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Crystal structures of the OmpF porin: function in a colicin translocon
Author(s) -
Yamashita Eiki,
Zhalnina Mariya V,
Zakharov Stanislav D,
Sharma Onkar,
Cramer William A
Publication year - 2008
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1038/emboj.2008.137
Subject(s) - colicin , porin , bacterial outer membrane , biology , translocon , escherichia coli , crystallography , biophysics , peptide sequence , biochemistry , membrane , membrane protein , chemistry , gene
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 Å OmpF structure, obtained from crystals formed in 1 M Mg 2+ , has one Mg 2+ 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 Å structure with inserted T83, which was obtained without Mg 2+ 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 Mg 2+ binding site obtained without T83, explaining the absence of peptide binding in the presence of Mg 2+ . 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.