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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.