García-Trejo José J, Morales-Ríos Edgar
Facultad de Química, Departamento de Biología, Lab. F-117, Universidad Nacional Autónoma de México, México, D.F., 04510, México.
J Biol Phys. 2008 Apr;34(1-2):197-212. doi: 10.1007/s10867-008-9114-z. Epub 2008 Oct 4.
The F(1)F(0)-adenosine triphosphate (ATP) synthase rotational motor synthesizes most of the ATP required for living from adenosine diphosphate, Pi, and a proton electrochemical gradient across energy-transducing membranes of bacteria, chloroplasts, and mitochondria. However, as a reversible nanomotor, it also hydrolyzes ATP during de-energized conditions in all energy-transducing systems. Thus, different subunits and mechanisms have emerged in nature to control the intrinsic rotation of the enzyme to favor the ATP synthase activity over its opposite and commonly wasteful ATPase turnover. Recent advances in the structural analysis of the bacterial and mitochondrial ATP synthases are summarized to review the distribution and mechanism of the subunits that are part of the central rotor and regulate its gyration. In eubacteria, the epsilon subunit works as a ratchet to favor the rotation of the central stalk in the ATP synthase direction by extending and contracting two alpha-helixes of its C-terminal side and also by binding ATP with low affinity in thermophilic bacteria. On the other hand, in bovine heart mitochondria, the so-called inhibitor protein (IF(1)) interferes with the intrinsic rotational mechanism of the central gamma subunit and with the opening and closing of the catalytic beta-subunits to inhibit its ATPase activity. Besides its inhibitory role, the IF(1) protein also promotes the dimerization of the bovine and rat mitochondrial enzymes, albeit it is not essential for dimerization of the yeast F(1)F(0) mitochondrial complex. High-resolution electron microscopy of the dimeric enzyme in its bovine and yeast forms shows a conical shape that is compatible with the role of the ATP synthase dimer in the formation of tubular the cristae membrane of mitochondria after further oligomerization. Dimerization of the mitochondrial ATP synthase diminishes the rotational drag of the central rotor that would decrease the coupling efficiency between rotation of the central stalk and ATP synthesis taking place at the F(1) portion. In addition, F(1)F(0) dimerization and its further oligomerization also increase the stability of the enzyme to natural or experimentally induced destabilizing conditions.
F(1)F(0)-三磷酸腺苷（ATP）合酶旋转马达利用二磷酸腺苷、磷酸以及细菌、叶绿体和线粒体能量转换膜上的质子电化学梯度合成生命所需的大部分ATP。然而，作为一种可逆的纳米马达，在所有能量转换系统的能量耗尽条件下，它也会水解ATP。因此，自然界中出现了不同的亚基和机制来控制该酶的固有旋转，以利于ATP合酶活性，而非其相反且通常浪费的ATP酶周转。本文总结了细菌和线粒体ATP合酶结构分析的最新进展，以综述作为中央转子一部分并调节其旋转的亚基的分布和机制。在真细菌中，ε亚基起到棘轮的作用，通过其C端的两个α螺旋的伸展和收缩，以及在嗜热细菌中以低亲和力结合ATP，来促进中央轴在ATP合酶方向上的旋转。另一方面，在牛心线粒体中，所谓的抑制蛋白（IF(1)）干扰中央γ亚基的固有旋转机制以及催化β亚基的开闭，从而抑制其ATP酶活性。除了其抑制作用外，IF(1)蛋白还促进牛和大鼠线粒体酶的二聚化，尽管它对于酵母F(1)F(0)线粒体复合物的二聚化并非必需。牛和酵母形式的二聚体酶的高分辨率电子显微镜显示出一种圆锥形，这与ATP合酶二聚体在进一步寡聚化后在线粒体内嵴膜形成中的作用相符。线粒体ATP合酶的二聚化减少了中央转子的旋转阻力，否则这会降低中央轴旋转与F(1)部分ATP合成之间的耦合效率。此外，F(1)F(0)二聚化及其进一步的寡聚化也增加了酶对自然或实验诱导的不稳定条件的稳定性。
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