Signal transduction in bacterial chemotaxis Lengeler et al. pp

Chemotaxis: responses E. coli –Makes temporal comparisons –Responds to spatial gradients –Compares environment of present with environment of past –Time: 1 to 2 sec

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

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……

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

Chemotaxis: components 4 receptor proteins Signal transduction proteins Adaptation proteins 4 receptors = methyl-accepting chemotaxis proteins (MCPs) span CM

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

Chemotaxis: components Signal transduction proteins CheA CheY CheW CheZ Adaptation proteins CheR CheB

MCPs NH TM highly variable sensory domain TM linker MH seq conservation; signaling domain MH COOH TM = transmembrane segment MH = methylated helix Sensory domain: periplasm Signaling domain: cytoplasm

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 His48  increase CheA~P

Excitation, cont’d –CheA~P + CheY  CheY~P Asp57 = tumble factor CheY~P binds to FliM of flagellar switch Signal = CW rotation = tumbling

–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

Signal transduction Adaptation CheR + CheB + MCPs [ATT] –converted into intracellular “short term memory” –registered as methylated MCP

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

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