Loss of the Chaperone FkpA and Repeated Subculturing Weakens BrkA Autotransporter Secretion in Escherichia coli

Abstract

Bordetella resistance to killing (BrkA) is a type V secretion system (T5SS) autotransporter and virulence factor of Bordetella pertussis. It contributes to serum resistance, host cell adhesion, and is secreted across the inner and outer membranes by its own N-terminal signal sequence and C-terminal β-barrel domain. During periplasmic transit, BrkA must remain in an unfolded, secretion-competent state, before folding into its functional form at the cell surface. This process is thought to be facilitated by periplasmic chaperone proteins, though the precise molecular mechanisms remain unknown. To build upon prior research suggesting a role of FkpA in this pathway, we further investigated its contribution using a genetically validated fkpA knockout Escherichia coli model. Our results suggest that while FkpA supports BrkA folding and maturation, its absence can be compensated for by other chaperones, and that passage history is a critical factor affecting protein secretion. This work highlights the complex interplay between periplasmic chaperones and expression conditions in modulating BrkA secretion, offering insight into the broader network of factors influencing autotransporter biogenesis.