Expression of Truncated SurA Potentially Disrupts BrkA Maturation in Escherichia coli

Abstract

SurA is a highly conserved chaperone protein involved in the folding and translocation of outer membrane proteins in gram-negative bacteria. One such family of proteins that rely on SurA for delivery to the β-barrel assembly machinery complex for insertion into the outer membrane is the type Va autotransporter family. These proteins are responsible for a variety of functions. For example, BrkA in Bordetella pertussis has roles in cell adhesion and virulence. The maturation of BrkA involves proper folding in the periplasm and cleavage of its passenger domain. However, the exact mechanism by which SurA facilitates BrkA expression remains unclear. Previous studies investigating this interaction have not yet determined whether SurA is sufficient to rescue BrkA expression in a complementation experiment using a SurA knockout strain. This study originally aimed to engineer such a plasmid and evaluate its efficacy by analyzing cleaved and uncleaved BrkA expression patterns. The p2bCAAT plasmid was constructed by inserting a surA gene segment into the BrkA-containing pPALMC1, which was then transformed into SurA-knockout Escherichia coli cells. However, due to a mistake in the insert, the plasmid had an incomplete surA gene segment. Interestingly, western blot analysis revealed that p2bCAAT not only failed to rescue the wildtype BrkA phenotype in knockout cells, but also caused the wildtype strain to exhibit a BrkA expression pattern resembling that of the knockout strain. Our results suggest that the truncated SurA may have disrupted endogenous SurA function and consequently BrkA maturation. This study provides further support on the potentially important interactions between SurA and BrkA.