Coupling H+ transport and ATP synthesis in F1F0-ATP synthases: glimpses of interacting parts in a dynamic molecular machine.
Coupling H+ transport and ATP synthesis in F1F0-ATP synthases: glimpses of interacting parts in a dynamic molecular machine.
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发表时间：
1997
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通讯作者：
R. H. Fillingame
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作者：
R. H. Fillingame
可逆的F1 F0型ATP酶（也称为F-ATP酶）在氧化磷酸化过程中催化ATP的合成。在动物细胞中，这种酶穿过线粒体内膜，并利用电子传递产生的H+电化学梯度的能量，将H+易位与ATP形成偶联。在细菌如大肠杆菌的质膜中发现了密切相关的酶，其中酶根据营养环境可逆地发挥作用。F1 F0型酶与第二个H（+）转运ATP酶家族（液泡型或V-ATP酶）的亲缘关系较远。最近的结构信息提供了重要的提示，这些酶如何耦合H+运输的ATP合成的化学工作。最简单的F1 F0型酶，例如在E.大肠杆菌中，由八种不同的亚基组成，其化学计量比为α 3 β 3 γ δ 12（F1）和a1 b2 c12（F0）。F1从膜延伸，α和β亚基围绕中心亚基γ交替。ATP的合成在不同的β亚基中交替发生，ADP + Pi在一个催化位点的紧密结合与ATP在第二个催化位点的释放相耦合。结合亲和力的差异似乎是由α 3 β 3六聚体中心γ亚基的旋转引起的。γ亚基穿过将催化亚基连接到膜穿越F0扇区的4.5 nm茎。亚基c是F0的H（+）-易位亚基。Asp 61在膜中心的质子化/去质子化与亚基c的膜外环中的结构变化偶联，亚基c与γ亚基和γ亚基相互作用。当ATP合成时，γ亚基和γ亚基似乎从一个c亚基移动到另一个。这种运动的扭矩被认为是导致α 3 β 3复合体中γ的旋转。每合成一个ATP，就有四个质子移位。因此，γ和β的运动可能涉及一个由四个c亚基组成的单位。F0中亚基的组织仍然是一个谜;如果我们要了解扭矩产生的机制，就必须了解它。
Reversible, F1F0-type ATPases (also termed F-ATP synthases) catalyze the synthesis of ATP during oxidative phosphorylation. In animal cells, the enzyme traverses the inner mitochondrial membrane and uses the energy of an H+ electrochemical gradient, generated by electron transport, in coupling H+ translocation to ATP formation. Closely related enzymes are found in the plasma membrane of bacteria such as Escherichia coli, where the enzymes function reversibly depending upon nutritional circumstance. The F1F0-type enzymes are more distantly related to a second family of H(+)-translocating ATPases, the vacuolar-type or V-ATPases. Recent structural information has provided important hints as to how these enzymes couple H+ transport to the chemical work of ATP synthesis. The simplest F1F0-type enzymes, e.g. as in E. coli, are composed of eight types of subunits in an unusual stoichiometry of alpha 3 beta 3 gamma delta epsilon (F1) and a1b2c12 (F0). F1 extends from the membrane, with the alpha and beta subunits alternating around a central subunit gamma. ATP synthesis occurs alternately in different beta subunits, the cooperative tight binding of ADP + Pi at one catalytic site being coupled to ATP release at a second. The differences in binding affinities appear to be caused by rotation of the gamma subunit in the center of the alpha 3 beta 3 hexamer. The gamma subunit traverses a 4.5 nm stalk connecting the catalytic subunits to the membrane-traversing F0 sector. Subunit c is the H(+)-translocating subunit of F0. Protonation/deprotonation of Asp61 in the center of the membrane is coupled to structural changes in an extramembranous loop of subunit c which interacts with both the gamma and epsilon subunits. Subunits gamma and epsilon appear to move from one subunit c to another as ATP is synthesized. The torque of such movement is proposed to cause the rotation of gamma within the alpha 3 beta 3 complex. Four protons are translocated for each ATP synthesized. The movement of gamma and epsilon therefore probably involves a unit of four c subunits. The organization of subunits in F0 remains a mystery; it will have to be understood if we are to understand the mechanism of torque generation.