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Infect Immun. 2016 Apr 22;84(5):1642-1649. doi: 10.1128/IAI.01562-15. Print 2016 May.

Binding of CFA/I Pili of Enterotoxigenic Escherichia coli to Asialo-GM1 Is Mediated by the Minor Pilin CfaE.

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Menzies Health Institute Queensland, School of Medical Sciences, Griffith University, Southport, QLD, Australia.
Institute for Future Environments and School of Earth, Environmental and Biological Sciences, Queensland University of Technology, Brisbane, QLD, Australia.
Medicinal Chemistry and Drug Action, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, VIC, Australia.
Menzies Health Institute Queensland, School of Medical Sciences, Griffith University, Southport, QLD, Australia
School of Pathology and Laboratory Medicine, University of Western Australia, Nedlands, WA, Australia.


CFA/I pili are representatives of a large family of related pili that mediate the adherence of enterotoxigenic Escherichia coli to intestinal epithelial cells. They are assembled via the alternate chaperone-usher pathway and consist of two subunits, CfaB, which makes up the pilus shaft and a single pilus tip-associated subunit, CfaE. The current model of pilus-mediated adherence proposes that CFA/I has two distinct binding activities; the CfaE subunit is responsible for binding to receptors of unknown structure on erythrocyte and intestinal epithelial cell surfaces, while CfaB binds to various glycosphingolipids, including asialo-GM1. In this report, we present two independent lines of evidence that, contrary to the existing model, CfaB does not bind to asialo-GM1 independently of CfaE. Neither purified CfaB subunits nor CfaB assembled into pili bind to asialo-GM1. Instead, we demonstrate that binding activity toward asialo-GM1 resides in CfaE and this is essential for pilus binding to Caco-2 intestinal epithelial cells. We conclude that the binding activities of CFA/I pili for asialo-GM1, erythrocytes, and intestinal cells are inseparable, require the same amino acid residues in CfaE, and therefore depend on the same or very similar binding mechanisms.

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