Electrostatic attraction of weak monoacid anions increases probability for protonation and passage through aquaporins
Electrostatic attraction of weak monoacid anions increases probability for protonation and passage through aquaporins
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DOI：
10.1074/jbc.m117.782516
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发表时间：
2017-06-02
影响因子：
4.8
通讯作者：
Beitz, Eric
中科院分区：
文献类型：
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作者：
Rothert, Monja;Roenfeldt, Deike;Beitz, Eric
从水通道蛋白（AQP）的水和溶质通道的中心发出的正静电场负责阳离子的排斥。然而，与此同时，正电场会吸引负离子。在这方面，L-乳酸盐/乳酸渗透性已被证明是其他高度水和中性底物选择性AQP家族的各种亚型。使某些水通道蛋白对弱一元酸具有渗透性的结构要求和传导机制仍不清楚。在这里，我们通过分析pH依赖性底物渗透性，测量介质碱化和质子去耦，表明AQP 9作为质子化的中性单羧酸物质的通道。有趣的是，所获得的渗透率表明高达10倍以上的概率通过AQP 9比给定的质子化酸底物的分数在一定的pH值。我们产生的AQP 9点突变体显示，这种效果是独立的通道内部的属性，但引起的蛋白质表面静电。因此，一元羧酸传导性水通道蛋白采用类似于弱一元酸的甲酸盐-亚硝酸盐转运蛋白家族的机制。在一个更一般的基础上，我们的数据说明半定量的贡献，表面静电带电分子基板或配体与靶蛋白，如通道，转运蛋白，酶，或受体的相互作用。
A positive electrostatic field emanating from the center of the aquaporin (AQP) water and solute channel is responsible for the repulsion of cations. At the same time, however, a positive field will attract anions. In this regard, L-lactate/lactic acid permeability has been shown for various isoforms of the otherwise highly water and neutral substrate selective AQP family. The structural requirements rendering certain AQPs permeable for weak monoacids and the mechanism of conduction have remained unclear. Here, we show by profiling pH-dependent substrate permeability, measurements of media alkalization, and proton decoupling that AQP9 acts as a channel for the protonated, neutral monocarboxylic acid species. Intriguingly, the obtained permeability rates indicate an up to 10 times higher probability of passage via AQP9 than given by the fraction of the protonated acid substrate at a certain pH. We generated AQP9 point mutants showing that this effect is independent from properties of the channel interior but caused by the protein surface electrostatics. Monocarboxylic acid-conducting AQPs thus employ a mechanism similar to the family of formate-nitrite transporters for weak monoacids. On a more general basis, our data illustrate semiquantitatively the contribution of surface electrostatics to the interaction of charged molecule substrates or ligands with target proteins, such as channels, transporters, enzymes, or receptors.