title: The antibacterial toxin colicin N binds to the inner core of lipopolysaccharide and close to its translocator protein.
abstract: Colicins are a diverse family of large antibacterial protein toxins, secreted by and active against Escherichia coli and must cross their target cell's outer membrane barrier to kill. To achieve this, most colicins require an abundant porin (e.g. OmpF) plus a low-copy-number, high-affinity, outer membrane protein receptor (e.g. BtuB). Recently, genetic screens have suggested that colicin N (ColN), which has no high-affinity receptor, targets highly abundant lipopolysaccharide (LPS) instead. Here we reveal the details of this interaction and demonstrate that the ColN receptor-binding domain (ColN-R) binds to a specific region of LPS close to the membrane surface. Data from in vitro studies using calorimetry and both liquid- and solid-state NMR reveal the interactions behind the in vivo requirement for a defined oligosaccharide region of LPS. Delipidated LPS (LPS(Δ) (LIPID) ) shows weaker binding; and thus full affinity requires the lipid component. The site of LPS binding means that ColN will preferably bind at the interface and thus position itself close to the surface of its translocon component, OmpF. ColN is, currently, unique among colicins in requiring LPS and, combined with previous data, this implies that the ColN translocon is distinct from those of other known colicins.
authors.affiliation: Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, Newcastle University, Framlington Place, Newcastle-upon-Tyne, NE2 4HH, UK.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Johnson
authors.forename: Helen
authors.initials: H
authors.lastname: Ridley
authors.forename: Roberta
authors.initials: R
authors.lastname: Marchetti
authors.forename: Alba
authors.initials: A
authors.lastname: Silipo
authors.forename: David C
authors.initials: DC
authors.lastname: Griffin
authors.forename: Lucy
authors.initials: L
authors.lastname: Crawford
authors.forename: Boyan
authors.initials: B
authors.lastname: Bonev
authors.forename: Antonio
authors.initials: A
authors.lastname: Molinaro
authors.forename: Jeremy H
authors.initials: JH
authors.lastname: Lakey
mesh_terms: D002151:Calorimetry; D003087:Colicins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D018272:Porins / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D003087:Colicins; D008070:Lipopolysaccharides; C109237:OmpF protein; D018272:Porins