Department of Chemical and Environmental Sciences, University of Limerick, Limerick, Ireland.
Nature. 2012 Jul 26;487(7408):514-8. doi: 10.1038/nature11182.
Cytochrome c oxidase is a member of the haem copper oxidase superfamily (HCO). HCOs function as the terminal enzymes in the respiratory chain of mitochondria and aerobic prokaryotes, coupling molecular oxygen reduction to transmembrane proton pumping. Integral to the enzyme's function is the transfer of electrons from cytochrome c to the oxidase via a transient association of the two proteins. Electron entry and exit are proposed to occur from the same site on cytochrome c. Here we report the crystal structure of the caa3-type cytochrome oxidase from Thermus thermophilus, which has a covalently tethered cytochrome c domain. Crystals were grown in a bicontinuous mesophase using a synthetic short-chain monoacylglycerol as the hosting lipid. From the electron density map, at 2.36 Å resolution, a novel integral membrane subunit and a native glycoglycerophospholipid embedded in the complex were identified. Contrary to previous electron transfer mechanisms observed for soluble cytochrome c, the structure reveals the architecture of the electron transfer complex for the fused cupredoxin/cytochrome c domain, which implicates different sites on cytochrome c for electron entry and exit. Support for an alternative to the classical proton gate characteristic of this HCO class is presented.
细胞色素 c 氧化酶是血红素铜氧化酶超家族 (HCO) 的成员。HCO 作为线粒体和需氧原核生物呼吸链的末端酶，将分子氧还原与跨膜质子泵耦联。该酶的功能整合到将电子从细胞色素 c 通过两种蛋白质的瞬时缔合转移到氧化酶的过程中。电子的进入和退出据推测发生在细胞色素 c 的相同部位。在这里，我们报告了来自嗜热栖热菌的 caa3 型细胞色素氧化酶的晶体结构，该结构具有共价连接的细胞色素 c 结构域。使用合成的短链单酰基甘油作为宿主脂质在双连续中间相生长晶体。从电子密度图中，在 2.36Å分辨率下，鉴定出一种新型的整合膜亚基和嵌入复合物中的天然糖基甘油磷脂。与先前观察到的可溶性细胞色素 c 的电子转移机制相反，该结构揭示了融合的铜肽酶/细胞色素 c 结构域的电子转移复合物的架构，这表明细胞色素 c 上的不同部位用于电子的进入和退出。提出了对该 HCO 类特征的经典质子门的替代方案。
