title: Colicin N binds to the periphery of its receptor and translocator, outer membrane protein F.
abstract: Colicins kill Escherichia coli after translocation across the outer membrane. Colicin N displays an unusually simple translocation pathway, using the outer membrane protein F (OmpF) as both receptor and translocator. Studies of this binary complex may therefore reveal a significant component of the translocation pathway. Here we show that, in 2D crystals, colicin is found outside the porin trimer, suggesting that translocation may occur at the protein-lipid interface. The major lipid of the outer leaflet interface is lipopolysaccharide (LPS). It is further shown that colicin N binding displaces OmpF-bound LPS. The N-terminal helix of the pore-forming domain, which is not required for pore formation, rearranges and binds to OmpF. Colicin N also binds artificial OmpF dimers, indicating that trimeric symmetry plays no part in the interaction. The data indicate that colicin is closely associated with the OmpF-lipid interface, providing evidence that this peripheral pathway may play a role in colicin transmembrane transport.
authors.affiliation: The Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle-upon-Tyne, NE2 4HH, United Kingdom.
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Baboolal
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Conroy
authors.forename: Katrina
authors.initials: K
authors.lastname: Gill
authors.forename: Helen
authors.initials: H
authors.lastname: Ridley
authors.forename: Virak
authors.initials: V
authors.lastname: Visudtiphole
authors.forename: Per A
authors.initials: PA
authors.lastname: Bullough
authors.forename: Jeremy H
authors.initials: JH
authors.lastname: Lakey
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D003087:Colicins / Q000737:chemistry* / Q000378:metabolism*; D003460:Crystallization; D019281:Dimerization; D004583:Electrons; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D008070:Lipopolysaccharides / Q000737:chemistry / Q000378:metabolism; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism; D008954:Models, Biological; D008958:Models, Molecular; D018272:Porins / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism
chemical_list: D003087:Colicins; D029968:Escherichia coli Proteins; D008070:Lipopolysaccharides; D008563:Membrane Lipids; C109237:OmpF protein; D018272:Porins; D011956:Receptors, Cell Surface; C028593:colicin receptor, E coli