Emeline Barbet-Massin, Gregorio Giuseppe de Palma, Barth-Jan van Rossum, Andrew J. Nieuwkoop, W. Trent Franks, Werner Kühlbrandt, Benjamin Bardiaux, Loren B. Andreas, Lyndon Emsley, Victoria A. Higman, Hartmut Oschkinat, Lieselotte Handel, Guido Pintacuda, Jan Stanek, Kutti R. Vinothkumar, J. Retel, Matthias Hiller, Leibniz Forschungsinstitut für Molekulare Pharmakolgie = Leibniz Institute for Molecular Pharmacology [Berlin, Allemagne] (FMP), Leibniz Association, Biological Solid-State NMR Methods - Méthodes de RMN à l'état solide en biologie, Institut des Sciences Analytiques (ISA), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Max-Planck-Institut für Biophysik - Max Planck Institute of Biophysics (MPIBP), Max-Planck-Gesellschaft, Bioinformatique structurale - Structural Bioinformatics, Institut Pasteur [Paris] (IP)-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences et Ingénierie Chimiques (ISIC), Ecole Polytechnique Fédérale de Lausanne (EPFL), This work was supported from a Joint Research Activity in the 7th Framework program of the EC (BioNMR No. 261863), the EU-project iNext (infrastructure for NMR, EM, and X-rays for Translational Research, GA 653706), and the Deutsche Forschungsgemeinschaft (SFB 740 and OS106/9). A.J.N. was supported by fellowships from the Fulbright Program and the Alexander von Humboldt Foundation., European Project, European Project: 653706,H2020,H2020-INFRAIA-2014-2015,iNEXT(2015), Institut de Chimie du CNRS (INC)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS), and Institut Pasteur [Paris]-Centre National de la Recherche Scientifique (CNRS)
β-barrel proteins mediate nutrient uptake in bacteria and serve vital functions in cell signaling and adhesion. For the 14-strand outer membrane protein G of Escherichia coli, opening and closing is pH-dependent. Different roles of the extracellular loops in this process were proposed, and X-ray and solution NMR studies were divergent. Here, we report the structure of outer membrane protein G investigated in bilayers of E. coli lipid extracts by magic-angle-spinning NMR. In total, 1847 inter-residue 1H–1H and 13C–13C distance restraints, 256 torsion angles, but no hydrogen bond restraints are used to calculate the structure. The length of β-strands is found to vary beyond the membrane boundary, with strands 6–8 being the longest and the extracellular loops 3 and 4 well ordered. The site of barrel closure at strands 1 and 14 is more disordered than most remaining strands, with the flexibility decreasing toward loops 3 and 4. Loop 4 presents a well-defined helix., Porins, like OmpG, are embedded in the outer membrane of bacteria and facilitate uptake and secretion of nutrients and ions. Here the authors present a protocol for solid state NMR structure determination of proteins larger than 25 kDa and use it to structurally characterize membrane embedded OmpG.