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Published byMitchell Felix Miller Modified over 9 years ago
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Signal transduction in bacterial chemotaxis Lengeler et al. pp. 514-523
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Chemotaxis: responses E. coli –Makes temporal comparisons –Responds to spatial gradients –Compares environment of present with environment of past –Time: 1 to 2 sec
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Expt –expose E. coli to stepwise change of… [ATTractant] or [REPellant] 1. Isotropic conditions: S T –Sudden increase in [ATT] S Excitation response = fast: < 0.2 sec –Same [ATT]: S T Sensory adaptation = slow: sec to min
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2. Isotropic conditions: S T –Sudden increase in [REP] T Excitation response = fast, < 0.2 sec –Same [REP]: S T Sensory adaptation = slow, sec to min Conclusion –Cell seeks “better” environment……
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stages Cell… samples its chemical environment Makes comparison between current conditions and past conditions Response: if better, suppresses tumbling; more smooth swimming ……………if worse, no suppression of tumbling ……………if no change, alternate S, T Updates of short-term memory
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Chemotaxis: components 4 receptor proteins Signal transduction proteins Adaptation proteins 4 receptors = methyl-accepting chemotaxis proteins (MCPs) span CM
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4 receptors Tsr Taxis serine and some repellents; Leu = rep; acids = rep Tar Taxis aspartate and some repellents Maltose = attractant Trg Taxis ribose and galactose Tap Taxis to dipeptides
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Chemotaxis: components Signal transduction proteins CheA CheY CheW CheZ Adaptation proteins CheR CheB
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MCPs NH 3 -----TM1-------- highly variable sensory domain -------- -TM2-------- linker --------MH1-------- seq conservation; signaling domain --------MH2---------COOH TM = transmembrane segment MH = methylated helix Sensory domain: periplasm Signaling domain: cytoplasm
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Signal transduction Excitation –Bind REP to MCP in CM –MCP sends signal via CheW CheW: adaptor / intermediate in cytoplasm CheW: mediates signals to CheA –CheA = protein kinase on binding of REP, increased CheA kinase autoP @ His48 increase CheA~P
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Excitation, cont’d –CheA~P + CheY CheY~P CheY~P @ Asp57 = tumble factor CheY~P binds to FliM of flagellar switch Signal = CW rotation = tumbling
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–Bind ATT to MCP in CM –MCP sends signal via CheW –CheW CheA –CheA = protein kinase on bdg of ATT, decreased CheA kinase Lower autoP lower CheA~P –Lower CheA~P + CheY lower CheY~P Signal = CCW rotation = smooth Excitation = ~P and de~P
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Signal transduction Adaptation CheR + CheB + MCPs [ATT] –converted into intracellular “short term memory” –registered as methylated MCP
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Adaptation MCP + CheR (methyltransferase) MCP-CH 3 Methyl group = S-AdoMet Each MCP: methylated at Glu Methyl’n affects {MCP – CheW – CheA} communication MCP-CH 3 + CheB (methylesterase) MCP + CH 3 OH
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Extent of methylation affects –kinase activity of CheA –Rate of producing CheY~P Complex interplay of CheR and CheB Outcome: –Adaptation restores CheY~P to same levels as before stimulus
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