Thermodynamics of Cation Binding to the Sarcoendoplasmic Reticulum Calcium ATPase Pump and Impacts on Enzyme Function.
Thermodynamics of Cation Binding to the Sarcoendoplasmic Reticulum Calcium ATPase Pump and Impacts on Enzyme Function.
复制标题
阳离子与肌内质网钙 ATP 酶泵结合的热力学及其对酶功能的影响。
DOI：
10.1021/acs.jctc.8b01312
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发表时间：
2019
影响因子：
5.5
通讯作者：
Kekenes-Huskey,PeterM
中科院分区：
文献类型：
--
作者：
Sun,Bin;Stewart,BradleyD;Kucharski,AmirN;Kekenes-Huskey,PeterM
肌内质网Ca ~（2+）-ATP酶（SERCA）是一种跨膜泵，在肌浆网钙转运中起重要作用。虽然钙（Ca 2+）以微摩尔亲和力结合SERCA，但镁（Mg 2+）和钾（K+）也与Ca 2+结合竞争。然而，这些竞争离子对SERCA功能和泵对Ca 2+的选择性的影响的分子基础还没有很好地建立。因此，我们使用计算机模拟方法来解析在典型位点I和II Ca 2+结合位点中阳离子结合的分子决定簇，通过（1）Mg 2+、Ca 2+和K+结合的SERCA的一式三份分子动力学（MD）模拟，（2）平均球近似（MSA）理论来对阳离子结合到MD解析结构的亲和力和选择性进行评分，和（3）状态模型的SERCA营业额通知从MSA衍生的亲和力数据。我们的主要发现是（a）位点I和II的配位对于Ca 2+是最优化的，并且对于Mg 2+和K+在较小程度上是最优化的，如通过MD衍生的阳离子-氨基酸氧和结合水构型所确定的，（B）Mg 2+的受损配位和高去溶剂化成本排除了相对于Ca 2+的有利的Mg 2+结合，而K+结合位点I的能力有限，（c）基于SERCA周转的最佳拟合状态模型，Mg ~（2+）在SERCA的反应循环中最有可能起抑制剂的作用，而K ~+则最有可能起中间体的作用。这些发现为SERCA功能提供了定量基础，该功能利用了分子尺度的热力学数据，并在广泛的K+，Ca 2+和Mg 2+浓度范围内合理化酶活性。
Sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) is a transmembrane pump that plays an important role in transporting calcium into the sarcoplasmic reticulum (SR). While calcium (Ca2+) binds SERCA with micromolar affinity, magnesium (Mg2+) and potassium (K+) also compete with Ca2+binding. However, the molecular bases for these competing ions’ influence on the SERCA function and the selectivity of the pump for Ca2+are not well-established. We therefore used in silico methods to resolve molecular determinants of cation binding in the canonical site I and II Ca2+binding sites via (1) triplicate molecular dynamics (MD) simulations of Mg2+, Ca2+, and K+-bound SERCA, (2) mean spherical approximation (MSA) theory to score the affinity and selectivity of cation binding to the MD-resolved structures, and (3) state models of SERCA turnover informed from MSA-derived affinity data. Our key findings are that (a) coordination at sites I and II is optimized for Ca2+and to a lesser extent for Mg2+and K+, as determined by MD-derived cation–amino acid oxygen and bound water configurations, (b) the impaired coordination and high desolvation cost for Mg2+precludes favorable Mg2+binding relative to Ca2+, while K+has limited capacity to bind site I, and (c) Mg2+most likely acts as inhibitor and K+as intermediate in SERCA’s reaction cycle, based on a best-fit state model of SERCA turnover. These findings provide a quantitative basis for SERCA function that leverages molecular-scale thermodynamic data and rationalizes enzyme activity across broad ranges of K+, Ca2+, and Mg2+concentrations.