Schäfer G, Purschke W, Schmidt C L
Institute of Biochemistry, Medical University of Lübeck, Germany.
FEMS Microbiol Rev. 1996 May;18(2-3):173-88. doi: 10.1111/j.1574-6976.1996.tb00235.x.
All aerobic organisms use the exergonic reduction of molecular oxygen to water as primary source of metabolic energy. This reaction is catalyzed by membrane residing terminal heme/Cu-oxidases which belong to a superfamily of widely varying structural complexity between mitochondrial and bacterial members of this family. Over the last few years, considerable information from this and other laboratories accumulated also on archaeal respiratory chains and their terminal oxidases. In the following, the molecular and catalytic properties of the latter are discussed and compared to those from bacteria and eucarya under the aspect of their energy conserving capabilities and their phylogenetic relations. The Rieske iron-sulfur proteins being important functional constituents of energy transducing respiratory complexes are included in this study. A number of essential conclusions can be drawn. (1) Like bacteria, archaea can also contain split respiratory chains with parallel expression of separate terminal oxidases. (2) The functional core of all oxidases is the highly conserved topological motif of subunit I consisting of at least 12 membrane spanning helices with the 6 histidine residues of the heme/Cu-binding centers in identical locations. (3) Some archaeal oxidases are organized in unusual supercomplexes with other cytochromes and Rieske [2Fe2S] proteins. These complexes are likely to function as proton pumps, whereas on a structural basis several subunit I equivalents alone are postulated to be unable to pump protons. (4) The genes of two archaeal Rieske proteins have been cloned from Sulfolobus; phylogenetically they are forming a separate archaeal branch and suggest the existence of an evolutionary ancestor preceding the split into the three urkingdoms. (5) Archaeal oxidase complexes may combine features of electron transport systems occurring exclusively as separate respiratory complexes in bacteria and eucarya. (6) As far back as the deepest branches of the phylogentic tree, terminal oxidases reveal a degree of complexity comparable to that found in higher organisms. (7) Sequence analysis suggests a monophyletic origin of terminal oxidases with an early split into two types found in archaea as well as bacteria. This view implies an origin of terminal oxidases prior to oxygenic photosynthesis in contrast to the widely accepted inverse hypothesis.
所有需氧生物都利用分子氧向水的放能还原反应作为代谢能量的主要来源。该反应由位于膜上的末端血红素/铜氧化酶催化，这些酶属于一个超家族，其线粒体成员和细菌成员在结构复杂性上差异很大。在过去几年中，来自本实验室和其他实验室的大量信息也积累在了古细菌呼吸链及其末端氧化酶方面。以下将讨论后者的分子和催化特性，并从能量保存能力及其系统发育关系方面与细菌和真核生物的特性进行比较。本研究纳入了作为能量转换呼吸复合体重要功能成分的 Rieske 铁硫蛋白。可以得出一些重要结论。（1）与细菌一样，古细菌也可能含有分裂的呼吸链，同时表达不同的末端氧化酶。（2）所有氧化酶的功能核心是亚基 I 高度保守的拓扑基序，由至少 12 个跨膜螺旋组成，血红素/铜结合中心的 6 个组氨酸残基位于相同位置。（3）一些古细菌氧化酶与其他细胞色素和 Rieske [2Fe2S] 蛋白组装成不同寻常的超复合体。这些复合体可能起到质子泵的作用，而仅从结构上看，几个亚基 I 等同物被认为无法泵送质子。（4）已从古生球菌中克隆出两种古细菌 Rieske 蛋白的基因；从系统发育角度来看，它们形成了一个独立的古细菌分支，表明在分化为三个原核生物界之前存在一个进化祖先。（5）古细菌氧化酶复合体可能兼具仅在细菌和真核生物中作为独立呼吸复合体出现的电子传递系统的特征。（6）早在系统发育树的最深分支处，末端氧化酶就显示出与高等生物中相当的复杂程度。（7）序列分析表明末端氧化酶起源于单系，早期分为在古细菌和细菌中都存在的两种类型。这一观点意味着末端氧化酶起源于光合放氧之前，这与广泛接受的相反假设不同。
