Loss of BamE Increases Susceptibility of the BrkA Passenger Domain to Proteolytic Degradation in Escherichia coli

Abstract

Bordetella pertussis, a Gram-negative bacterium that causes whooping cough, utilizes Bordetella resistance-to-killing (BrkA), a Type V_a autotransporter, to mediate resistance to killing by the complement pathway and cause disease. BrkA comprises a passenger α-domain that is secreted and a translocator domain that forms a β-barrel pore in the outer membrane, allowing for the passenger's secretion. The assembly of this β-barrel requires the β–barrel–assembly machinery complex, which includes the BamE protein. Although BamE was previously considered non-essential for the secretion of autotransporters such as SadA and Pet, conflicting evidence suggests that it may influence BrkA secretion. To further elucidate the role of BamE in BrkA secretion, we investigated the effect of BamE on the stability of BrkA in ∆bamE knockout and wild-type Escherichia coli cells. Through a series of trypsin susceptibility assays, we show that the BrkA passenger domain displays increased susceptibility to proteolytic degradation. These findings suggest that BamE contributes to the stability of the BrkA passenger domain.