Max-Planck-Institut für Biophysik, Max-von-Laue-Str. 3, 60438, Frankfurt am Main, Germany.
Laboratorium für Mikrobiologie, Fachbereich Biologie and SYNMIKRO, Philipps-Universität, 35032, Marburg, Germany.
Nat Commun. 2017 Nov 17;8(1):1577. doi: 10.1038/s41467-017-01746-3.
The electron transferring flavoprotein/butyryl-CoA dehydrogenase (EtfAB/Bcd) catalyzes the reduction of one crotonyl-CoA and two ferredoxins by two NADH within a flavin-based electron-bifurcating process. Here we report on the X-ray structure of the Clostridium difficile (EtfAB/Bcd) complex in the dehydrogenase-conducting D-state, α-FAD (bound to domain II of EtfA) and δ-FAD (bound to Bcd) being 8 Å apart. Superimposing Acidaminococcus fermentans EtfAB onto C. difficile EtfAB/Bcd reveals a rotation of domain II of nearly 80°. Further rotation by 10° brings EtfAB into the bifurcating B-state, α-FAD and β-FAD (bound to EtfB) being 14 Å apart. This dual binding mode of domain II, substantiated by mutational studies, resembles findings in non-bifurcating EtfAB/acyl-CoA dehydrogenase complexes. In our proposed mechanism, NADH reduces β-FAD, which bifurcates. One electron goes to ferredoxin and one to α-FAD, which swings over to reduce δ-FAD to the semiquinone. Repetition affords a second reduced ferredoxin and δ-FADH, which reduces crotonyl-CoA.
电子转移黄素蛋白/丁酰基辅酶 A 脱氢酶（EtfAB/Bcd）在黄素基电子分叉过程中催化一个丁烯酰辅酶 A 和两个还原型铁氧还蛋白被两个 NADH 还原。在这里，我们报告了艰难梭菌（EtfAB/Bcd）复合物在脱氢酶传导 D 态的 X 射线结构，α-FAD（与 EtfA 的结构域 II 结合）和 δ-FAD（与 Bcd 结合）相距 8Å。将 Acidaminococcus fermentans EtfAB 叠加到 C. difficile EtfAB/Bcd 上，揭示了结构域 II 的近 80°的旋转。再旋转 10°将 EtfAB 带入分叉的 B 态，α-FAD 和 β-FAD（与 EtfB 结合）相距 14Å。这种结构域 II 的双重结合模式，通过突变研究得到了证实，类似于非分叉 EtfAB/酰基辅酶 A 脱氢酶复合物的发现。在我们提出的机制中，NADH 还原 β-FAD，使其分叉。一个电子转移到铁氧还蛋白，另一个电子转移到 α-FAD，α-FAD 摆动以将 δ-FAD 还原为半醌。重复这一过程可提供第二个还原的铁氧还蛋白和 δ-FADH，还原丁烯酰辅酶 A。
