Evaluating the Role of the Fkpa Periplasmic Chaperone on the Secretion of the BrkA Autotransporter in Escherichia coli Strain K-12

Abstract

BrkA is a virulence factor of Bordetella pertussis, a causative agent of whooping cough, that can induce serum resistance and cell adhesion. As an autotransporter, BrkA is transported across the inner and outer membrane by using its N-terminal signaling sequence and C-terminal β-barrel, respectively. However, the detailed process of its translocation mechanism in the periplasm remains unknown. It has been observed that autotransporters keep their passenger domain in an unstable, non-native conformation while in the periplasm and only become stable once reaching the extracellular space. Studies have uncovered the interaction between periplasmic chaperones and autotransporters, suggesting they may play a role in their secretion across the periplasm. Current research has explored the roles of periplasmic chaperones like SurA, DegP, and Skp in the secretion of the BrkA autotransporter, but no available literature investigated the necessity of FkpA. FkpA interacts with the passenger domain of EspP, another T5SS autotransporter, suggesting that FkpA is necessary for BrkA secretion (1). We aimed to test this hypothesis by transforming wildtype (BW25113) and fkpA knockout (JW3309) Escherichia coli with pPALMB2 and pPALMC2 plasmids (2) and comparing the BrkA expression using western blot analysis. We captured a significant decrease in BrkA secretion from the western blot analysis, despite the presence of background noises, our data suggest that FkpA plays a role in BrkA secretion. Thus, we propose that FkpA is involved in facilitating the proper folding of the BrkA β-domain and maintaining a translocation-competent state.