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    EMBO J. 2008 Aug 6;27(15):2171-80. Epub 2008 Jul 17.

    Crystal structures of the OmpF porin: function in a colicin translocon.

    Source

    Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392, USA.

    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.

    PMID:
    18636093
    [PubMed - indexed for MEDLINE]
    PMCID:
    PMC2516885
    Free PMC Article

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