A model for coupling of H(+) and substrate fluxes based on "time-sharing" of a common binding site.
A model for coupling of H(+) and substrate fluxes based on "time-sharing" of a common binding site.
复制标题
基于公共结合位点“分时”的 H( ) 和底物通量耦合模型。
DOI：
10.1021/bi001892i
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发表时间：
2000
期刊：
影响因子：
2.9
通讯作者：
Schuldiner,S
中科院分区：
文献类型：
--
作者：
Yerushalmi,H;Schuldiner,S
原核细胞和真核细胞都含有一系列维持细胞稳态的膜运输系统。其中一些（主泵）从氧化还原反应、ATP 水解或光吸收中获取能量，而另一些（离子耦合转运蛋白）则利用离子电化学梯度进行主动转运。在理解其中一些系统中耦合的分子机制方面已经取得了显着的进展。在许多情况下，羧基残基对于结合或偶联是必需的。在这里，我们提出了 EmrE（一种大肠杆菌 12-kDa 多药物转运蛋白）耦合分子机制的模型。 EmrE 通过将多种有毒阳离子从细胞内部去除以换取两个质子来赋予其抵抗力。 EmrE 只有一个膜嵌入的带电残基 Glu-14，它在 50 多种同源蛋白中是保守的。我们使用诱变和化学修饰来证明 Glu-14 是底物结合位点的一部分。通过研究 pH 对配体结合、摄取、流出和交换反应的影响，证明了它在质子结合和易位中的作用。研究表明，Glu-14 是底物和质子共有的结合位点的重要组成部分。 H+ 和底物对该位点的占据是互斥的，并为两种通量提供了最简单的耦合的基础。
Both prokaryotic and eukaryotic cells contain an array of membrane transport systems maintaining the cellular homeostasis. Some of them (primary pumps) derive energy from redox reactions, ATP hydrolysis, or light absorption, whereas others (ion-coupled transporters) utilize ion electrochemical gradients for active transport. Remarkable progress has been made in understanding the molecular mechanism of coupling in some of these systems. In many cases carboxylic residues are essential for either binding or coupling. Here we suggest a model for the molecular mechanism of coupling in EmrE, anEscherichia coli12-kDa multidrug transporter. EmrE confers resistance to a variety of toxic cations by removing them from the cell interior in exchange for two protons. EmrE has only one membrane-embedded charged residue, Glu-14, which is conserved in more than 50 homologous proteins. We have used mutagenesis and chemical modification to show that Glu-14 is part of the substrate-binding site. Its role in proton binding and translocation was shown by a study of the effect of pH on ligand binding, uptake, efflux, and exchange reactions. The studies suggest that Glu-14 is an essential part of a binding site, which is common to substrates and protons. The occupancy of this site by H+and substrate is mutually exclusive and provides the basis of the simplest coupling for two fluxes.