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Identification of a cation transport pathway in Neisseria meningitidis PorB

Authors

  • Christof Kattner,

    1. HALOmem, Institut für Biochemie und Biotechnologie, Martin-Luther-Universität Halle-Wittenberg, Halle (Saale), Germany
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    • These authors have contributed equally to this work.

  • Jan Zaucha,

    1. SUPA, School of Physics and Astronomy, The University of Edinburgh, Edinburgh, United Kingdom
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    • These authors have contributed equally to this work.

  • Frank Jaenecke,

    1. HALOmem, Institut für Biochemie und Biotechnologie, Martin-Luther-Universität Halle-Wittenberg, Halle (Saale), Germany
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  • Ulrich Zachariae,

    Corresponding author
    1. SUPA, School of Physics and Astronomy, The University of Edinburgh, Edinburgh, United Kingdom
    • SUPA, School of Physics and Astronomy, The King's Buildings, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom. E-mail: uzachari@ph.ed.ac.uk or Mikio Tanabe; HALOmem, Membrane Protein Biochemistry, Institut für Biochemie und Biotechnologie, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Str.3 D-06120 Halle (Saale), Germany
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  • Mikio Tanabe

    Corresponding author
    1. HALOmem, Institut für Biochemie und Biotechnologie, Martin-Luther-Universität Halle-Wittenberg, Halle (Saale), Germany
    • SUPA, School of Physics and Astronomy, The King's Buildings, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom. E-mail: uzachari@ph.ed.ac.uk or Mikio Tanabe; HALOmem, Membrane Protein Biochemistry, Institut für Biochemie und Biotechnologie, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Str.3 D-06120 Halle (Saale), Germany
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Abstract

Neisseria meningitidis is the main causative agent of bacterial meningitis. In its outer membrane, the trimeric Neisserial porin PorB is responsible for the diffusive transport of essential hydrophilic solutes across the bilayer. Previous molecular dynamics simulations based on the recent crystal structure of PorB have suggested the presence of distinct solute translocation pathways through this channel. Although PorB has been electrophysiologically characterized as anion-selective, cation translocation through nucleotide-bound PorB during pathogenesis is thought to be instrumental for host cell death. As a result, we were particularly interested in further characterizing cation transport through the pore. We combined a structural approach with additional computational analysis. Here, we present two crystal structures of PorB at 2.1 and 2.65 Å resolution. The new structures display additional electron densities around the protruding loop 3 (L3) inside the pore. We show that these electron densities can be identified as monovalent cations, in our case Cs+, which are tightly bound to the inner channel. Molecular dynamics simulations reveal further ion interactions and the free energy landscape for ions inside PorB. Our results suggest that the crystallographically identified locations of Cs+ form a cation transport pathway inside the pore. This finding suggests how positively charged ions are translocated through PorB when the channel is inserted into mitochondrial membranes during Neisserial infection, a process which is considered to dissipate the mitochondrial transmembrane potential gradient and thereby induce apoptosis. Proteins 2013. © 2012 Wiley Periodicals, Inc.

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