Flagellar System

• flagella is a protein machine for propelling bacteria through aqueous environment to perform swimming motility, responds to nutrient signals, bacteria can be mono/peri -trichous

  
• the flagella has 3 core components:

  • basal body -> anchors flagella to cell envelope
  • hook -> connects basal body to filament
  • filament -> long polymer comprised of flagellin subunits

  rotates in 2 directions CW (tumble) and CCW (run)

  
• the basal body has to critical components which control flagellar rotation

  • C Ring
  • FliM

  
• 2 modes of SWIMMING motility by flagella are running and tumbling

  • no nutrients -> bacteria tumble to sample surroundings
  • nutrients present -> bacteria run towards higher nutrient concentrations

  *running function is not unidirectional or linear, it's all over the place

  ALSO run = CCW, tumble = CW
• flagellar movement:

  run = CCW, tumble = CW
• flagellar swimming motility is not LINEAR, it tumbles every now and then while running to RESAMPLE its environment

  
• a chemosensory pathway known as the Che system controls flagellar rotation, CW/CCW rotation depends on:

  • presence of phosphorylated CheY binding to the basal body (C ring and FliM) = CW, tumble
  • no P~CheY = CCW, run

  
• Che system for swimming motility:

  • methyl accepting chemotaxis proteins (MCP) -> chemoreceptor proteins
  • CheW -> adaptor between MCP and CheA
  • CheA -> sensory kinase protein, auto phosphorylates then transfers to CheY and CheB
  • CheZ -> phosphatase for CheY and CheA
  • CheY -> when phosphorylated, binds basal body of flagella at FliM/C ring to tumble (RR)
  • CheR -> constitutively active methyltransferase that methylates MCPs
  • CheB -> when phosphorylated, functions as methylesterase that demethylates MCP to sensitize to nutrients

  **MCP + CheW + CheA = HK

  
• Che system for swimming motility:

  • methyl accepting chemotaxis proteins (MCP) -> chemoreceptor proteins
  • CheW -> adaptor between MCP and CheA
  • CheA -> sensory kinase protein, auto phosphorylates then transfers to CheY and CheB

  **MCP + CheW + CheA = HK

  
• Che system for swimming motility:

  • CheZ -> phosphatase for CheY and CheA

  
• Che system for swimming motility:

  • CheY -> when phosphorylated, binds basal body of flagella at FliM/C ring to tumble (RR)

  
• Che system for swimming motility:

  • CheR -> constitutively active methyltransferase that methylates MCPs
  • CheB -> when phosphorylated, functions as methylesterase that demethylates MCP to sensitize to nutrients (RR)

  
• the 4 types of MCP commonly found in E. coli is Tsr, Tar, Trg, Tap

  • N terminal sensor domains that bind multiple ligands and respond to different signals (attractant/repellant)
  • all transmembrane proteins
  • C terminal cytoplasmic domain is homologous between MCP
• Che system TUMBLING in absence of nutrients

  • MCP not bound to anything (signal) -> CheA auto phosphorylates -> transfers Pi to CheY and CheB ==>
  • CheY ~P interacts with basal body -> CCW to CW rotation -> tumble
  • CheB ~P ensures MCP is DEmethylated or low on methylation -> ensures MCP signals to CheA so cycle repeats
  • ***bacteria continues to tumble until they enter nutrient gradient

  
• Che system turned off thus RUNNING in presence of nutrients

  • MCP bound to nutrients -> this inhibits CheA from auto phosphorylating
  • CheZ performs phosphatase function on CheY
  • CheB function (demethylation) is low thus CheR methylates MCP and forces CheA on after a while independent if nutrients are present or not because the bacteria has to RESAMPLE the environment -> built in negative feedback loop to ensure a unidirectional system samples 3D space

  
• The Che system is ON when tumbling (CW) and OFF when running (CCW)
• studying chemotaxis

  • phenotypic
  • swimming/motility assays quantify the ability of bacteria to move through semi solid media containing chemical attractant
  • western blot analysis
  • monitors covalent modification of proteins
  • can use antibodies to see methylation levels of MCP or other components that get methylated, same thing with phosphorylation

  
• swarming motility describes flagellar movement across a solid surface and requires increased cell/cell contact and production of surfactant