Magalhães Pedro R, Oliveira A Sofia F, Campos Sara R R, Soares Cláudio M, Baptista António M
Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa , 2781-901 Oeiras, Portugal.
J Chem Inf Model. 2017 Feb 27;57(2):256-266. doi: 10.1021/acs.jcim.6b00575. Epub 2017 Jan 31.
Cytochrome c oxidase (CcO) couples the reduction of dioxygen to water with transmembrane proton pumping, which leads to the generation of an electrochemical gradient. In this study we analyze how one of the components of the electrochemical gradient, the difference in pH across the membrane, or ΔpH, influences the protonation states of residues in CcO. We modified our continuum electrostatics/Monte Carlo (CE/MC) method in order to include the ΔpH and applied it to the study of CcO, in what is, to our best knowledge, the first CE/MC study of CcO in the presence of a pH gradient. The inclusion of a transmembrane pH gradient allows for the identification of residues whose titration behavior depends on the pH on both sides of the membrane. Among the several residues with unusual titration profiles, three are well-known key residues in the proton transfer process of CcO: E286, Y288, and K362. All three residues have been previously identified as being critical for the catalytic or proton pumping functions of CcO. Our results suggest that when the pH gradient increases, these residues may be part of a regulatory mechanism to stem the proton flow.
细胞色素c氧化酶（CcO）将氧气还原为水的过程与跨膜质子泵浦相偶联，从而导致电化学梯度的产生。在本研究中，我们分析了电化学梯度的一个组成部分，即跨膜pH差异或ΔpH，如何影响CcO中残基的质子化状态。我们改进了连续介质静电学/蒙特卡罗（CE/MC）方法以纳入ΔpH，并将其应用于CcO的研究，据我们所知，这是首次在存在pH梯度的情况下对CcO进行CE/MC研究。纳入跨膜pH梯度能够识别其滴定行为取决于膜两侧pH的残基。在具有异常滴定曲线的几个残基中，有三个是CcO质子转移过程中众所周知的关键残基：E286、Y288和K362。此前已确定这三个残基对CcO的催化或质子泵浦功能至关重要。我们的结果表明，当pH梯度增加时，这些残基可能是阻止质子流动的调节机制的一部分。
