The Yersinia pestis YscY protein directly binds YscX, a secreted component of the type III secretion machinery.

Human pathogenic yersiniae organisms export and translocate the Yop virulence proteins and V antigen upon contact with a eukaryotic cell. Yersinia pestis mutants defective for production of YscX or YscY were unable to export the Yops and V antigen. YscX and YscY were both present in the Y. pestis cell pellet fraction; however, YscX was also found in the culture supernatant. YscY showed structural and amino acid sequence similarities to the Syc family of proteins. YscY specifically recognized and bound to a region of YscX that included a predicted coiled-coil region. These data suggest that YscY may function as a chaperone for YscX in Y. pestis.