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Insights on Na+ binding and conformational dynamics in multidrug and toxic compound extrusion transporter NorM

Authors

  • Jianing Song,

    1. State Key Laboratory of Precision Spectroscopy, Department of Physics, Institute of Theoretical and Computational Science, East China Normal University, Shanghai, China
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  • Changge Ji,

    Corresponding author
    1. State Key Laboratory of Precision Spectroscopy, Department of Physics, Institute of Theoretical and Computational Science, East China Normal University, Shanghai, China
    2. Institutes for Advanced Interdisciplinary Research, East China Normal University, Shanghai, China
    • Correspondence to: John Z. H. Zhang, Department of Chemistry, New York University, NY 10003. E-mail: john.zhang@nyu.edu or Changge Ji, Institutes for Advanced Interdisciplinary Research, East China Normal University, Shanghai 200062, China. E-mail: chicago.ji@gmail.com

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  • John Z. H. Zhang

    Corresponding author
    1. State Key Laboratory of Precision Spectroscopy, Department of Physics, Institute of Theoretical and Computational Science, East China Normal University, Shanghai, China
    2. Department of Chemistry, New York University, New York
    • Correspondence to: John Z. H. Zhang, Department of Chemistry, New York University, NY 10003. E-mail: john.zhang@nyu.edu or Changge Ji, Institutes for Advanced Interdisciplinary Research, East China Normal University, Shanghai 200062, China. E-mail: chicago.ji@gmail.com

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ABSTRACT

MATE (multidrug and toxic compound extrusion) transporter proteins mediate metabolite transport in plants and multidrug resistance in bacteria and mammals. MATE transporter NorM from Vibrio cholerae is an antiporter that is driven by Na+ gradient to extrude the substrates. To understand the molecular mechanism of Na+-substrate exchange, molecular dynamics simulation was performed to study conformational changes of both wild-type and mutant NorM with and without cation bindings. Our results show that NorM is able to bind two Na+ ions simultaneously, one to each of the carboxylic groups of E255 and D371 in the binding pocket. Furthermore, this di-Na+ binding state is likely more efficient for conformational changes of NorM_VC toward the inward-facing conformation than single-Na+ binding state. The observation of two Na+ binding sites of NorM_VC is consistent with the previous study that two sites for ion binding (denoted as Na1/Na2 sites) are found in the transporter LeuT and BetP, another two secondary transporters. Taken together, our findings shed light on the structure rearrangements of NorM on Na+ binding and enrich our knowledge of the transport mechanism of secondary transporters. Proteins 2014; 82:240–249. © 2013 Wiley Periodicals, Inc.

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