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Summary

Full virulence of Yersinia enterocolitica Biovar 1B requires two distinct and distantly related contact-dependent type III secretion (T3S) systems. The plasmid-encoded Ysc T3S system is essential for systemic stages of infection and the Yop effector proteins it translocates have been extensively studied. The chromosome-encoded Ysa T3S system contributes to gastrointestinal stages of infection, but the suite of Ysp effectors proteins it translocates into host cells remains obscure. Using a proteomics-based approach, the Ysa T3S system was analysed revealing a complex set of 15 secreted Ysp proteins. Seven of these proteins were previously described (YspA, YspB, YspC, YspD, YopE, YopN and YopP). Eight of these Ysps (YspK, YspI, YspE, YspF, YspP, YspY, YspN and YspL) had not previously been characterized. Several of the new Ysps are homologous to other virulence factors, including YspP with similarity to the Yersinia protein tyrosine phosphatase YopH and YspK with similarity to the Shigella serine/threonine kinase OspG. Biochemical analysis of purified hexa-histidine tagged YspK and YspP established that these proteins have kinase and phosphatase activity respectively. Infection of eukaryotic cells with Y. enterocolitica strains expressing a Ysp-CyaA chimeric protein resulted in Ysa T3S system-dependent increases in cytosolic levels of cAMP for six Ysps (YspK, YspI, YspE, YspF, YspP and YspL), but not two others (YspY and YspN). YspN, however, was required for translocation of effector proteins into eukaryotic cells by the Ysa T3S system. Competition assays in BALB/c mice revealed that mutants defective for the production of an individual Ysp are affected for colonization of gastrointestinal tissues. Collectively, the results of this study support the hypothesis that the Ysa T3S system targets a complex suite of effector proteins into host cells to affect the outcome of an infection. Identification of the suite of effectors delivered by the Ysa T3S system reveals that host cell signalling pathways are the probable targets of several Ysp effectors.