bfpB

bfpB is a gene in Enteroaggregative Escherichia coli (EAEC) that is part of the bundle-forming pilus (BFP) operon located on the virulence plasmid pAA. In the standard model of the operon, bfpA encodes the major pilin subunit, while bfpB is the outer membrane usher protein required for pilus assembly, and bfpC functions as a periplasmic chaperone. The BFP is a type of fimbrial structure that promotes initial adherence to intestinal mucosa and the formation of bacterial microcolonies, contributing to EAEC’s attachment and colonization.

Function and assembly: The bfpB-encoded usher protein forms a channel in the outer membrane that guides pilus subunits to assemble into the extracellular pilus fiber via the chaperone-usher pathway. This process involves the coordinated action of pilin subunits delivered by the periplasmic chaperone (including the product of bfpC) and their orderly assembly at the usher to produce functional bundle-forming pili on the bacterial surface. Disruption of bfpB can impair BFP assembly, reducing adherence and aggregation in vitro and attenuating colonization in experimental models.

Regulation and significance: Expression of the bfp operon is positively regulated by AggR, a global virulence regulator in EAEC, and is influenced by environmental conditions. As a component of the BFP assembly system, bfpB contributes to EAEC’s ability to form biofilms and establish intestinal colonization, making it a subject of interest in studies of EAEC pathogenicity and potential therapeutic targeting.

See also: bundle-forming pilus, AggR, Enteroaggregative Escherichia coli, virulence plasmid pAA.