Pili System

• pili are bacterial appendages involved in surface adherence and movement, act as molecular grappling hook by extending/retracting or polymerizing/depolymerizing from cell surface, conduct twitching motility

  
• bacteria can sense presence of solid surfaces and use type 4 pili (T4P) to attach to them, these pili are important for infection because bacteria need to adhere to epithelium to cause disease and avoid GI tract force

  
• T4P retraction/depolymerization generates the necessary force for movement by moving along a surface (twitching motility)

  
• the T4P is a dynamic cell surface appendage of different components:

  • PilA subunits polymerize to form pili structure and localize at inner membrane to be recognized by PilC
  • PilC is a 'platform' protein
  • PilB is an ATPase that provides energy for elongation through CW rotation of PilC
  • PilT is an ATPase that provides energy for retraction through CCW rotation of PilC

  
• the Chp chemosensory system regulates TWITCHING motility:

  • PilJ -> mechanical sensor that changes conformation and stimulates ChpA to auto phosphorylate and transfer to 3 RR
  • 1. PilG -> interacts with retracted T4P motor (PilB ATPase) to stimulate elongation in CW rotation
  • 2. PilH -> interacts with elongated T4P motor (PilT ATPase) to stimulate retraction in CCW rotation
  • 3. ChpB -> demethylase to sensitize to mechanical stress
  • PilK -> methylase to desensitize to mechanical stress

  
• studying twitching motility

  • phenotypic
  • twitching assays quantify the ability of piliated bacteria to move across a plastic surface covered by solid media
  • 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