Redox-Dependent Conformational Changes in Cytochrome a Oxidase Suggest a Gating Mechanism for Proton Uptake
Redox-Dependent Conformational Changes in Cytochrome a Oxidase Suggest a Gating Mechanism for Proton Uptake
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DOI：
10.1021/bi9001387
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发表时间：
2009-06-16
期刊：
影响因子：
2.9
通讯作者：
Ferguson-Miller, Shelagh
中科院分区：
文献类型：
--
作者：
Qin, Ling;Liu, Jian;Ferguson-Miller, Shelagh
构象变化在细胞色素c氧化酶偶联机制中的作用是一个有争议的问题。在牛氧化酶的还原和氧化晶体结构的比较中，已经报道了相对较小的构象变化，但在细菌氧化酶中没有。比较了还原态的X射线晶体结构，（在2.15埃分辨率下）和来自球形红细菌的细胞色素c氧化酶的氧化形式，我们观察到血红素a（3）的置换，其涉及卟啉环和羟基法尼基尾部，伴随着附近区域的蛋白质移动，包括亚基I的螺旋VIII的中间部分，其具有K质子吸收路径的关键残基，K362和T359。还原形式的构象变化在再氧化时是可逆的。它们导致K路径顶部打开，并在该区域解析更多有序的沃茨，这表明质子有一条进入活性位点的通道。在氧化R的所有高分辨率结构中。在球状体细胞色素c氧化酶中，在D路径顶部上方的疏水区域中观察到水分子，其策略性地定位以促进亚基I的残基E286与活性位点或质子泵出路径的连接。在还原和还原加氰化物结构中，该水分子消失，这意味着在K路径打开的条件下，D路径的质子传导中断，从而提供了一种交替进入活性位点的机制。
A role for conformational change in the coupling mechanism of cytochrome c oxidase is the subject of controversy. Relatively small conformational changes have been reported in comparisons of reduced and oxidized crystal structures of bovine oxidase but none in bacterial oxidases. Comparing the X-ray crystal structures of the reduced (at 2.15 angstrom resolution) and oxidized forms of cytochrome c oxidase from Rhodobacter sphaeroides, we observe a displacement of heme a(3) involving both the porphyrin ring and the hydroxyl farnesyl tail, accompanied by protein movements in nearby regions, including the mid part of helix VIII of subunit I which harbors key residues of the K proton uptake path, K362 and T359. The conformational changes in the reduced form are reversible upon reoxidation. They result in an opening of the top of the K pathway and more ordered waters being resolved in that region, suggesting an access path for protons into the active site. In all high-resolution structures of oxidized R. sphaeroides cytochrome c oxidase, a water molecule is observed in the hydrophobic region above the top of the D path, strategically positioned to facilitate the connection of residue E286 of subunit I to the active site or to the proton pumping exit path. In the reduced and reduced plus cyanide structures, this water molecule disappears, Implying disruption of proton conduction from the D path under conditions when the K path is open, thus providing a mechanism for alternating access to the active site.