title: Crystal structure of the cytotoxic bacterial protein colicin B at 2.5 A resolution.
abstract: Colicin B (55 kDa) is a cytotoxic protein that recognizes the outer membrane transporter, FepA, as a receptor and, after gaining access to the cytoplasmic membranes of sensitive Escherichia coli cells, forms a pore that depletes the electrochemical potential of the membrane and ultimately results in cell death. To begin to understand the series of dynamic conformational changes that must occur as colicin B translocates from outer membrane to cytoplasmic membrane, we report here the crystal structure of colicin B at 2.5 A resolution. The crystal belongs to the space group C2221 with unit cell dimensions a = 132.162 A, b = 138.167 A, c = 106.16 A. The overall structure of colicin B is dumbbell shaped. Unlike colicin Ia, the only other TonB-dependent colicin crystallized to date, colicin B does not have clearly structurally delineated receptor-binding and translocation domains. Instead, the unique N-terminal lobe of the dumbbell contains both domains and consists of a large (290 residues), mostly beta-stranded structure with two short alpha-helices. This is followed by a single long ( approximately 74 A) helix that connects the N-terminal domain to the C-terminal pore-forming domain, which is composed of 10 alpha-helices arranged in a bundle-type structure, similar to the pore-forming domains of other colicins. The TonB box sequence at the N-terminus folds back to interact with the N-terminal lobe of the dumbbell and leaves the flanking sequences highly disordered. Comparison of sequences among many colicins has allowed the identification of a putative receptor-binding domain.
authors.affiliation: Department of Chemistry and School of Molecular Biosciences, Washington State University, Pullman, WA 99164, USA.
authors.forename: Jacqueline L
authors.initials: JL
authors.lastname: Hilsenbeck
authors.forename: HaJeung
authors.initials: H
authors.lastname: Park
authors.forename: Gregory
authors.initials: G
authors.lastname: Chen
authors.forename: Buhyun
authors.initials: B
authors.lastname: Youn
authors.forename: Kathleen
authors.initials: K
authors.lastname: Postle
authors.forename: ChulHee
authors.initials: C
authors.lastname: Kang
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D003087:Colicins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D002352:Carrier Proteins; D003087:Colicins; D011956:Receptors, Cell Surface; C029489:enterobactin receptor