title: Crystal structures of the OmpF porin: function in a colicin translocon.
abstract: The OmpF porin in the Escherichia coli outer membrane (OM) is required for the cytotoxic action of group A colicins, which are proposed to insert their translocation and active domains through OmpF pores. A crystal structure was sought of OmpF with an inserted colicin segment. A 1.6 A OmpF structure, obtained from crystals formed in 1 M Mg2+, has one Mg2+ bound in the selectivity filter between Asp113 and Glu117 of loop 3. Co-crystallization of OmpF with the unfolded 83 residue glycine-rich N-terminal segment of colicin E3 (T83) that occludes OmpF ion channels yielded a 3.0 A structure with inserted T83, which was obtained without Mg2+ as was T83 binding to OmpF. The incremental electron density could be modelled as an extended poly-glycine peptide of at least seven residues. It overlapped the Mg2+ binding site obtained without T83, explaining the absence of peptide binding in the presence of Mg2+. Involvement of OmpF in colicin passage through the OM was further documented by immuno-extraction of an OM complex, the colicin translocon, consisting of colicin E3, BtuB and OmpF.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392, USA.
authors.forename: Eiki
authors.initials: E
authors.lastname: Yamashita
authors.forename: Mariya V
authors.initials: MV
authors.lastname: Zhalnina
authors.forename: Stanislav D
authors.initials: SD
authors.lastname: Zakharov
authors.forename: Onkar
authors.initials: O
authors.lastname: Sharma
authors.forename: William A
authors.initials: WA
authors.lastname: Cramer
mesh_terms: D001665:Binding Sites; D003087:Colicins / Q000737:chemistry* / Q000378:metabolism; D003460:Crystallization; D015640:Ion Channel Gating; D008274:Magnesium / Q000737:chemistry*; D008958:Models, Molecular; D010455:Peptides / Q000378:metabolism; D018272:Porins / Q000737:chemistry* / Q000502:physiology; D011485:Protein Binding; D011487:Protein Conformation; D021381:Protein Transport
chemical_list: D003087:Colicins; C109237:OmpF protein; D010455:Peptides; D018272:Porins; D008274:Magnesium