[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 homopolymer of Caf1 protein. Export of the subunits is mediated by the periplasmic chaperone Caf1M. To study the mechanism of Caf1M activity, two hybrid genes including coding sequences for the Caf1 signal peptide, human granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-1 (IL-1) receptor antagonist, and mature Caf1 were constructed and expressed in Escherichia 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 chaperone Caf1M significantly increased the amount of full-size hybrid proteins in the periplasm, probably as a result of stabilization of the subunits spatial structure within the hybrid. This effect was not observed in JCB571 cells, which lack periplasmic disulfide isomerase DsbA, essential for Caf1M activity.