Table 2.

Proteins secreted by the SPI1 type III secretion system

ProteinHost cell localizationaFunctionbHomologuesc
SipASurfaceNDd IpaA (Shigella)
SipBIntracellularTranslocation? Apoptosis?IpaB (Shigella), EspD (EPECe), EspB (EHECe), Pep/PopB (Pseudomonas aeruginosa)
SipCIntracellularTranslocation?IpaC (Shigella)
SipDExtracellularTranslocation?IpaD (Shigella)
InvJ/SpaNNDSecretionSpaN (Shigella)
SpaONDSecretionSpaO (Shigella); YscQ (Yersinia); FliNf
SptPIntracellularCytoskeletal disruption; splenic colonizationYopE, ExoS (N-term.); YopH (C-term.)
SopEIntracellularCytoskeletal reorganization; invasionNone identified
SigD/SopBIntracellularInvasion; transepithelial signaling of PMNsIpgD (Shigella)
AvrAIntracellularNDYopJ/YopP (Yersinia); AvrAxc (Xanthamonas)
  • a Localization of the secreted protein with respect to the eucaryotic host cell.

  • b ? indicates that the location of these proteins with respect to the host cell has not been determined.

  • c Homologues listed have significant sequence and/or functional similarity to the respective Salmonellaprotein.

  • d ND, not determined.

  • e EHEC, enterohemorrhagic E. coli; EPEC, enteropathogenic E. coli.

  • f FliN, “flagellar motor switch protein” from E. coli, S. typhimurium, Caulobacter crescentus, and several other gram-negative bacteria.