Table 2

Examples of effector proteins of known function secreted via type III secretion systems.

Bacterial speciesSecreted proteinBiochemical activityEffect on host cell function
Animal pathogens
Enteropathogenic E. coli TirReceptor for intiminEffacement of the microvilli of the intestinal brush border
P. aeruginosa cytotoxicityExoSADP-ribosyltransferaseInhibition of phagocytosis
ExoYAdenylate cyclaseCytotoxicity
S. typhimuriumSopEExchange factor for Rho GTPases (such as CDC42 and Rac)Actin cytoskeleton reorganization; activation of MAP kinase pathways
SopB (SigA)Inositol phosphate phosphataseActin cytoskeleton reorganization; stimulation of Clsecretion
SipABinds actin, lowering its critical concentration and stabilizing F-actinPromotes localized actin cytoskeleton reorganization
SptPTyrosine phosphataseReorganization of the actin cytoskeleton
Shigella spp.IpaBActivation of caspase-1; binds β1-integrins and CD44Apoptosis
IpaABinds vinculinStimulation of bacterial entry
IpgDPutative inositol phosphate phosphataseUnknown
Yersinia spp.YopEUnknownDisruption of the actin cytoskeleton; inhibition of phagocytosis
YopHTyrosine phosphataseDisruption of focal adhesions; inhibition of phagocytosis
YpkASerine/threonine kinaseUnknown
YopJ (YopP)UnknownApoptosis
Plant pathogens
P. syringae pv. tomato AvrPtoInteracts with Pto (R gene product); activates Pto serine/threonine kinase signaling pathwayHR
Xanthomonas campestris pv. vesicatoriaAvrBs2Interacts with Bs2 R gene product of resistant pepper cultivars; sequence predicts ability to synthesize or hydrolyze phosphodiester linkages, which may be involved in its virulence functionHR
X. campestris pv.vesicatoria AvrBs3 familyLocalized to plant nuclei; probable transcription factors; activity determined by multiple repeats of 34 amino–acid sequenceHR