Yersinia pestis YscG Protein Is a Syc-Like Chaperone That Directly Binds YscE

Pathogenic Yersinia species secrete virulence proteins, termed Yersinia outer proteins (Yops), upon contact with a eukaryotic cell. The secretion machinery is composed of 21 Yersinia secretion (Ysc) proteins. Yersinia pestis mutants defective in expression of YscG or YscE were unable to export the Yops. YscG showed structural and limited amino-acid-sequence similarities to members of the specific Yop chaperone (Syc) family of proteins. YscG specifically recognized and bound YscE; however, unlike previously characterized Syc substrates, YscE was not exported from the cell. These data suggest that YscG functions as a chaperone for YscE.