Kim H, Xia D, Yu C A, Xia J Z, Kachurin A M, Zhang L, Yu L, Deisenhofer J
Howard Hughes Medical Institute and Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75235-9050, USA.
Proc Natl Acad Sci U S A. 1998 Jul 7;95(14):8026-33. doi: 10.1073/pnas.95.14.8026.
We have analyzed crystal structures of cytochrome bc1 complexes with electron transfer inhibitors bound to the ubiquinone binding pockets Qi and/or Qo in the cytochrome b subunit. The presence or absence of the Qi inhibitor antimycin A did not affect the binding of the Qo inhibitors. Different subtypes of Qo inhibitors had dramatically different effects on the mobility of the extramembrane domain of the iron-sulfur protein (ISP): Binding of 5-undecyl-6-hydroxy-4, 7-dioxobenzothiazol and stigmatellin (subtype Qo-II and Qo-III, respectively) led to a fixation of the ISP domain on the surface of cytochrome b, whereas binding of myxothiazol and methoxyacrylate-stilbene (subtype Qo-I) favored release of this domain. The native structure has an empty Qo pocket and is intermediate between these extremes. On the basis of these observations we propose a model of quinone oxidation in the bc1 complex, which incorporates fixed and loose states of the ISP as features important for electron transfer and, possibly, also proton transport.
我们分析了细胞色素bc1复合物的晶体结构，这些复合物中电子传递抑制剂与细胞色素b亚基中的泛醌结合口袋Qi和/或Qo结合。Qi抑制剂抗霉素A的存在与否不影响Qo抑制剂的结合。不同亚型的Qo抑制剂对铁硫蛋白（ISP）膜外结构域的流动性有显著不同的影响：5-十一烷基-6-羟基-4,7-二氧代苯并噻唑和柱晶白霉素（分别为Qo-II和Qo-III亚型）的结合导致ISP结构域固定在细胞色素b表面，而粘噻唑和甲氧基丙烯酸酯-芪（Qo-I亚型）的结合则有利于该结构域的释放。天然结构的Qo口袋是空的，处于这两种极端情况之间。基于这些观察结果，我们提出了bc1复合物中醌氧化的模型，该模型将ISP的固定态和松散态纳入其中，作为对电子传递以及可能对质子转运都很重要的特征。
