MOMP from Campylobacter jejuni is a trimer of 18-stranded β–barrel monomers with a Ca2+ ion bound at the constriction zone
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The Gram-negative organism Campylobacter jejuni is the major cause of food poisoning. Unlike Escherichia coli which has two major porins, OmpC and OmpF, C. jejuni has one, termed major outer membrane protein (MOMP) through which nutrients and antibiotics transit. We report the 2.1-Å crystal structure of C. jejuni MOMP expressed in E. coli and a lower resolution but otherwise identical structure purified directly from C. jejuni. The 2.1-Å resolution structure of recombinant MOMP showed that although the protein has timeric arrangement similar to OmpC, it is an18-stranded not 16-stranded β-barrel. The structure has identified a Ca2+ bound at the constriction zone, which molecular dynamics and single channel experiments suggest is functionally significant. The water filled channel of MOMP has a narrow constriction zone and single molecule studies show a monomeric conductivity of 0.7 ± 0.2 nS and a trimeric conductance of 2.2 ± 0.2 nS. The ion neutralizes negative charges at the constriction zone reducing the transverse electric field and reversing ion selectivity. Modelling of the transit of ciprofloxacin, an antibiotic of choice for treating Campylobacter infection, through the pore of MOMP reveals a trajectory that is dependent upon the presence metal ion.
Ferrara , L , Wallat , G D , Moynie , L , Dhanasekar , N , Aliouane , S , Acosta-Gutiérrez , S , Pagès , J-M , Bolla , J-M , Winterhalter , M , Ceccarelli , M & Naismith , J H 2016 , ' MOMP from Campylobacter jejuni is a trimer of 18-stranded β–barrel monomers with a Ca 2+ ion bound at the constriction zone ' Journal of Molecular Biology , vol 428 , no. 22 , pp. 4528-4543 . DOI: 10.1016/j.jmb.2016.09.021
Journal of Molecular Biology
© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
LGMF and SG are funded by EU FP7-PEOPLE-2013-ITN Translocation network Nr. 607694. The research leading to these results was conducted as part of the Translocation consortium (www.translocation.com) and has received support from the Innovative Medicines Initiatives Joint Undertaking under Grant Agreement n°115525, resources which are composed of financial contribution from the European Union’s seventh framework programme (FP7/2007-2013) and EFPIA companies in kind contribution. JHN is Royal Society Wolfson Merit Award holder, Senior Investigator Wellcome Trust (WT100209MA) and Chinese Academy of Science 1000 Talent Scholar.
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