D [show]List of PDB id codes
Symbol sExternal IDs
F8; AHF; DXS1253E; F8B; F8C; FVIII; HEMAOMIM: 300841MGI: 88383HomoloGene: 49153ChEMBL: 3143 GeneCards: F8 Gene [show]Gene Ontology RNA expression pattern
More reference expression dataOrthologs Species Human Mouse
Entrez Ensemb l UniProtRefSeq (mRNA) RefSeq (protein) Location (UCSC)
2157 ENSG00 0001850 10 P00451 NM_000 132.3 NP_0001 23.1 Chr X: 154.06 154.26 Mb 
14069 ENSMUSG 000000311 96 Q06194 NM_00116 1373.1 NP_001154 845.1 Chr X: 75.17 75.38 Mb This box: view talk
Factor VIII (FVIII) is an essential blood-clotting protein, also known as anti-hemophilic factor (AHF). In humans, factor VIII is encoded by the F8 gene. Defects in this gene results in hemophilia A, a recessive X-linked coagulation disorder. Factor VIII participates in blood coagulation; it is a cofactor for factor IXa which, in the presence of Ca+2 and phospholipids forms a complex that converts factor X to the activated form Xa. The factor VIII gene produces two alternatively spliced transcripts. Transcript variant 1 encodes a large glycoprotein, isoform a, which circulates in plasma and associates with von Willebrand factor in a noncovalent complex. This protein undergoes multiple cleavage events. Transcript variant 2 encodes a putative small protein, isoform b, which consists primarily of the phospholipid binding domain of factor VIIIc. This binding domain is essential for coagulant activity. People with high levels of factor VIII are at increased risk for deep vein thrombosis and pulmonary embolism.
Contents1 Genetics 2 Physiology 3 Therapeutic use 4 Contamination scandal 5 See also 6 References 7 Further reading 8 External links
GeneticsThe gene for factor VIII is located on the X chromosome (Xq28). The gene for factor VIII presents an interesting primary structure, as another gene is embedded in one of its introns.
PhysiologyFVIII is a glycoprotein procofactor. Although the primary site of release in humans is ambiguous, it is synthesized and released into the bloodstream by the vascular, glomerular, and tubular endothelium, and the sinusoidal cells of the liver. Hemophilia A has been corrected by liver transplantation. Transplanting hepatocytes was ineffective, but liver endothelial cells were effective. In the blood, it mainly circulates in a stable noncovalent complex with von Willebrand factor. Upon activation by thrombin, (factor IIa), it dissociates from the complex to interact with factor IXa in the coagulation cascade. It is a cofactor to factor IXa in the activation of factor X, which, in turn, with its cofactor factor Va, activates more thrombin. Thrombin cleaves fibrinogen into fibrin which polymerizes and crosslinks (using factor XIII) into a blood clot. No longer protected by vWF, activated FVIII is proteolytically inactivated in the process (most prominently by activated protein C and factor IXa) and quickly cleared from the blood stream. Factor VIII is not affected by liver disease. In fact, levels usually are elevated in such instances.
Therapeutic useFVIII concentrated from donated blood plasma (Aafact or Alphanate), or alternatively recombinant FVIII can be given to hemophiliacs to restore hemostasis. The transfer of a plasma byproduct into the blood stream of a patient with hemophilia often led to the transmission of diseases such as hepatitis B and C and HIV before purification methods were improved. Antibody formation to factor VIII can also be a major concern for patients receiving therapy against bleeding; the incidence of these inhibitors is dependent of various factors, including the factor VIII product itself.
ProteolysisFrom Wikipedia, the free encyclopedia
(Redirected from Protein degradation) Jump to: navigation, search Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. This generally occurs by the hydrolysis of the peptide bond, and is most commonly achieved by cellular enzymes called proteases, but may also occur by intramolecular digestion, as well as by nonenzymatic methods such as the action of mineral acids and heat. Proteolysis in organisms serves many purposes; for example, digestive enzymes break down proteins in food to provide amino acids for the organism, while proteolytic processing of polypeptide chain after its synthesis may be necessary for the production of an active protein. It is also important in the regulation of some physiological and cellular processes, as well as preventing the accumulation of unwanted or abnormal proteins in cells.
Contents1 Post-translational proteolytic processing o 1.1 Removal of N-terminal methionine o 1.2 Removal of the signal sequence o 1.3 Cleavage of polyprotein o 1.4 Cleavage of precursor proteins 2 Protein degradation o 2.1 Lysosome and proteasome o 2.2 Rate of intracellular protein degradation o 2.3 Digestion 3 Proteolysis in cellular regulation o 3.1 Cell cycle regulation o 3.2 Apoptosis 4 Regulatiory domains in proteolysis 5 Proteolysis and diseases 6 Laboratory applications 7 Venoms 8 See also 9 References 10 External links
Post-translational proteolytic processingLimited proteolysis of a polypeptide during or after translation in protein synthesis often occur for many proteins. This may involved removal of the N-terminal methionine, signal peptide, and/or the conversion of an inactive or non-functional protein to an active one. The precursor to the final functional form of protein is termed proprotein, and these proproteins may be first synthesized as preproprotein. For example, albumin is first synthesized as preproalbumin and contains an uncleaved signal peptide. This forms the proalbumin after the signal peptide is cleaved, and a further
processing to remove the N-terminal 6-residue propeptide yields the mature form of the protein.
Removal of N-terminal methionineThe initiating methonine (and in prokaryotes, fMet) may be removed during translation of the nascent protein. For E. coli, fMet is efficiently removed if the second residue is small and uncharged, but not if the second residue is bulky and charged. In both prokaryotes and eukaryotes, the exposed N-terminal residue may determine the half-life of the protein according to the N-end rule.
Removal of the signal sequenceProteins that are to be targeted to a particular organelle or for secretion have an N-terminal signal peptide that directs the protein to its final destination. This signal peptide is removed by proteolysis after their transport through a membrane.
Cleavage of polyproteinSome proteins and most eukaryotic polypeptide hormones are synthesized as a large precursor polypeptide known as polyprotein that require proteolytic cleavage into individual smaller polypeptide chains. The polyprotein pro-opiomelanocortin (POMC) contains many polypeptide hormones. The cleavage pattern of POMC however may vary between different tissues, yielding different sets of polypeptide hormones from the same polyprotein. Many viruses also produce their proteins initially as a single polypeptide chain that were translated from a polycistronic mRNA. This polypeptide is subsequently cleaved into individual polypeptide chains.
Cleavage of precursor proteinsMany proteins and hormones are synthesized as in the form of their precursors - (zymogens, proenzymes and prehormones). These proteins are cleaved to form their final active structures. Insulin, for example, is synthesized as preproinsulin and forms proinsulin after the signal peptide has been cleaved. To form the mature insulin, the proinsulin is then cleaved at two positions to yield two polypeptide chains linked by 2 disulphide bonds. Proinsulin is necessary for the folding of the polypeptide chain as the 2 polypeptide chains of insulin may not correctly assemble into the correct form while its precursor proinsulin do. Proteases in particular are synthesized in the inactive form so that they may be safely stored in cells and ready for released in sufficient quantity when required, and to ensure that the protease is only activated in the correct location or context. Inappropriate activation of these proteases can be very destructive for an organism. Proteolysis of the zymogen yield an active protein; for example, when trypsinogen is cleaved to form trypsin, a slight rearrangement of the protein structure occurs which completes the active site of the protease, thereby activating the protein. Proteolysis can therefore be a method of regulating biological processes. A good example is the blood clotting cascade whereby an initial event triggers a cascade of sequential proteolytic activation of many specific proteases, resulting in blood coagulation. The complement system of the immune response also involves a complex sequential proteolytic activation and interaction that result in an attack on invading pathogens.
Proteolytic cleavage breaks down proteins in food extracellularly into smaller peptides and amino acids so that they may be absorbed and used by an organism. Proteins in cells are also constantly being broken down into amino acids. This intracellular degradation of protein serves a number of functions it removes damaged and abnormal protein and prevent their accumulation, and it also serves to regulate cellular processes by removing enzymes and regulatory proteins that are no longer needed. The amino acids may then be reused for protein synthesis.
Structure of a proteasome. Its active sites are inside the tube (blue) where proteins are degraded.
Lysosome and proteasomeThe intracellular degradation of protein may be achieved in two ways - proteolysis in lysosome, or a ubiquitin-dependent process which targets unwanted proteins to proteasome. The autophagy-lysosomal pathway is normally a non-selective process but may become selective upon starvation whereby protein with peptide sequence KFERQ or similar are selectively broken down. The lysosome contains a large number of proteases such as cathepsins. The ubiquitin-mediated process is selective. Proteins marked for degradation are covalently linked to ubiquitin. Many molecules of ubiquitin may be linked in tandem to a protein destined for degradation. The polyubiquinated protein is targeted to an ATP-dependent protease complex, the proteasome. The ubiquitin is released and reused, and the targeted protein is degraded.
Rate of intracellular protein degradationDifferent proteins are degraded at different rate. Abnormal proteins are quickly degraded, while the rate of degradation of normal proteins may vary widely depending on their functions. Enzymes at important metabolic control points may be degraded much faster than those enzymes whose activity is largely constant under all physiological conditions. One of the most rapidly degraded protein is ornithine decarboxylase which has a half-life of 11 minutes. In contrast, other proteins like actin and myosin have half-life of a month or more, while haemoglobin essentially lasts for the entire life-time of erythrocyte. The N-end rule may partially determine the half-life of a protein, and proteins with segments rich in proline, glutamine, serine, and threonine (the so-called PEST proteins) have short halflife. Other factors suspected to affect degradation rate include the rate deamination of glutamine and asparagine and oxidation of cystein, histidine and methionine, the absence of stabilizing ligands, the presence of attached carbohydrate or phosphate groups, the presence of free -amino group, the negative charge of protein, and the flexibility and stability of the protein. The rate of proteolysis may also depend on the physiological state of the cell, such as its hormonal state as well as nutritional status. In time of starvation, the rate of protein degradation increases.
DigestionIn human digestion, proteins in food are broken down into smaller peptide chains by digestive enzymes such as pepsin, trypsin, chymotrypsin, and elastase, and into amino acids by various enzymes such as carboxypeptidase, aminopeptidase and dipeptidase. It is necessary to break down proteins into small peptides (tripeptides and dipeptides) and amino acids so they can be absorbed by the intestines, and the absorbed tripeptides and dipeptides are also further broken into amino acids intracellularly before they enter the bloodstream. Different enzymes have different specificity for their substrate; trypsin for example cleaves the peptide bond after a positively charge residue (arginine and lysine), chymotrypsin cleaves the bond after an aromatic residue (phenylalanine, tyrosine, and tryptophan), elastase cleaves the bond after a small non-polar residue such as alanine or glycine. In order to prevent inappropriate or premature activation of the digestive enzymes (they may, for example, trigger pancreatic self-digestion), these enzymes are secreted as inactive zymogen. The precursor of pepsin, pepsinogen, is secreted by the stomach, and is activated only in only in the acidic environment found in stomach. The pancreas secretes the precursors of a number of proteases, such trypsin and chymotrypsin. The zymogen of trypsin is trypsinogen which is activated by a very specific protease, enterokinase, which is secreted by the mucosa of the duodenum. The trypsin, once activated, can also cleave other trypsinogen as well as the precursors of other proteases such as chymotrypsin and carboxypeptidase. In bacteria, a similar strategy of employing an inactive zymogen or prezymogen is used. Subtilisin which is produced by Bacillus subtilis is produced as preprosubtilisin, and is released only if the signal peptide is cleaved and autocatalytic proteolytic activation has occurred.
Proteolysis in cellular regulationProteolysis is also involved in the regulation of many cellular processes by activating or deactivating enzymes, transcription factors, and receptors, for example in the biosynthesis of cholesterol, or the mediation of thrombin signalling through protease-activated receptors. Some enzymes at important metabolic control points such as ornithine decarboxylase is regulated entirely by its rate of synthesis and its rate of degradation. Other rapidly degraded proteins include the protein products of proto-oncogenes which play central roles in the regulation of cell growth.
Cell cycle regulation Cyclins are a group of proteins that activate kinases involved in cell division. The degradation of cyclins is the key step that governs the exit from mitosis and progress into the next cell cycle. Cyclins accumulate in the course the cell cycle, then abruptly disappear just before the anaphase ofmitosis. The cyclins are removed via a ubiquitin-mediated proteolytic pathway.
Apoptosis Caspases are a important group of proteases involved in apoptosis.
Regulatiory domains in proteolysisProtease may have one or more regulatory domains Calcium-binding domain - e.g. prothrombin, factor IX, X, VII, protein C in blood clotting cascade, calpain. Kringle domain- e.g. in prothrombin it keeps the protease inactive.
Proteolysis and diseasesAbnormal proteolytic activity are associated with many diseases. In pancreatitis, leakage of proteases and their premature activation in the pancreas results in the self-digestion of the pancreas. People with diabetes mellitus may have increased lysosomal activity and the degradation of some proteins can increase significantly. Chronic inflammatory diseases such as rheumatoid arthritis may involve the release of lysosomal enzymes into extracellular space which break down surrounding tissues. Abnormal proteolysis and generation of peptides that aggregate in cells and their ineffective removal may result in many age-related neurological diseases such as Alzheimer. Other diseases linked to aberrant proteolysis include muscular dystrophy, degenerative skin disorders, respiratory and gastrointestinal diseases, and malignan
CFTR inhibitory factorFrom Wikipedia, the free encyclopedia Jump to: navigation, search
Ribbon diagramof the Cif dimer from P. aeruginosa PA14. From PDB 3KD2. The CFTR inhibitory factor (Cif) is a protein virulence factor secreted by the Gram-negative bacterium Pseudomonas aeruginosa. Discovered at Dartmouth Medical School, Cif is able to alter the trafficking of select ABC transporters in eukaryotic epithelial cells, such as the cystic fibrosis transmembrane conductance regulator (CFTR), and P-glycoprotein by interfering with the host deubiquitinating machinery. By promoting the ubiquitin-mediated
degradation of CFTR, Cif is able to phenocopy cystic fibrosis at the cellular level. The cif gene is transcribed as part of a 3 gene operon, whose expression is negatively regulated by CifR, a TetR family repressor.
Cellular mechanism of actionCif was first discovered by co-culturing P. aeruginosa with human airway epithelial cells and monitoring the resulting effect on chloride ion efflux across a polarized monolayer. After co-culture, the CFTR specific chloride ion efflux was found to be drastically reduced. This was determined to be caused by reduced levels of CFTR at the apical surface of these cells. This effect was later found to be the result of a single secreted protein produced by P. aeruginosa, which was named the CFTR inhibitory factor for this initial phenotype. Cif is secreted by P. aeruginosa PA14 as soluble protein as well as packaged into outer membrane vesicles (OMV). Cif is far more potent when applied in OMVs, likely due to efficiency of delivery. Purified, recombinant Cif protein can be applied to polarized monolayers of mammalian cells and promote the removal of CFTR and Pglycoprotein from the apical membrane. Cif accomplishes this by interfering with the host deubiquitylation system.
Epoxide hydrolase enzyme mechanism The active site of Cif is shown with a C trace in gray, and side chains of select residues playing a role in catalysis are displayed as sticks. From PDB 3KD2. Cif is an epoxide hydrolase (EH) with unique substrate selectivity. Cif is the first example of an EH serving as a virulence factor. Based on structural comparison, it appears that the enzyme utilizes a catalytic triad of residues Asp129, Glu153 and His297, with accessory residues His177 and Tyr239 coordinating the epoxide oxygen during ring opening. Cif is also the first example of an EH utilizing a His-Tyr pair to coordinate an epoxide substrate, rather than the canonical Tyr-Tyr pair. In the proposed enzyme mechanism, Asp129 nucleophilically attacks a carbon of the epoxide moiety of a substrate, forming an ester linked enzyme-acyl intermediate. The preference for which carbon is attacked varies depending upon the substrate. In the second step of the reaction, a water molecule is activated by the charge-relay His297-Glu153 pair, and undergoes nucleophilic attack on the C of Asp129. This hydrolyzes the ester group, liberating the hydrolysis product as a vicinal diol.
StructureCif belongs to the / hydrolase family of proteins. Its structure was determined by X-ray crystallography and consists of the canonical / hydrolase fold with a cap domain, which it uses to constitutively homo-dimerize in solution. The active site is burred in the interior of the protein at the interface between the / hydrolase core and the cap.
Apolipoprotein BFrom Wikipedia, the free encyclopedia Jump to: navigation, search Apolipoprotein B (including Ag(x) antigen) Identifiers
Symbol sExternal IDs
APOB; FLDB; LDLCQ4OMIM: 107730MGI: 88052HomoloGene: 328ChEMBL: 4549 GeneCards: APOB Gene [show]Gene Ontology RNA expression pattern
More reference expression dataOrthologs Species Human Mouse
Entrez Ensemb l UniProtRefSeq (mRNA) RefSeq (protein) Location (UCSC)
338 ENSG00 0000846 74 P04114 NM_000 384.2 NP_000 375.2 Chr 2: 21.22 21.27 Mb 
238055 ENSMUSG 000000206 09 E9Q1Y3 NM_00969 3.2 NP_033823 .2 Chr 12: 7.98 8.02 Mb This box: view talk
Apolipoprotein B (APOB or ApoB) are the primary apolipoproteins of chylomicrons and lowdensity lipoproteins (LDL - known commonly by the misnomer "bad cholesterol" when in reference to heart disease), which is responsible for carrying cholesterol to tissues. While it is unclear exactly what functional role APOB plays in LDL, it is the primary apolipoprotein component and is absolutely required for its formation. What is clear is that the APOB on the LDL particle acts as a ligand for LDL receptors in various cells throughout the body (i.e. less formally, APOB "unlocks" the doors to cells and thereby delivers cholesterol to them). Through a mechanism that is not fully understood, high levels of APOB can lead to plaques that cause vascular disease (atherosclerosis), leading to heart disease. There is considerable evidence that levels of APOB are a better indicator of heart disease risk than total cholesterol or LDL. However, primarily for historic reasons, cholesterol, and more specifically, LDL-cholesterol, remains the primary lipid test for the risk factor of atherosclerosis.
Contents1 Genetic disorders 2 Mouse studies 3 Molecular biology 4 Role in Innate Immune System 5 Role in lipoproteins and atherosclerosis 6 Interactions 7 Interactive pathway map 8 Regulation 9 RNA editing o 9.1 Type o 9.2 Location o 9.3 Regulation o 9.4 Conservation 9.5 Consequences 9.5.1 Structure 9.5.2 Function 10 See also 11 References 12 Further reading 13 External links
Genetic disordersHigh levels of APOB are related to heart disease. Hypobetalipoproteinemia is a genetic disorder that can be caused by a mutation in the APOB gene, APOB. Abetalipoproteinaemia is usually caused by a mutation in the MTP gene, MTP. Mutations in gene ApoB100 can also cause Familial hypercholesterolemia, a hereditary (autosomal dominant) form of metabolic disorder Hypercholesterolemia.
Most relevant information regarding mouse APOB homologue, mApoB, has come from mouse studies. Mice overexpressing mApoB have increased levels of LDL "bad cholesterol" and decreased levels of HDL "good cholesterol". Mice containing only one functional copy of the mApoB gene show the opposite effect, being resistant to hypercholesterolemia. Mice containing no functional copies of the gene are not viable.
Molecular biologyThe protein occurs in the plasma in 2 main isoforms, APOB48 and APOB100. The first is synthesized exclusively by the small intestine, the second by the liver. Both isoforms are coded by APOB and by a single mRNA transcript larger than 16 kb. APOB48 is generated when a stop codon (UAA) at residue 2153 is created by RNA editing. There appears to be a trans-acting tissue-specific splicing gene that determines which isoform is ultimately produced. Alternatively, there is some evidence that a cis-acting element several thousand bp upstream determines which isoform is produced. As a result of the RNA editing, APOB48 and APOB100 share a common N-terminal sequence, but APOB48 lacks APOB100's C-terminal LDL receptor binding region. In fact, APOB48 is so called because it constitutes 48% of the sequence for APOB100. APOB 48 is a unique protein to chylomicrons from the small intestine. After most of the lipids in the chylomicron have been digested, APOB48 returns to the liver as part of the chylomicron remnant, where it is endocytosed and degraded.
Role in Innate Immune SystemVLDL and LDL interfere with the quorum sensing system that upregulates genes required for invasive Staphylococcus aureus infection. The mechanism of antagonism entails binding Apolipoprotein B, to a S. aureus autoinducer pheromone, preventing signaling through its receptor. Mice deficient in apolipoprotein B are more susceptible to invasive bacterial infection.
Role in lipoproteins and atherosclerosisAPOB100 is found in lipoproteins originating from the liver (VLDL, IDL, LDL). Importantly, there is one APOB100 molecule per hepatic-derived lipoprotein. Hence, using that fact, one can quantify the number of lipoprotein particles by noting the total APOB100 concentration in the circulation. Since there is one and only one APOB100 per particle, the number of particles is reflected by the APOB100 concentration. The same technique can be applied to individual lipoprotein classes (e.g. LDL) and thereby enable one to count them as well. It is well established that APOB100 levels are associated with coronary heart disease, and are even a better predictor of it than is LDL level. A naive way of explaining this observation is to use the idea that APOB100 reflects lipoprotein particle number (independent of their cholesterol content). In this way, one can infer that the number of APOB100-containing lipoprotein particles is a determinant of atherosclerosis and heart disease. One way to explain the above is to consider that large numbers of lipoprotein particles, and, in particular large numbers of LDL particles, lead to competition at the APOB100 receptor (i.e. LDL receptor) of peripheral cells. Since such a competition will prolong the residence time of LDL particles in the circulation, it may lead to greater opportunity for them to undergo oxidation and/or other chemical modifications. Such modifications may lessen the particles' ability to be cleared by the classic LDL receptor and/or increase their ability to interact with so-called "scavenger" receptors. The net result is shunting of LDL particles to these scavenger receptors. Scavenger receptors typically are found on macrophages, with cholesterol laden macrophages being better known as "foam cells". Foam cells characterize atherosclerotic lesions. In addition to this possible mechanism of foam cell
generation, an increase in the levels of chemically modified LDL particles may also lead to an increase in endothelial damage. This occurs as a result of modified-LDL's toxic effect on vascular endothelium as well its ability both to recruit immune effector cells and to promote platelet activation. Recently, the INTERHEART study found that the ApoB100 / ApoA1 ratio is more effective at predicting heart attack risk, in patients who had had an acute myocardial infarction, than either the ApoB100 or ApoA1 measure alone. In the general population this remains unclear although in a recent study apoB was the strongest risk marker for cardiovascular events. A small study suggests that added to fluvastatatin treatment, omega 3 fatty acids daily, containing 460 mg of E-EPA and 380 mg of E-DHA (ethyl esters), may lower apo B48 in hyperlipemic type 2 diabetics.[6