Table 1.

Proteins which are secreted via the type III secretion pathway

OrganismSecreted proteina(reference)Biochemical activity; interaction with host or other proteinsEffect on host cell; functionRemarks
Yersinia spp.YopE, 219 (131)Cytotoxic, F-actin disruptionTranslocated
YopH, 468 (59,305)PTPase dephosphorylates paxillin, FAK, p130c a s Inhibition of phagocytosisTranslocated
YpkA, 732 (149)Protein serine/threonine kinaseTranslocated
YopM, 367 (56, 269)Binds to thrombinTranslocated
YopJ/P, 264/288 (150,313)Induction of apoptosis in macrophagesSimilar to plant pathogen AvrX and AvrA from S. typhimurium
YopR, 165 (14, 307)
YopB, 401 (173)Pore-forming translocaseTranslocation
YopD, 306 (173)Translocation
YopK, 182 (206)Modulation of translocation efficiency
YopN, 293 (129,454)Putative surface sensor, regulation of secretion
LcrV, 326 (41, 343, 359)Suppression of immune responseAlso regulatory function
LcrG, 95 (41,359)Regulation of secretion
LcrQ/YscM1/YscM2, 115 (307, 370, 422)Involved in feedback transcriptional regulation
P. aeruginosa ExoS, 453 (253)ADP-ribosyltransferaseCytotoxic, F-actin disruption
ExoT, 457ADP-ribosyltransferase
ExoU, 687 (120)Cytotoxic
PcrV, 294 (493)
PopB, 392 (493)Translocation (?)
PopD, 295 (493)Translocation (?)
PopN, 288 (493)Regulation of secretion (?)
S. flexneri IpaB, 580 (450)Binds to α5β1 integrin and to ICE proteaseInduction of membrane ruffling, phagosomal lysis, induction of apoptosisAdditional function in regulation of secretion
IpaC, 382 (450)Binds to α5β1 integrinInduction of membrane ruffling, phagosomal lysis
IpaD, 332 (450)Binds to α5β1 integrinCell invasion, phagosomal lysisRegulation of secretion
IpaA, 633 (451)Binds to vinculinModulation of cell invasion
VirA, 400 (443)Intercellular spread
S. typhimurium SPI-1AvrA, 302 (183)
Sip/SspB, 593 (234)Cell invasion, induction of apoptosisTranslocation
Sip/SspC, 409 (216,234)Cell invasion, induction of apoptosisTranslocation
Sip/SspD, 338 (216,233)Cell invasion, induction of apoptosisTranslocation, regulation of secretion (?)
Sip/SspA, 684 (233)
SopB, 561 (151)Involved in intestinal transepithelial signalling, translocated
SopE, 240 (485)Translocated
SptP, 544 (235)PTPase
EPECEspA, 198 (242)A/E lesion formation
EspB, 321 (104)A/E lesion formation
EspC, 381 (259)A/E lesion formation
Tir, 549 (239)Binds to EPEC intiminReceptor for EPEC attachmentInserted in eukaryotic cell membrane, modified by tyrosine phosphorylation
P. syringae AvrPtob, 164 (390)Binds to Pto kinaseElicitation of HRHost range determination, translocated (?)
HrpA, 113 (357)Structural component of Hrp pilus
HrpZ, 341 (188)Elicitation of HR
E. amylovora HrpN, 385 (472)Elicitation of HR
R. solanacearum PopA1, 344 (26)Elicitation of HR
  • a The size of the protein in amino acids is shown after the protein name. See text for further details and references.

  • b Many more Avr proteins from various plant pathogens (recently summarized in reference 455) have been cloned and might be secreted and translocated via type III secretion pathways.