Structural basis for the quinone reduction in the bc1 complex:: A comparative analysis of crystal structures of mitochondrial cytochrome bc1 with bound substrate and inhibitors at the Qi site
Structural basis for the quinone reduction in the bc1 complex:: A comparative analysis of crystal structures of mitochondrial cytochrome bc1 with bound substrate and inhibitors at the Qi site
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DOI：
10.1021/bi0341814
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发表时间：
2003-08-05
期刊：
影响因子：
2.9
通讯作者：
Xia, D
中科院分区：
文献类型：
--
作者：
Gao, XG;Wen, XL;Xia, D
细胞色素bc（1）是细胞呼吸和光合作用所必需的膜蛋白复合体。bc（1）的Q循环反应机理假定了一个分离的醌还原（Q（i））和醌醇氧化（Q（i））位点。在一个完整的催化循环中，Q（i）位点的醌分子从B（H）血红素接收两个电子，从膜的负侧接收两个质子;该过程被抗霉素A和NQNO特异性抑制。牛线粒体bc（1）在存在或不存在结合底物泛醌以及结合抗霉素A（1）或NQNO的情况下的结构被确定和改进。在底物和抑制剂结合结构的Q（i）口袋中分别鉴定了具有前两个类异戊二烯重复序列的泛醌和抗霉素A（1）;另一方面，在抑制剂复合物的Q（i）和Q（o）口袋中鉴定了NQNO。这两种抑制剂占据了Q（i）口袋的不同部分，并与底物竞争结合。在Q（i）口袋中，NQNO的行为类似于stigmatellin，诱导铁硫蛋白构象停滞。广泛的结合相互作用和构象调整的残基衬里的Q（i）口袋提供了高亲和力结合的抗霉素A和抑制剂抗性的表型的结构基础。提出了一种两水介导的泛醌质子化机制，涉及三个Q（i）位点残基His（201），Lys（227）和Asp（228）。
Cytochrome bc(1) is an integral membrane protein complex essential to cellular respiration and photosynthesis. The Q cycle reaction mechanism of bc(1) postulates a separated quinone reduction (Q(i)) and quinol oxidation (Q(i)) site. In a complete catalytic cycle, a quinone molecule at the Q(i) site receives two electrons from the b(H) heme and two protons from the negative side of the membrane; this process is specifically inhibited by antimycin A and NQNO. The structures of bovine mitochondrial bc(1) in the presence or absence of bound substrate ubiquinone and with either the bound antimycin A(1) or NQNO were determined and refined. A ubiquinone with its first two isoprenoid repeats and an antimycin A(1) were identified in the Q(i) pocket of the substrate and inhibitor bound structures, respectively; the NQNO, on the other hand, was identified in both Q(i) and Q(o) pockets in the inhibitor complex. The two inhibitors occupied different portions of the Q(i) pocket and competed with substrate for binding. In the Q(i) pocket, the NQNO behaves similarly to stigmatellin, inducing an iron-sulfur protein conformational arrest. Extensive binding interactions and conformational adjustments of residues lining the Q(i) pocket provide a structural basis for the high affinity binding of antimycin A and for phenotypes of inhibitor resistance. A two-water-mediated ubiquinone protonation mechanism is proposed involving three Q(i) site residues His(201), Lys(227), and Asp(228).