Chaperone Protein BamB Directly Supports BrkA Translocation and Folding in Escherichia coli

Abstract

Autotransporters are virulence factors expressed on the surface of gram-negative bacteria as part of the type V secretion system. As the name suggests, the surface expression of an autotransporter is facilitated by passage through the protein’s own translocation domain, rather than an additional channel. One such example is BrkA of Bordetella pertussis, a type V autotransporter responsible for adhesion, serum resistance, and cellular invasion. The assistance of chaperone proteins is required to translocate autotransporters across bacterial membranes and enable proper folding into functional structures on the cell surface. However, the exact chaperones required for BrkA surface expression are currently unclear. In this study, a panel of Escherichia coli chaperone knockout strains was transformed with a brkA expression vector to investigate the importance of these chaperones in stable autotransporter surface expression. Through trypsin accessibility assays and western blot analysis we found that BamB may be for the expression of cleaved BrkA on the outer membrane, and may directly interact with the protein during this process. We used cross-linking experiments and found that BamB may directly interact with BrkA autotransporter. This project aims to characterize the functional significance of a wide panel of chaperones with respect to BrkA. Insights derived from this study are relevant to immunotherapeutic and vaccine development, where BrkA is an attractive target due to its surface presentation and its role as a virulence factor.