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A plasmid-encoded prepilin peptidase gene from enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli, a leading agent of infantile diarrhea worldwide, adheres to tissue culture cells in a pattern called "localized adherence." Localized adherence is associated with bundle-forming pili encoded by the plasmid bfpA gene, the product of which is homologous with the major structural subunit proteins of type IV fimbriae in other bacteria. Several of these proteins have been shown to be processed from a precursor by a specific prepilin peptidase. We cloned restriction fragments downstream of the bfpA gene into an E. coli-Pseudomonas aeruginosa shuttle vector and mobilized them into a P. aeruginosa prepilin peptidase (pilD) mutant. A plasmid containing a 1.3-kb PstI-BamHI fragment was able to complement the pilD mutation, as demonstrated by restoration of sensitivity to the pilus-specific bacteriophage PO4. The DNA sequence of this fragment revealed an open reading frame, designated bfpP, the predicted product of which is homologous to other prepilin peptidases, including TcpJ of Vibrio cholerae (30% identical amino acids), PulO of Klebsiella oxytoca (29%), and PilD of P. aeruginosa (28%). A bfpA::TnphoA mutant complemented with a bfpA-containing DNA fragment only partially processes the BfpA protein. When complemented with a larger fragment containing bfpP as well as bfpA, the mutant expresses the fully processed BfpA protein. P. aeruginosa PAK, but not a pilD mutant of PAK, expresses mature BfpA protein when the bfpA gene is mobilized into this strain. Thus, as in other type IV fimbria systems, enteropathogenic E. coli utilizes a specific prepilin peptidase to process the major subunit of the bundle-forming pilus. This prepilin petidase contains sequence and reciprocal functional homologies with the PilD protein of P. aeruginosa.