Sousa Joana S, D'Imprima Edoardo, Vonck Janet
Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
Subcell Biochem. 2018;87:167-227. doi: 10.1007/978-981-10-7757-9_7.
Mitochondria are the power stations of the eukaryotic cell, using the energy released by the oxidation of glucose and other sugars to produce ATP. Electrons are transferred from NADH, produced in the citric acid cycle in the mitochondrial matrix, to oxygen by a series of large protein complexes in the inner mitochondrial membrane, which create a transmembrane electrochemical gradient by pumping protons across the membrane. The flow of protons back into the matrix via a proton channel in the ATP synthase leads to conformational changes in the nucleotide binding pockets and the formation of ATP. The three proton pumping complexes of the electron transfer chain are NADH-ubiquinone oxidoreductase or complex I, ubiquinone-cytochrome c oxidoreductase or complex III, and cytochrome c oxidase or complex IV. Succinate dehydrogenase or complex II does not pump protons, but contributes reduced ubiquinone. The structures of complex II, III and IV were determined by x-ray crystallography several decades ago, but complex I and ATP synthase have only recently started to reveal their secrets by advances in x-ray crystallography and cryo-electron microscopy. The complexes I, III and IV occur to a certain extent as supercomplexes in the membrane, the so-called respirasomes. Several hypotheses exist about their function. Recent cryo-electron microscopy structures show the architecture of the respirasome with near-atomic detail. ATP synthase occurs as dimers in the inner mitochondrial membrane, which by their curvature are responsible for the folding of the membrane into cristae and thus for the huge increase in available surface that makes mitochondria the efficient energy plants of the eukaryotic cell.
线粒体是真核细胞的发电站，利用葡萄糖和其他糖类氧化释放的能量来产生ATP。电子从线粒体基质中柠檬酸循环产生的NADH，通过线粒体内膜中的一系列大型蛋白质复合物传递给氧气，这些复合物通过将质子泵过膜来创建跨膜电化学梯度。质子通过ATP合酶中的质子通道回流到基质中，导致核苷酸结合口袋的构象变化并形成ATP。电子传递链的三个质子泵复合物分别是NADH-泛醌氧化还原酶或复合物I、泛醌-细胞色素c氧化还原酶或复合物III以及细胞色素c氧化酶或复合物IV。琥珀酸脱氢酶或复合物II不泵质子，但提供还原型泛醌。几十年前通过X射线晶体学确定了复合物II、III和IV的结构，但直到最近，随着X射线晶体学和冷冻电子显微镜技术的进步，复合物I和ATP合酶才开始揭示它们的秘密。复合物I、III和IV在膜中一定程度上以超复合物的形式存在，即所谓的呼吸体。关于它们的功能存在几种假说。最近的冷冻电子显微镜结构以近乎原子级的细节展示了呼吸体的结构。ATP合酶在线粒体内膜中以二聚体形式存在，其曲率导致内膜折叠成嵴，从而使可用表面积大幅增加，这使得线粒体成为真核细胞高效的能量工厂。
