ZraP is a periplasmic molecular chaperone and a repressor of the zinc-responsive two-component regulator ZraSR

The bacterial envelope is the interface with the surrounding environment and is consequently subjected to a barrage of noxious agents including a range of compounds with antimicrobial activity. The ESR (envelope stress response) pathways of enteric bacteria are critical for maintenance of the envelope against these antimicrobial agents. In the present study, we demonstrate that the periplasmic protein ZraP contributes to envelope homoeostasis and assign both chaperone and regulatory function to ZraP from Salmonella Typhimurium. The ZraP chaperone mechanism is catalytic and independent of ATP; the chaperone activity is dependent on the presence of zinc, which is shown to be responsible for the stabilization of an oligomeric ZraP complex. Furthermore, ZraP can act to repress the two-component regulatory system ZraSR, which itself is responsive to zinc concentrations. Through structural homology, ZraP is a member of the bacterial CpxP family of periplasmic proteins, which also consists of CpxP and Spy. We demonstrate environmental co-expression of the CpxP family and identify an important role for these proteins in Salmonella's defence against the cationic antimicrobial peptide polymyxin B

New virulence-associated plasmid in Yersinia enterocolitica.

In a study of 103 strains of Yersinia enterocolitica, 10 strains were found to be lethal for mice and to possess 42- and 82-megadalton plasmids. This association was statistically significant (P much less than 0.001). Serotypes of Y. enterocolitica previously considered avirulent were found to possess these plasmids and to be lethal for mice. A spontaneous derivative of one strain contained only the 82-megadalton plasmid and was lethal for mice anyway. This virulence-associated plasmid is a potential diagnostic tool for the clinical or public health laboratory which must delineate pathogenic strains of Y. enterocolitica