Chaperone Caf1M stabilizes hybrid proteins containing sequences of F1 antigen subunit from Yersinia pestis

The Yersinia pestis (causative agent of plague) capsule antigen is a homopo lymer of Caf1 protein. Export of the subunits is mediated by the periplasmi c chaperone Caf1M. To study the mechanism of Caf1M activity, two hybrid gen es including coding sequences for the Caf1 signal peptide, human granulocyt e-macrophage colony-stimulating factor (GM-CSF) or interleukin-1 (IL-1) rec eptor antagonist, and mature Caf1 were constructed and expressed in Escheri chia coli. We have shown that in the absence of Caf1M the majority of Caf1 moieties within the hybrid proteins undergo proteolysis in the periplasmic space, presumably by the DegP protease. The coexpression of a gene for chap erone Caf1M significantly increased the amount of full-size hybrid proteins in the periplasm, probably as a result of stabilization of the subunit's s patial structure within the hybrid. This effect was not observed in JCB571 cells, which lack periplasmic disulfide isomerase DsbA, essential for Caf1M activity.