YOPK OF YERSINIA-PSEUDOTUBERCULOSIS CONTROLS TRANSLOCATION OF YOP EFFECTORS ACROSS THE EUKARYOTIC CELL-MEMBRANE

Introduction of anti-host factors into eukaryotic cells by extracellul ar bacteria is a strategy evolved by several Gram-negative pathogens. In these pathogens, the transport of virulence proteins across the bac terial membranes is governed by closely related type ill secretion sys tems. For pathogenic Yersinia, the protein transport across the eukary otic cell membrane occurs by a polarized mechanism requiring two secre ted proteins, YopB and YopD. YopB was recently shown to induce the for mation of a pore in the eukaryotic cell membrane, and through this por e, translocation of Yop effectors is believed to occur (Hakansson et a l., 1996b). We have previously shown that YopK of Yersinia pseudotuber culosis is required for the development of a systemic infection in mic e. Here, we have analysed the role of YopK in the virulence process in more detail. A yopK-mutant strain was found to induce a more rapid Yo pE-mediated cytotoxic response in HeLa cells as well as in MDCK-1 cell s compared to the wild-type strain. We found that this was the result of a cell-contact-dependent increase in translocation of YopE into HeL a cells. In contrast, overexpression of YopK resulted in impaired tran slocation. In addition, we found that YopK also influenced the YopB-de pendent lytic effect on sheep erythrocytes as well as on HeLa cells. A yopK-mutant strain showed a higher lytic activity and the induced por e was larger compared to the corresponding wild-type strain, whereas a strain overexpressing YopK reduced the lytic activity and the apparen t pore size was smaller. The secreted YopK protein was found not to be translocated but, similar to YopB, localized to cell-associated bacte ria during infection of HeLa cells. Based on these results, we propose a model where YopK controls the translocation of Yop effecters into e ukaryotic cells.