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首页> 外文期刊>Biochemistry >Interactions between the cytochrome b, cytochrome c(1), and Fe-S protein subunits at the ubihydroquinone oxidation site of the bc(1) complex of Rhodobacter capsulatus
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Interactions between the cytochrome b, cytochrome c(1), and Fe-S protein subunits at the ubihydroquinone oxidation site of the bc(1) complex of Rhodobacter capsulatus

机译：细胞色素b，细胞色素c（1）和Fe-S蛋白亚基在荚膜红细菌bc（1）复合物的泛氢醌氧化位点之间的相互作用

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摘要

Ubihydroquinone:cytochrome (cyt) c oxidoreductase (bc(1) complex and its plant counterpart b(6)f complex) is a vital component of energy-transducing systems in most organisms from bacteria to eukaryotes. In the facultative phototrophic (Ps) bacterium Rhodobacter capsulatus, it is constituted by the cyt b, cyt c(1), and Rieske Fe-S protein subunits and is essential for Ps growth. Of these subunits, cyt b has two nontransmembrane helices, cd1 and cd2, which are critical for its structure and function. In particular, substitution of threonine (T) at position 163 on cd1 with phenylalanine (F) or proline (P) leads to the absence of the bc(1) complex. Here, Ps(+) revertants of B:T163F were obtained, and their detailed characterizations indicated that position 163 is important for the assembly of the bc(1) complex by mediating subunit interactions at the Q(o) site. The loss of the hydroxyl group at position 163 of cyt b was compensated for by the gain of either a hydroxyl group at position 182 of cyt b or 46 of the Fe-S protein or a sulfhydryl group at position 46 of cyt c(1). Examination of the mitochondrial bc(1) complex crystal structure [Zhang, Z., Huang, L., Shulmeister, V. M., Chi, Y.-I,, Kim, K. K., Hung, L.-W., Crofts, A. R., Berry, E. A., and Kim, S.-H. (1998) Nature 392, 677-684] revealed that the counterparts of B:G182 (i.e., G167) and F:A46 (i.e., A70) are located close to B:T163 (i.e., T148), whereas the C:R46 (i.e., R28) is remarkably far from it. The revertants contained substoichiometric amounts of the Fe-S protein subunit and exhibited steady-state and single-turnover, electron transfer activities lower than that of a wild-type bc(1) complex. Interestingly, their membrane supernatants contained a smaller form of this subunit with physicochemical properties identical to those of its membrane-bound form. Determination of the amino-terminal amino acid sequence of this soluble Fe-S protein revealed that it was derived from the wild-type protein by proteolytic cleavage at V44. This work revealed for the first time that position 163 of cyt b is important both for proper subunit interactions at the Q(o) site and for inactivation of the bc(1) complex by proteolytic cleavage of its Fe-S protein subunit at a region apparently responsible for its mobility during Q(o) site catalysis. [References: 45]
机译：泛氢醌：细胞色素（cyt）c氧化还原酶（bc（1）复合物及其对应的b（6）f复合物）是从细菌到真核生物的大多数生物体中能量转换系统的重要组成部分。在兼性的光养（Ps）细菌荚膜红细菌中，它由cyt b，cyt c（1）和Rieske Fe-S蛋白亚基组成，对Ps的生长至关重要。在这些亚基中，cyt b具有两个非跨膜螺旋cd1和cd2，这对其结构和功能至关重要。特别是，用苯丙氨酸（F）或脯氨酸（P）取代cd1上163位的苏氨酸（T）导致不存在bc（1）复合物。在这里，获得了B：T163F的Ps（+）还原体，其详细特征表明位置163对于介导Q（o）部位的亚基相互作用对于bc（1）配合物的组装很重要。 cyt b位置163处羟基的丢失可通过cyt b的182位处的羟基或Fe-S蛋白46的获得或cyt c（1）的4​​6位处的巯基获得补偿。 。线粒体bc（1）复杂晶体结构的检验[Zhang，Z.，Huang，L.，Shulmeister，VM，Chi，Y.-I，Kim，KK，Hung，L.-W.，Crofts，AR， EA的Berry和S.-H的Kim （1998）Nature 392，677-684]揭示B：G182（即G167）和F：A46（即A70）的对应物靠近B：T163（即T148），而C：R46 （即R28）距离它很远。还原剂包含亚化学计量的Fe-S蛋白亚基，并表现出稳态和单周转，电子传递活性低于野生型bc（1）复合物。有趣的是，它们的膜上清液包含较小形式的该亚基，其物理化学性质与其膜结合形式相同。对这种可溶性Fe-S蛋白的氨基末端氨基酸序列的测定表明，它是通过在V44处的蛋白水解切割而衍生自野生型蛋白的。这项工作首次揭示了cyt b的163位对于Q（o）位点的正确亚基相互作用以及通过蛋白水解其区域的Fe-S蛋白亚基使bc（1）复合物失活都非常重要。显然是其在Q（o）部位催化过程中的流动性负责[参考：45]

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