Article
- The EMBO Journal (2008) 27, 2171 - 2180
- doi:10.1038/emboj.2008.137
Published online: 17 July 2008
Subject Categories:
Crystal structures of the OmpF porin: function in a colicin translocon
Eiki Yamashita1,a, Mariya V Zhalnina1, Stanislav D Zakharov1,2, Onkar Sharma1 and William A Cramer1
- Department of Biological Sciences, Purdue University, West Lafayette, IN, USA
- Institute of Basic Problems of Biology, Russian Academy of Sciences, Puschino, Moscow Region, Russian Federation
Correspondence to:
William A Cramer, Department of Biological Sciences, Purdue University, Lilly Hall of Life Sciences, West Lafayette, Indiana 47907-1392, USA. Tel.: +1 765 494 4956; Fax: +1 765 496 1189; E-mail: waclab@purdue.edu
aPresent address: Institute for Protein Research, Osaka University, Osaka, Japan
Received 15 April 2008; Accepted 24 June 2008
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 Å 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 Å 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.
Keywords:
- colicin E3,
- intrinsically disordered protein,
- OmpF porin,
- receptor BtuB,
- tol system
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