Involvement of the DnaK-DnaJ-GrpE chaperone team in protein secretion in Escherichia coli.

We used depletion studies designed to further investigate the role of the DnaK, DnaJ, and GrpE heat shock proteins in the SecB-dependent and SecB-independent secretion pathways. Our previous finding that SecB-deficient strains containing the grpE280 mutation were still secretion proficient raised the possibility that GrpE was not involved in this secretory pathway. Using depletion studies, we now demonstrate a requirement for GrpE in this pathway. In addition, depletion studies demonstrate that while DnaK, DnaJ, and GrpE are involved in the secretion of the SecB-independent proteins (alkaline phosphatase, ribose-binding protein, and beta-lactamase), they are not the primary chaperones in this process.