Enteropathogenic Escherichia coli Virulence Factor Bundle-Forming Pilus Has a Binding Specificity for Phosphatidylethanolamine

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Abstract
The bundle-forming pilus (BFP) of enteropathogenic Escherichia coli (EPEC), an established virulence factor encoded on the EPEC adherence factor (EAF) plasmid, has been implicated in the formation of bacterial autoaggregates and in the localized adherence of EPEC to cultured epithelial cells. While understanding of the pathogenic mechanism of this organism is rapidly improving, a receptor ligand for BFP has not yet been identified. We now report, using both solid-phase and liposome binding assays, that BFP expression correlates with phosphatidylethanolamine (PE) binding. In a thin-layer chromatogram overlay assay, specific recognition of PE was documented for BFP-expressing strains, including E2348/69, a wild-type EPEC clinical isolate, as well as a laboratory strain, HB101, transformed with a bfp -carrying plasmid. Strains which did not express BFP did not bind PE, including a bfpA disruptional mutant of E2348/69, EAF plasmid-cured E2348/69, and HB101. E2348/69 also aggregated PE-containing liposomes but not phosphatidylcholine- or phosphatidylserine-containing liposomes, while BFP - negative strains did not produce aggregates with any tested liposomes. Purified BFP preparations bound commercial PE standards as well as a PE-containing band within lipid extracts from human epithelial cells and from E2348/69. Our results therefore indicate a specific interaction between BFP and PE and suggest that PE may serve as a BFP receptor for bacterial autoaggregation and may promote localized adherence to host cells, both of which contribute to bacterial pathogenesis.

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