Ghane Tahereh, Gorriz Rene F, Wrzalek Sandro, Volkenandt Senta, Dalatieh Ferand, Reidelbach Marco, Imhof Petra
Institute of Theoretical Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
R Institute GmbH, Dortustraße 48, 14467, Potsdam, Germany.
J Membr Biol. 2018 Jun;251(3):299-314. doi: 10.1007/s00232-018-0019-x. Epub 2018 Feb 12.
Proton transfer in cytochrome c oxidase (CcO) from the cellular inside to the binuclear redox centre as well as proton pumping through the membrane takes place through proton entrance via two distinct pathways, the D- and K-channel. Both channels show a dependence of their hydration level on the protonation states of their key residues, K362 for the K-channel, and E286 or D132 for the D-channel. In the oxidative half of CcO's catalytic cycle the D-channel is the proton-conducting path. For this channel, an interplay of protonation state of the D-channel residues with the water and hydrogen-bond dynamics has been observed in molecular dynamics simulations of the CcO protein, embedded in a lipid bi-layer, modelled in different protonation states. Protonation of residue E286 at the end of the D-channel results in a hydrogen-bonded network pointing from E286 to N139, that is against proton transport, and favouring N139 conformations which correspond to a closed asparagine gate (formed by residues N121 and N139). Consequently, the hydration level is lower than with unprotonated E286. In those models, the Asn gate is predominantly open, allowing water molecules to pass and thus increase the hydration level. The hydrogen-bonded network in these states exhibits longer life times of the Asn residues with water than other models and shows the D-channel to be traversable from the entrance, D132, to exit, E286. The D-channel can thus be regarded as auto-regulated with respect to proton transport, allowing proton passage only when required, that is the proton is located at the lower part of the D-channel (D132 to Asn gate) and not at the exit (E286).
细胞色素c氧化酶（CcO）中质子从细胞内部转移至双核氧化还原中心以及质子跨膜泵送是通过两个不同的途径，即D通道和K通道进行质子内流来实现的。两个通道的水合水平都依赖于其关键残基的质子化状态，K通道的关键残基是K362，D通道的关键残基是E286或D132。在CcO催化循环的氧化阶段，D通道是质子传导路径。对于该通道，在嵌入脂质双分子层并模拟了不同质子化状态的CcO蛋白的分子动力学模拟中，观察到D通道残基的质子化状态与水及氢键动力学之间存在相互作用。D通道末端的残基E286质子化会导致一个从E286指向N139的氢键网络，这不利于质子运输，且有利于与关闭的天冬酰胺门（由残基N121和N139形成）相对应的N139构象。因此，水合水平低于未质子化的E286时的情况。在这些模型中，天冬酰胺门主要是开放的，允许水分子通过，从而提高水合水平。与其他模型相比，这些状态下的氢键网络中天冬酰胺残基与水的结合寿命更长，并且显示D通道从入口D132到出口E286是可穿越的。因此，D通道在质子运输方面可被视为自动调节的，仅在需要时允许质子通过，即质子位于D通道的下部（从D132到天冬酰胺门）而非出口（E286）处时。
