Chaperone Protein BamE Supports BrkA Secretion and Membrane Stability

Abstract

Gram-negative bacteria have evolved a diverse array of secretion systems to transport proteins across cell membranes and into the extracellular environment. BrkA is a virulence factor in Bordetella pertussis, the causative agent of whooping cough, that contributes to serum resistance, adhesion, and immune evasion. As a type V_a autotransporter, BrkA is transported across the inner membrane to the surface, facilitated by auto-proteolysis within the periplasmic space. Proper folding and surface expression of BrkA requires support from several periplasmic and outer membrane associated chaperone proteins. BamE is an outer membrane associated protein and a non-essential component of the heteropentomeric BAM complex. In this study, we aim to characterize the contributions of BamE to BrkA expression, membrane stability, and growth rate. Using an Escherichia coli bamE knockout model, transformed with a BrkA expression vector, we show that BamE supports proper cleavage of BrkA for extracellular presentation and expression. Through EDTA minimum inhibitory concentration and growth curve assay, we found that the absence of this BAM complex protein impairs membrane stability while increasing growth rate. Our findings further characterize the role of the BAM complex in autotransporter folding.