title: EtpB is a pore-forming outer membrane protein showing TpsB protein features involved in the two-partner secretion system.
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 beta-barrel domain that is occluded by an N-terminal alpha-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 beta-barrel conformation and indicate that EtpB presents typical features of the OM TpsB proteins.
authors.affiliation: Centre de Biochimie Structurale, CNRS UMR 5048, Université Montpellier 1, Montpellier, France.
authors.forename: Albano C
authors.initials: AC
authors.lastname: Meli
authors.forename: Maria
authors.initials: M
authors.lastname: Kondratova
authors.forename: Virginie
authors.initials: V
authors.lastname: Molle
authors.forename: Laurent
authors.initials: L
authors.lastname: Coquet
authors.forename: Andrey V
authors.initials: AV
authors.lastname: Kajava
authors.forename: Nathalie
authors.initials: N
authors.lastname: Saint
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003198:Computer Simulation; D004591:Electrophoresis, Polyacrylamide Gel; D004594:Electrophysiology; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; C510012:EtpB protein, E coli; D008051:Lipid Bilayers