Buckel Wolfgang, Thauer Rudolf K
Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Str. 10, 35043 Marburg, and Fachbereich Biologie, Philipps-Universität, Marburg, Germany.
Biochim Biophys Acta. 2013 Feb;1827(2):94-113. doi: 10.1016/j.bbabio.2012.07.002. Epub 2012 Jul 16.
The review describes four flavin-containing cytoplasmatic multienzyme complexes from anaerobic bacteria and archaea that catalyze the reduction of the low potential ferredoxin by electron donors with higher potentials, such as NAD(P)H or H(2) at ≤ 100 kPa. These endergonic reactions are driven by concomitant oxidation of the same donor with higher potential acceptors such as crotonyl-CoA, NAD(+) or heterodisulfide (CoM-S-S-CoB). The process called flavin-based electron bifurcation (FBEB) can be regarded as a third mode of energy conservation in addition to substrate level phosphorylation (SLP) and electron transport phosphorylation (ETP). FBEB has been detected in the clostridial butyryl-CoA dehydrogenase/electron transferring flavoprotein complex (BcdA-EtfBC), the multisubunit [FeFe]hydrogenase from Thermotoga maritima (HydABC) and from acetogenic bacteria, the [NiFe]hydrogenase/heterodisulfide reductase (MvhADG-HdrABC) from methanogenic archaea, and the transhydrogenase (NfnAB) from many Gram positive and Gram negative bacteria and from anaerobic archaea. The Bcd/EtfBC complex that catalyzes electron bifurcation from NADH to the low potential ferredoxin and to the high potential crotonyl-CoA has already been studied in some detail. The bifurcating protein most likely is EtfBC, which in each subunit (βγ) contains one FAD. In analogy to the bifurcating complex III of the mitochondrial respiratory chain and with the help of the structure of the human ETF, we propose a conformational change by which γ-FADH(-) in EtfBC approaches β-FAD to enable the bifurcating one-electron transfer. The ferredoxin reduced in one of the four electron bifurcating reactions can regenerate H(2) or NADPH, reduce CO(2) in acetogenic bacteria and methanogenic archaea, or is converted to ΔμH(+)/Na(+) by the membrane-associated enzyme complexes Rnf and Ech, whereby NADH and H(2) are recycled, respectively. The mainly bacterial Rnf complexes couple ferredoxin oxidation by NAD(+) with proton/sodium ion translocation and the more diverse energy converting [NiFe]hydrogenases (Ech) do the same, whereby NAD(+) is replaced by H(+). Many organisms also use Rnf and Ech in the reverse direction to reduce ferredoxin driven by ΔμH(+)/Na(+). Finally examples are shown, in which the four bifurcating multienzyme complexes alone or together with Rnf and Ech are integrated into energy metabolisms of nine anaerobes. This article is part of a Special Issue entitled: The evolutionary aspects of bioenergetic systems.
这篇综述描述了来自厌氧细菌和古菌的四种含黄素的细胞质多酶复合物，它们催化低电位铁氧化还原蛋白被具有较高电位的电子供体（如NAD(P)H或≤100 kPa的H₂）还原。这些吸能反应由相同供体与较高电位受体（如巴豆酰辅酶A、NAD⁺或异二硫化物（辅酶M- S- S-辅酶B））的伴随氧化驱动。除底物水平磷酸化（SLP）和电子传递磷酸化（ETP）外，称为黄素基电子分支（FBEB）的过程可被视为能量守恒的第三种模式。FBEB已在梭菌丁酰辅酶A脱氢酶/电子传递黄素蛋白复合物（BcdA-EtfBC）、来自嗜热栖热菌（HydABC）和产乙酸细菌的多亚基[FeFe]氢化酶、产甲烷古菌的[NiFe]氢化酶/异二硫化物还原酶（MvhADG-HdrABC）以及许多革兰氏阳性和革兰氏阴性细菌及厌氧古菌的转氢酶（NfnAB）中被检测到。催化从NADH到低电位铁氧化还原蛋白以及到高电位巴豆酰辅酶A的电子分支的Bcd/EtfBC复合物已得到较为详细的研究。最有可能的分支蛋白是EtfBC，其每个亚基（βγ）都含有一个FAD。类似于线粒体呼吸链的分支复合物III，并借助人类ETF的结构，我们提出一种构象变化，通过这种变化EtfBC中的γ-FADH⁻接近β-FAD以实现分支单电子转移。在四个电子分支反应之一中被还原的铁氧化还原蛋白可以再生H₂或NADPH，在产乙酸细菌和产甲烷古菌中还原CO₂，或者通过膜相关酶复合物Rnf和Ech转化为ΔμH⁺/Na⁺，从而分别使NADH和H₂循环利用。主要存在于细菌中的Rnf复合物将NAD⁺对铁氧化还原蛋白的氧化与质子/钠离子转运偶联起来，而更为多样的能量转换[NiFe]氢化酶（Ech）也有同样作用，只是NAD⁺被H⁺取代。许多生物体还以相反方向利用Rnf和Ech由ΔμH⁺/Na⁺驱动来还原铁氧化还原蛋白。最后展示了一些例子，其中这四种分支多酶复合物单独或与Rnf和Ech一起被整合到九种厌氧菌的能量代谢中。本文是名为：生物能量系统的进化方面的特刊的一部分。
