Hess Berk, van der Vegt Nico F A
Max-Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.
Proc Natl Acad Sci U S A. 2009 Aug 11;106(32):13296-300. doi: 10.1073/pnas.0902904106. Epub 2009 Jul 28.
Biological organization depends on a sensitive balance of noncovalent interactions, in particular also those involving interactions between ions. Ion-pairing is qualitatively described by the law of "matching water affinities." This law predicts that cations and anions (with equal valence) form stable contact ion pairs if their sizes match. We show that this simple physical model fails to describe the interaction of cations with (molecular) anions of weak carboxylic acids, which are present on the surfaces of many intra- and extracellular proteins. We performed molecular simulations with quantitatively accurate models and observed that the order K(+) < Na(+) < Li(+) of increasing binding affinity with carboxylate ions is caused by a stronger preference for forming weak solvent-shared ion pairs. The relative insignificance of contact pair interactions with protein surfaces indicates that thermodynamic stability and interactions between proteins in alkali salt solutions is governed by interactions mediated through hydration water molecules.
生物组织依赖于非共价相互作用的敏感平衡，特别是那些涉及离子间相互作用的平衡。离子配对在定性上由“匹配水亲和力”定律描述。该定律预测，阳离子和阴离子（价态相等）如果大小匹配，就会形成稳定的接触离子对。我们表明，这个简单的物理模型无法描述阳离子与许多细胞内和细胞外蛋白质表面存在的弱羧酸（分子）阴离子的相互作用。我们用定量精确的模型进行了分子模拟，观察到与羧酸根离子结合亲和力增加的顺序为K(+) < Na(+) < Li(+)，这是由于形成弱溶剂共享离子对的更强偏好所致。与蛋白质表面接触对相互作用的相对不重要表明，碱金属盐溶液中蛋白质之间的热力学稳定性和相互作用是由通过水化水分子介导的相互作用所控制的。
