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首页> 外文期刊>Biochemistry >Intermonomer Electron Transfer between the Low-Potential b Hemes of Cytochrome bc_1
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Intermonomer Electron Transfer between the Low-Potential b Hemes of Cytochrome bc_1

机译：细胞色素bc_1的低电势血红素之间的单体间电子转移

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摘要

Cytochrome (cyt) bc_1 is a structural dimer with its monomers consisting of the Fe-S protein, cyt b, and cyt c_1 subunits. Its three-dimensional architecture depicts it as a symmetrical homodimer, but the mobility of the head domain of the Fe-S protein indicates that the functional enzyme exists in asymmetrical heterodimeric conformations. Here, we report a new genetic system for studying intra- and intermonomer interactions within the cyt bc_1 using the facultative phototrophic bacterium Rhodobacter capsulatus. The system involves two different sets of independently expressed cyt bc_1 structural genes carried by two plasmids that are coharbored by a cell without its endogenous enzyme. Our results indicate that coexpressed cyt bc_1 subunits were matured, assorted, and assembled in vivo into homo- and heterodimeric enzymes that can bear different mutations in each monomer. Using the system, the occurrence of intermonomer electron transfer between the low-potential b hemes of cyt bc_1 was probed by choosing mutations that perturb electron transfer at the hydroquinone oxidation (Q_o) and quinone reduction (Q_i) sites of the enzyme. The data demonstrate that active heterodimeric variants, formed of monomers carrying mutations that abolish only one of the two (Q_o or Q_i) active sites of each monomer, are produced, and they support photosynthetic growth of R. capsulatus. Detailed analyses of the physicochemical properties of membranes of these mutants, as well as purified homo- and heterodimeric cyt bc_1 preparations, demonstrated that efficient and productive electron transfer occurs between the low-potential b_L, hemes of the monomers in a heterodimeric enzyme. Overall findings are discussed with respect to intra- and intermonomer interactions that take place during the catalytic turnover of cyt bc_1.
机译：细胞色素（cyt）bc_1是一种结构二聚体，其单体由Fe-S蛋白，cyt b和cyt c_1亚基组成。它的三维结构将其描述为对称的同型二聚体，但Fe-S蛋白头部结构域的迁移性表明功能性酶以不对称的异二聚体构象存在。在这里，我们报告了一个新的遗传系统，用于研究使用兼性的光养细菌荚膜红细菌，在cyt bc_1内和单体之间的相互作用。该系统涉及由两个质粒携带的两组不同的独立表达的cyt bc_1结构基因，这两个质粒被没有其内源酶的细胞共同携带。我们的结果表明，共表达的cyt bc_1亚基在体内成熟，分类并组装成同型和异型二聚体酶，每个单体中都可以具有不同的突变。使用该系统，通过选择扰动酶在氢醌氧化（Q_o）和醌还原（Q_i）位的电子转移的突变，来探测cyt bc_1的低电势血红素之间的单体电子转移的发生。数据证明产生了由带有突变的单体形成的活性异二聚体变体，所述突变仅消除了每个单体的两个（Q_o或Q_i）活性位点之一，并且它们支持荚膜红球菌的光合生长。对这些突变体以及纯化的同型和异型二聚体cyt bc_1制剂的膜的理化性质的详细分析表明，异型二聚酶中单体的低电位b_L，血红素之间发生了有效且高效的电子转移。关于胞内bc_1催化转换期间发生的单体内和单体间相互作用的整体发现进行了讨论。

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