pili (part 2)

Not complete yet! (Need to check them over again)

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Type IV pili

• Most wide-spread.
• Found in 
  • many g(-) 
    • EPEC, 
    • EHEC, 
    • Salmonella enterica, 
    • Pseudomonas aeruginosa, 
    • Legionella pneumophila, 
    • Neisseria gonorrhoeae, 
    • Neisseria meningitidis, 
    • Vibrio cholerae
  • two g(+):
    
    • Clostridium sp.
    • Ruminococcus sp.
  • Cyanobacteria.
• Characteristics
  • 6-8 nm (wide), many micrometers (long).
  • flexible.
  • often aggregate to form bundles.
  • usually homopolymers of pilins (15-20 kDa).
  • some have an adhesive subunit at the tip.
  • prepilins (precursors with a leader peptide).
  • retraction ATPase : depolymerization of pilus fiber.
• Functions
  • cell adhesion
  • biofilm formation
  • DNA uptake (transformation)
  • phage transduction
  • twitching motility (flagella-independent, retract generating mechanical force).
  • nanowires for extracellular electron transfer (in Geobacter sulfurreducens).
• Classified
  • Type IVa (<10-residue leader peptide & 150-160 residue mature protein).
    • Neisseria pilus 
      • gonococcal (GC) pilus in N. gonorrhoeae & meningococcal (MC) pilus in N. meningitidis
      • GC/MC pili binds to non-ciliated host cells in mucosa. (Its receptor is membrane cofactor protein, MCP.)
      • PilE (major pilin)
      • PilC (adhesin at pilus tip)
      • PilT (ATPase in inner mb, for pilus retraction & elongation, for DNA transformation)
      • PilX (pilin-like protein, for aggregate formation &adhesion)
    • Ps. aeruginosa pilus
      • extend as bundles from one or both of the cell poles.
      • functions: 
        • colonization, 
        • twitching motility, 
        • biofilm formation, 
        • bacteriophage infection, & 
        • natural transformation.
      • PAK pili (strain K pili) & PAO pili (strain O pili)
      • its receptor is b-GalNAc(1-4)bGal moiety of glycolipids asialo-GM1 & asialo-GM2 on epithelial cells.
      • PilA (adhesin, at tip)
  • Type IVb (35-40-residue leader peptide & 180-200-residue (40-50 residue) mature protein.
    • in bacteria infecting human intestinal track
      • EPEC (major cause of infant diarrhoea)
      • ETEC
      • Salmonella typhi
      • Vibrio cholerae
    • Bundle-forming pilus (BFP) of EPEC
      • able to associate & form intertwined rope-like aggregates (15 microns long, polar localization)
      • colonization
      • Bundlin is major pilin (encoded by plasmid-borne bfpA)
    • Toxin co-regulated pilus (TCP) of V. cholerae
      • colonize human small intestinal mucosa.
      • homopolymer of TcpA pilins.
      • polar localization
      • 15 microns long, self-aggregate
      • tcp gene is in an operon located on 39kbp Vibrio pathogenicity island (VPI)
• Assembly
  • 12 or more proteins.
  • pilin (major subunit)
  • prepilin peptidase (inner membrane).
  • specific ATPase.
  • inner membrane protein recruiting cytoplasmic ATPase.
  • secretin (outer membrane)
  • have homologues in type II secretion & archeal flagella systems.