YSCB OF YERSINIA-PESTIS FUNCTIONS AS A SPECIFIC CHAPERONE FOR YOPN

Following contact with a eucaryotic cell, Yersinia species pathogenic for humans (Y. pestis, Y, pseudotuberculosis, and Y. enterocolitica) e xport and translocate a distinct set of virulence proteins (YopE, YopH , YopJ, YopM, and YpkA) from the bacterium into the eucaryotic cell. D uring in vitro growth at 37 degrees C in the presence of calcium, Yop secretion is blocked; however, in the absence of calcium, Yop secretio n is triggered. Yop secretion occurs via a plasmid-encoded type III, o r ''contact-dependent'' secretion system. The secreted YopN (also know n as LcrE), TyeA, and LcrG proteins are necessary to prevent Yop secre tion in the presence of calcium and prior to contact with a eucaryotic cell. In this paper we characterize the role of the yscB gene product in the regulation of Yop secretion in Y. pestis. A yscB deletion muta nt secreted YopM and V antigen both in the presence and in the absence of calcium; however, the export of YopN was specifically reduced in t his strain. Complementation with a functional copy of yscB in trans co mpletely restored the wild-type secretion phenotype for YopM, YopN, an d V antigen. The YscB amino acid sequence showed significant similarit ies to those of SycE and SycH, the specific Yop chaperones for YopE an d YopH, respectively. Protein cross-linking and immunoprecipitation st udies demonstrated a specific interaction between YscB and YopN. In-fr ame deletions in yopN eliminating the coding region for amino acids 51 to 85 or 6 to 100 prevented the interaction of YopN with YscB. Taken together, these results indicate that YscB functions as a specific cha perone for YopN in Y. pestis.