Keeping it simple, transport mechanism and pH regulation in Na+/H+ exchangers.
Keeping it simple, transport mechanism and pH regulation in Na+/H+ exchangers.
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DOI：
10.1074/jbc.m113.542993
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发表时间：
2014-05-09
期刊：
影响因子：
--
通讯作者：
Fendler K
中科院分区：
文献类型：
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作者：
Călinescu O;Paulino C;Kühlbrandt W;Fendler K
背景：Na+/H+ 交换剂具有明显的 pH 依赖性，之前已通过 pH 传感器进行了解释。结果：对来自詹氏甲烷球菌 (MjNhaP1) 的 NhaP1（电中性 Na+/H+ 交换器原型）的电生理学研究，使其动力学特征得以表征。结论：Na+/H+ 交换剂的 pH 依赖性是其传输机制的固有特性。意义：所提出的运输和 pH 调节机制适用于所有 Na+/H+ 交换剂。 Na+/H+ 交换器对于调节所有生物体的细胞内质子和钠浓度至关重要。我们检查并通过实验验证了 Na+/H+ 交换剂的动力学模型，其中单个结合位点交替被 Na+ 或一个或两个 H+ 离子占据。所提出的转运机制本质上在极端 pH 值下下调 Na+/H+ 交换剂，防止细胞质过度酸化或碱化。作为一个实验测试系统，我们首次对电中性 Na+/H+ 交换器 NhaP1 进行了电生理学研究，该交换器来自詹氏甲烷球菌 (MjNhaP1)，它是医学上重要的真核 NHE Na+/H+ 交换器的密切同源物。动力学模型描述了实验观察到的 MjNhaP1 底物依赖性，传输机制解释了 MjNhaP1 的碱性下调。由于该模型还解释了大肠杆菌的产电 NhaA Na+/H+ 交换剂（EcNhaA，在之前的出版物中显示）的酸性下调，因此我们得出结论，它通常适用于所有 Na+/H+ 交换剂，无论是产电的还是电中性的，并优雅地解释了它们的 pH 调节。此外，电生理学分析可以深入了解电中性和产电 Na+/H+ 交换器中易位复合物的静电结构。
Background: Na+/H+ exchangers have a pronounced pH dependence previously explained by pH sensors. Results: Electrophysiological investigation of NhaP1 from Methanocaldococcus jannaschii (MjNhaP1), a prototype of electroneutral Na+/H+ exchangers, allowed its kinetic characterization. Conclusion: The pH dependence of Na+/H+ exchangers is an inherent property of their transport mechanism. Significance: The proposed mechanism of transport and pH regulation applies to all Na+/H+ exchangers. Na+/H+ exchangers are essential for regulation of intracellular proton and sodium concentrations in all living organisms. We examined and experimentally verified a kinetic model for Na+/H+ exchangers, where a single binding site is alternatively occupied by Na+ or one or two H+ ions. The proposed transport mechanism inherently down-regulates Na+/H+ exchangers at extreme pH, preventing excessive cytoplasmic acidification or alkalinization. As an experimental test system we present the first electrophysiological investigation of an electroneutral Na+/H+ exchanger, NhaP1 from Methanocaldococcus jannaschii (MjNhaP1), a close homologue of the medically important eukaryotic NHE Na+/H+ exchangers. The kinetic model describes the experimentally observed substrate dependences of MjNhaP1, and the transport mechanism explains alkaline down-regulation of MjNhaP1. Because this model also accounts for acidic down-regulation of the electrogenic NhaA Na+/H+ exchanger from Escherichia coli (EcNhaA, shown in a previous publication) we conclude that it applies generally to all Na+/H+ exchangers, electrogenic as well as electroneutral, and elegantly explains their pH regulation. Furthermore, the electrophysiological analysis allows insight into the electrostatic structure of the translocation complex in electroneutral and electrogenic Na+/H+ exchangers.