2. Bacterial Signal Transduction.ppt

8/10/2019 2. Bacterial Signal Transduction.ppt

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Bacterial Signal Transduction

Transduksi Sinyal pada Bakteri


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Bacterial Signal TransductionBagian dari Cell Communication


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Mengapa sel harus berkomunikasi?

Untuk mengkoordinasikan proses kehidupan.Organisme multiselular memiliki miliaran sel yangharus berkomunikasi untuk berkembang danbertahan hidup. Komunikasi antar sel juga penting

untuk organisme uniseluler.

Ahli biologi telah menemukan beberapa mekanismeuniversal regulasi seluler, yang melibatkanmekanisme sinyal sel ( ce l l-s ign a ling m ech anism s ).

Sel dapat menerima berbagai sinyal: sinyal kimia,sinyal elektromagnetik, dan sinyal mekanik.


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Komunikasi antar sel

Example: Saccharomycescerevisiae the fungus thathumans have used forcenturies to make bread, wine,and beer. Use of chemicalsignal to find potentialmates . Alpha () and a cells :


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Signal Transduction Signal transduction at the cellular level refers to the

movement of signals from outside the cell to inside.

Bacterial Signal Transduction: Two-ComponentRegulatory Systems

In order to respond to changes in environmentalparameters, cells must be able to transmit theinformation from the cell surface (site of induction) to thecytoplasm (site of cellular response).

Definition: the action or process of converting something and especially

energy or a message into another form


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Two-Component Sensory TransductionGeneral Mechanism

These systems consist of two separate proteins. Thefirst of these, the sensor/initiator [sensor kinase] , istasked with reading an aspect of the environment andgenerating a signal.

The second, the response regulator , must receivethe signal from the first protein and then act upon it insome way.

Note: Many enzymes are regulated by phosphory la t ion . A phosphategroup is attached to the enzyme by another enzyme, called a prote inkinase . When the enzyme is phosphorylated it changes its shape andthus its activity. Phosphorylation activates some enzymes andinactivates others; by this means one protein kinase can control severalenzymes.


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General Mechanism of Signal TransductionMekanisme Umum Transduksi Sinyal


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Two-Component Systems consistsof two proteins, a sensor histidinekinase and a response regulator.Both proteins harbor two functionalimportant domains: The histidinekinase detects a specificenvironmental stimulus through itssensor domain (input 1) .This leads to a conformationalchange (2) , resulting in ATP-

dependent autophosphorylation of ainvariant His residue (3) . His~Pserves as the phosphate donor forthe receiver domain of the cognateresponse regulator, resulting inphosphorylation of a conserved Aspresidue and subsequently its

dimerization (4) . This ultimatelyleads to an activation of the effectordomain of the response regulator,mediating the cellular response(= output 5) , usually by mediatingdifferential expression of specifictarget genes (= regulon 6).


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Reseptor sinyal: kebanyakanberupa protein membran plasma

Kebanyakan molekul sinyal adalah molekul larutdalam air dan ukurannya terlalu besar untuk melewatimembran plasma.

Molekul sinyal mempengaruhi aktivitas sel dengan

mengikat protein reseptor pada membran plasma. Pengikatan molekul sinyal ini menyebabkan

perubahan bentuk reseptor atau agregasi reseptor. Hal ini memicu perubahan dalam lingkungan

intraselular. Tiga jenis utama reseptor adalah reseptor terikat

protein-G , reseptor tirosin kinase , dan reseptorion-channel .


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Binding ofmessenger --Chemical messengerbinds to receptorprotein, and the proteinchanges shape(conformationalchange.) Themessenger fits into thereceptor like a key in alock it behaves as aligand .

G-protein-linkedreceptors


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Tyrosine-kinasereceptors

The fully-activated receptorproteins activate a variety ofspecific relay proteins thatbind to specificphosphorylated tyrosine

molecules. One tyrosine-kinasereceptor dimer mayactivate ten or moredifferent intracellular

proteins simultaneously. These activated relayproteins trigger manydifferent transductionpathways and

responses.


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Ion-Channelreceptors


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Jalur Transduksi Sinyal Jalur transduksi menyampaikan informasi. Ligan

mengikat ke reseptor pada membran plasma,menyebabkan perubahan konformasi pada reseptor,memicu kejadian beruntun (cascade events) .

Protein reseptor yang diaktifkan mengaktifkanserangkaian protein lain yang menyampaikaninformasi tersebut.

Fosforilasi protein merupakan mekanisme utama daritransduksi sinyal dalam sel.

Protein kinase Protein phosphotase


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Signal Transduction Cascade

When the ligand binds tothe receptor, it triggerssome kind ofconformational changethat induces transduction.In the diagram, aphosphate group is being

passed through aphosphorylation cascade.Finally, there is some typeof response, usually oncethe signal reaches thenucleus, as it triggersgene activation ordeactivation. Someimportant points toremember about signaltransduction pathways arethat they allow cellcommunication, quickresponse, and amplifiedsignals.


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Signal Transductionin Bacterial Chemotaxis


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How do bacteria detect a chemical gradient?

Proteins called CheA and CheW are bound to the receptor. The former is thehistidine kinase for this system. Upon activation of the receptor, the CheA'sconserved histidine residue undergoes autophosphorylation . There are tworesponse regulators called CheB and CheY . There is a transfer of aphosphoryl group to their conserved aspartate residue from CheA. CheYsubsequently interacts with the flagellar switch protein called FliM. This

induces the switching in flagellar direction from counter-clockwise to clockwise.


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Chemotactic SwimmingBehavior

Chemotactic SwimmingMethods


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Physiological Functions :Two-component systems regulate diverse responses including

nutrient acquisition : nitrogen, phosphorus, carbon

energy metabolism : electron transport systems, uptakeand catabolic machinery

adaptation to physical or chemical aspects of the environment: chemotaxis , pH, osmolarity, light quality

complex developmental pathways : sporulation, fruiting bodydevelopment, swarmer cell production

virulence : plasmid transfer ( conjugation ), degredative secretions, toxinproduction

Quorum sensing
http://krebbing.blogspot.com/2007/12/electron-transfer-chain.htmlhttp://krebbing.blogspot.com/2007/12/catabolism.htmlhttp://euarch.blogspot.com/2007/10/bacterial-motility.htmlhttp://euarch.blogspot.com/2007/09/conjugation.htmlhttp://euarch.blogspot.com/2007/09/conjugation.htmlhttp://euarch.blogspot.com/2007/10/bacterial-motility.htmlhttp://krebbing.blogspot.com/2007/12/catabolism.htmlhttp://krebbing.blogspot.com/2007/12/electron-transfer-chain.html


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DctB/DctD - dicarboxylate transport in Rhizobium leguminosarum

EnvZ/OmpR osmoregulation in E. coli

NtrB/NtrC - nitrogen assimilation in a variety of bacteria

PhoR/PhoB - phosphate scavenging in E. coli

VirA/VirG - virulence by Agrobacterium tumefaciens

A 125 amino acid peptide segment is "conserved" in one subset of thesegene products: OmpR, PhoB, NtrC, DctD, VirG

A "homologous" segment is present in these regulatory proteins:

Spo0A - sporulation

Spo0F - sporulation

CheY chemotaxis

CheB chemotaxis

Two-component systems: protein component:

2. Bacterial Signal Transduction.ppt

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