EtpB Is a Pore-Forming Outer Membrane Protein Showing TpsB Protein Features Involved in the Two-Partner Secretion System |
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Authors: | Albano C. Meli Maria Kondratova Virginie Molle Laurent Coquet Andrey V. Kajava Nathalie Saint |
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Affiliation: | 1.Centre de Biochimie Structurale, CNRS UMR 5048,Université Montpellier 1 et 2,Montpellier,France;2.INSERM U554,Montpellier,France;3.Centre de Recherches de Biochimie Macromoleculaire, CNRS UMR 5237,Université Montpellier 1 et 2,Montpellier cedex 5,France;4.Institut de Biologie et de Chimie des Protéines,Université de Lyon, CNRS UMR 5086,Lyon,France;5.UMR 6522 CNRS, PBM, Plate-forme Protéomique IFRMP23,Université de Rouen,Mont-Saint-Aignan,France |
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Abstract: | Attachment to host tissues is a critical step in the pathogenesis of most bacterial infections. Enterotoxigenic Escherichia coli (ETEC) remains one of the principal causes of infectious diarrhea in humans. The recent identification of additional ETEC surface molecules suggests that new targets may be exploited in vaccine development. The EtpA protein identified in ETEC H10407 is a large glycosylated adhesin secreted via the two-partner secretion system. EtpA requires its putative partner EtpB for translocation across the outer membrane (OM). We investigated the biochemical and electrophysiological properties of purified EtpB. We showed that EtpB is 65-kDa heat-modifiable protein localized to the OM. Electrophysiological experiments indicated that EtpB is able to form pores in planar lipid bilayer membranes with an asymmetric current, suggesting its functional asymmetry. The pore of EtpB frequently assumes an opened conformation and fluctuates between three well-defined conductance states. In silico analysis of the EtpB amino acid sequence and molecular modeling suggest that EtpB is similar to the well-known TpsB protein FhaC from Bordetella pertussis and has a C-terminal transmembrane β-barrel domain that is occluded by an N-terminal α-helix, an extracellular loop, and two periplasmic polypeptide-transport-associated (POTRA) domains. Together, these data confirm that EtpB is a pore-forming protein mainly folded into a β-barrel conformation and indicate that EtpB presents typical features of the OM TpsB proteins. |
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