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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Selectivity of externally facing ion-binding sites in the Na/K pump to alkali metals and organic cations
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Selectivity of externally facing ion-binding sites in the Na/K pump to alkali metals and organic cations

机译：Na / K泵中面向外部的离子结合位点对碱金属和有机阳离子的选择性

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摘要

The Na/K pump is a P-type ATPase that exchanges three intracel-lular Na~+ ions for two extracellular K~+ ions through the plasma-lemma of nearly all animal cells. The mechanisms involved in cation selection by the pump's ion-binding sites (site Ⅰ and site Ⅱ bind either Na~+ or K~+; site Ⅲ binds only Na~+) are poorly understood. We studied cation selectivity by outward-facing sites (high K~+ affinity) of Na/K pumps expressed in Xenopus oocytes, under voltage clamp. Guanidinium~+, methylguanidinium~+, and aminoguanidi-nium~+ produced two phenomena possibly reflecting actions at site Ⅲ: (ⅰ) voltage-dependent inhibition (VDI) of outwardly directed pump current at saturating K~+, and (ⅱ) induction of pump-mediated, guanidinium-derivative-carried inward current at negative potentials without Na~+ and K~+. In contrast, formamidinium~+ and acetamidinium~+ induced K~+-like outward currents. Measurement of ouabain-sensitive ATPase activity and radiolabeled cation uptake confirmed that these cations are external K~+ congeners. Molecular dynamics simulations indicate that bound organic cations induce minor distortion of the binding sites. Among tested metals, only Li~+ induced Na~+-like VDI, whereas ail metals tested except Na~+ induced K~+-like outward currents. Pump-mediated K~+-like organic cation transport challenges the concept of rigid structural models in which ion specificity at site Ⅰ and site Ⅱ arises from a precise and unique arrangement of coordinating ligands. Furthermore, actions by guanidinium~+ derivatives suggest that Na~+ binds to site Ⅲ in a hydrated form and that the inward current observed without external Na~+ and K~+ represents cation transport when normal occlusion at sites Ⅰ and Ⅱ is impaired. These results provide insights on external ion selectivity at the three binding sites.
机译：Na / K泵是一种P型ATPase，它通过几乎所有动物细胞的血浆-内膜交换三个细胞内的Na〜+离子为两个胞外的K〜+离子。泵的离子结合位点（位点Ⅰ和位点Ⅱ与Na〜+或K〜+结合；位点Ⅲ仅与Na〜+结合）参与阳离子选择的机理尚不清楚。我们通过在电压钳下在爪蟾卵母细胞中表达的Na / K泵的向外部位（高K〜+亲和力）研究了阳离子选择性。胍盐〜+，甲基胍盐〜+和氨基胍盐〜+在位置Ⅲ处产生了两种可能反映作用的现象：（ⅰ）饱和K〜+时外向泵浦电流的电压依赖性抑制（VDI）和（ⅱ）感应Na +和K +的负电势下泵介导的胍衍生物导引的内向电流的变化。相比之下，甲ami〜+和乙induced〜+会感应出类似K〜+的外向电流。哇巴因敏感性ATPase活性和放射性标记的阳离子摄取的测量结果证实这些阳离子是外部K〜+同系物。分子动力学模拟表明，结合的有机阳离子引起结合位点的轻微变形。在测试的金属中，只有Li〜+诱导了类似Na〜+的VDI，而测试的所有金属除了Na〜+都诱导了K〜+样的外向电流。泵介导的K〜+样有机阳离子迁移对刚性结构模型的概念提出了挑战，在刚性结构模型中，Ⅰ位和Ⅱ位的离子特异性源自配位体的精确而独特的排列。此外，胍基+衍生物的作用表明，Na + +以水合形式结合到Ⅲ位，并且当Ⅰ和Ⅱ位的正常吸附被削弱时，没有外部Na +和K +观察到的内向电流代表阳离子迁移。这些结果提供了对三个结合位点外部离子选择性的见解。

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  • 作者

    lan M. Ratheal; Gail K. Virgin; Haibo Yu; Benott Roux; Craig Gatto; Pablo Artigas;

  • 作者单位

    Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX 79430;

    rnDepartment of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX 79430 School of Biological Sciences, Illinois State University, Normal, IL 61790;

    rnDepartment of Biochemistry and Molecular Biology, University of Chicago, Chicago IL 60637;

    rnDepartment of Biochemistry and Molecular Biology, University of Chicago, Chicago IL 60637;

    rnSchool of Biological Sciences, Illinois State University, Normal, IL 61790;

    rnDepartment of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX 79430;

  • 收录信息 美国《科学引文索引》(SCI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    ion selectivity; Na,K-ATPase; pump current; voltage-dependent; guanidinium;

    机译：离子选择性Na;K-ATPase;泵浦电流电压依赖性胍盐;

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