ARRA: A novel ternary virulence system in plague

Yersinia pestis is the causative agent of plague in humans. We have discovered a chromosomally located bicistronic operon that encodes novel pair of interacting surface proteins called YadS and YadC (collectively referred to as `Y'adB-C), that belong to the trirneric autotransporter family. YadB-C promotes invasion of epithelioid cells and J774A.1 macrophage-4ike cells; but unlike most trimeric autotransporters appears not to promote adherence. Interestingly, invasive activity requires the presence of the surface aspartyl protease Pta, which also is an adhesinlinvasin, independently of its protease activity. In addition, Pla selectively degrades YadB, causing YadB-C complexes to disappear, and its presence is required for release of a fragment of YadC into the culture medium. Like Pla, YadB-C is crucial for virulence in bubonic plague; however, it is not essential for virulence in pneumonic plague. This raises the possibility that the dominant virulence function of these proteins is directed against acute inflammation, which occurs rapidly in bubonic plague but only late in pneumonic plague. The small plasmid that encodes Pla is unique to Y. pestis, and its acquisition is believed to have been a key step in the evolution of Y. pestis from V. pseudotuberculosis. Thus yadBC may be another link to the high virulence of V. pest/s. We hypothesize that YadS, YadC, and Pla constitute a novel ternary virulence mechanism to counteract Inflammatory defenses that are mobilized early in bubonic plague. The goal of this proposed R2lproject is to define the essential roles of the 3 components of this system. In Aim 1 we will exploit a set of V. pestis strains carrying variants of these components to determine the roles of Pla, YadC, and YadB in YadB-C function in vitro. In Aim 2, we will characterize infections of normal mice and mice lacking key inflammatory cells to develop a hypothesis for the innate defense target of YadB-C.