Zu Yanbing, Couture Manon M-J, Kolling Derrick R J, Crofts Antony R, Eltis Lindsay D, Fee James A, Hirst Judy
Medical Research Council Dunn Human Nutrition Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 2XY, United Kingdom.
Biochemistry. 2003 Oct 28;42(42):12400-8. doi: 10.1021/bi0350957.
Rieske [2Fe-2S] clusters can be classified into two groups, depending on their reduction potentials. Typical high-potential Rieske proteins have pH-dependent reduction potentials between +350 and +150 mV at pH 7, and low-potential Rieske proteins have pH-independent potentials of around -150 mV at pH 7. The pH dependence of the former group is attributed to coupled deprotonation of the two histidine ligands. Protein-film voltammetry has been used to compare three Rieske proteins: the high-potential Rieske proteins from Rhodobacter sphaeroides (RsRp) and Thermus thermophilus (TtRp) and the low-potential Rieske ferredoxin from Burkholderia sp. strain LB400 (BphF). RsRp and TtRp differ because there is a cluster to serine hydrogen bond in RsRp, which raises its potential by 140 mV. BphF lacks five hydrogen bonds to the cluster and an adjacent disulfide bond. Voltammetry measurements between pH 3 and 14 reveal that all the proteins, including BphF, have pH-dependent reduction potentials with remarkably similar overall profiles. Relative to RsRp and TtRp, the potential versus pH curve of BphF is shifted to lower potential and higher pH, and the pK(a) values of the histidine ligands of the oxidized and reduced cluster are closer together. Therefore, in addition to simple electrostatic effects on E and pK(a), the reduction potentials of Rieske clusters are determined by the degree of coupling between cluster oxidation state and histidine protonation state. Implications for the mechanism of quinol oxidation at the Q(O) site of the cytochrome bc(1) and b(6)f complexes are discussed.
根据还原电位， Rieske [2Fe-2S] 簇可分为两组。典型的高电位 Rieske 蛋白在 pH 7 时具有 pH 依赖性还原电位，范围在 +350 至 +150 mV 之间，而低电位 Rieske 蛋白在 pH 7 时具有约 -150 mV 的 pH 非依赖性电位。前一组的 pH 依赖性归因于两个组氨酸配体的偶联去质子化。蛋白质膜伏安法已用于比较三种 Rieske 蛋白：来自球形红杆菌（RsRp）和嗜热栖热菌（TtRp）的高电位 Rieske 蛋白以及来自伯克霍尔德菌属 LB400 菌株（BphF）的低电位 Rieske 铁氧还蛋白。RsRp 和 TtRp 不同，因为 RsRp 中存在簇与丝氨酸的氢键，这使其电位提高了 140 mV。BphF 缺乏与簇的五个氢键和一个相邻的二硫键。在 pH 3 至 14 之间的伏安法测量表明，所有蛋白质，包括 BphF，都具有 pH 依赖性还原电位，其总体轮廓非常相似。相对于 RsRp 和 TtRp，BphF 的电位与 pH 曲线向更低电位和更高 pH 移动，并且氧化态和还原态簇的组氨酸配体的 pK(a) 值更接近。因此，除了对 E 和 pK(a) 的简单静电效应外，Rieske 簇的还原电位还由簇氧化态和组氨酸质子化态之间的偶联程度决定。讨论了对细胞色素 bc(1) 和 b(6)f 复合物的 Q(O) 位点喹啉氧化机制的影响。
