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The molecular basis of phosphate discrimination in arsenate-rich environments

机译：富含砷酸盐的环境中磷酸盐鉴别的分子基础

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摘要

Arsenate and phosphate are abundant on Earth and have striking similarities: nearly identical pK_a values, similarly charged oxygen atoms, and thermochemical radii that differ by only 4% (ref. 3). Phosphate is indispensable and arsenate is toxic, but this extensive similarity raises the question whether arsenate may substitute for phosphate in certain niches. However, whether it is used or excluded, discriminating phosphate from arsenate is a paramount challenge. Enzymes that utilize phosphate, for example, have the same binding mode and kinetic parameters as arsenate, and the latter's presence therefore, decouples metabolism. Can proteins discriminate between these two anions, and how would they do so? In particular, cellular phosphate uptake systems face a challenge in arsenate-rich environments. Here we describe a molecular mechanism for this process. We examined the periplasmic phosphate-binding proteins (PBPs) of the ABC-type transport system that mediates phosphate uptake into bacterial cells, including two PBPs from the arsenate-rich Mono Lake Halomonas strain GFAJ-1. All PBPs tested are capable of discriminating phosphate over arsenate at least 500-fold. The exception is one of the PBPs of GFAJ-1 that shows roughly 4,500-fold discrimination and its gene is highly expressed under phosphate-limiting conditions. Sub-angstrom-resolution structures of Pseudomonas Quorescens PBP with both arsenate and phosphate show a unique mode of binding that mediates discrimination. An extensive network of dipole-anion interactions, and of repulsive interactions, results in the 4% larger arsenate distorting a unique low-barrier hydrogen bond. These features enable the phosphate transport system to bind phosphate selectively over arsenate (at least 10~3 excess) even in highly arsenate-rich environments.
机译：砷和磷酸盐在地球上非常丰富，并且具有惊人的相似之处：几乎相同的pK_a值，带相似电荷的氧原子和热化学半径的差别仅为4％（参考文献3）。磷酸盐是必不可少的，砷酸盐是有毒的，但是这种广泛的相似性引发了一个问题，砷酸盐是否可以在某些壁ni中替代磷酸盐。但是，无论使用还是排除，将砷酸根与磷酸盐区分开来都是一项首要挑战。例如，利用磷酸盐的酶具有与砷酸盐相同的结合模式和动力学参数，因此后者的存在使新陈代谢解耦。蛋白质可以区分这两种阴离子吗？它们将如何区分？特别是，细胞磷酸盐吸收系统在富含砷酸盐的环境中面临挑战。在这里，我们描述了此过程的分子机制。我们检查了介导磷酸盐吸收到细菌细胞中的ABC型运输系统的周质磷酸盐结合蛋白（PBP），包括富含砷酸盐的Mono Lake Halomonas菌株GFAJ-1的两个PBP。所有测试的PBP都能区分砷酸盐至少500倍的磷酸盐。 GFAJ-1的PBP之一是例外，它显示出大约4,500倍的区分力，并且其基因在磷酸盐限制条件下高度表达。亚砷酸根结构的假单胞菌PBP具有砷酸盐和磷酸盐的结合结构表现出独特的结合模式，可介导歧视。偶极-阴离子相互作用和排斥相互作用的广泛网络导致砷酸盐大4％，扭曲了独特的低势垒氢键。这些特征使磷酸盐转运系统即使在富含砷酸盐的环境中也能选择性地与磷酸盐（至少10〜3过量）结合磷酸盐。

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  • 来源
    《Nature》 |2012年第7422期|p.134-137|共4页
  • 作者

    Mikael Elias; Alon Wellner; Korina Goldin-Azulay; Eric Chabriere; Julia A. Vorholt; Tobias J. Erb; Dan S. Tawfik;

  • 作者单位

    Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel;

    Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel;

    Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel;

    Unite de recherche sur les maladies infectieuses et tropicales emergentes, Faculte de Medecine et de Pharmacie, CNRS-Universite de la Mediterranee, 13385 Marseille, France;

    Institute of Microbiology, Eidgenoessische Technische Hochschule Zurich, Wolfgang Pauli Strasse 10,8093 Zurich, Switzerland;

    Institute of Microbiology, Eidgenoessische Technische Hochschule Zurich, Wolfgang Pauli Strasse 10,8093 Zurich, Switzerland;

    Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel;

  • 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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