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Crystal structure of a nitrateitrite exchanger

机译：硝酸盐/亚硝酸盐交换剂的晶体结构

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摘要

Mineral nitrogen in nature is often found in the form of nitrate (NO~-_3). Numerous microorganisms evolved to assimilate nitrate and use it as a major source of mineral nitrogen uptake. Nitrate, which is central in nitrogen metabolism, is first reduced to nitrite (NO~-_2) through a two-electron reduction reaction. The accumulation of cellular nitrite can be harmful because nitrite can be reduced to the cytotoxic nitric oxide. Instead, nitrite is rapidly removed from the cell by channels and transporters, or reduced to ammonium or dinitrogen through the action of assimilatory enzymes. Despite decades of effort no structure is currently available for any nitrate transport protein and the mechanism by which nitrate is transported remains largely unknown. Here we report the structure of a bacterial nitrateitrite transport protein, NarK, from Escherichia coll, with and without substrate. The structures reveal a positively charged substrate-translocation pathway lacking protonatable residues, suggesting that NarK functions as a nitrateitrite exchanger and that protons are unlikely to be co-transported. Conserved arginine residues comprise the substrate-binding pocket, which is formed by association of helices from the two halves of NarK. Key residues that are important for substrate recognition and transport are identified and related to extensive mutagenesis and functional studies. We propose that NarK exchanges nitrate for nitrite by a rocker switch mechanism facilitated by inter-domain hydrogen bond networks.
机译：自然界中的矿物质氮通常以硝酸盐的形式存在（NO〜-_3）。许多微生物进化为吸收硝酸盐，并将其用作吸收矿物质氮的主要来源。在氮代谢中至关重要的硝酸盐首先通过两电子还原反应还原为亚硝酸盐（NO〜-_2）。细胞亚硝酸盐的积累可能是有害的，因为亚硝酸盐可以还原为具有细胞毒性的一氧化氮。取而代之的是，亚硝酸盐通过通道和转运蛋白迅速从细胞中去除，或通过同化酶的作用还原为铵或二氮。尽管付出了数十年的努力，但目前尚无用于任何硝酸盐转运蛋白的结构，而且转运硝酸盐的机理仍然未知。在这里，我们报告了一种细菌硝酸盐/亚硝酸盐转运蛋白NarK的结构，该蛋白来自大肠埃希氏菌，带有和不带有底物。该结构揭示了带正电的底物易位途径，缺少质子化残基，表明NarK充当硝酸盐/亚硝酸盐交换剂，质子不太可能被共同运输。保守的精氨酸残基包含底物结合口袋，其由来自NarK的两半的螺旋的缔合形成。确定了对于底物识别和运输重要的关键残基，并与广泛的诱变和功能研究相关。我们建议通过域间氢键网络促进的跷板开关机制，NarK将硝酸盐交换为亚硝酸盐。

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  • 来源
    《Nature》 |2013年第7451期|647-651|共5页
  • 作者

    Hongjin Zheng; Goragot Wisedchaisri; Tamir Gonen;

  • 作者单位

    Janelia Farm Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, Virginia 20147, USA;

    Janelia Farm Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, Virginia 20147, USA;

    ,Janelia Farm Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, Virginia 20147, USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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