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首页> 外文期刊>Biochemistry >Substitution of the sixth axial ligand of Rhodobacter capsulatus cytochrome c1 heme yields novel cytochrome c1 variants with unusual properties.
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Substitution of the sixth axial ligand of Rhodobacter capsulatus cytochrome c1 heme yields novel cytochrome c1 variants with unusual properties.

机译：荚膜红细菌细胞色素c1血红素的第六个轴向配体的替代产生具有异常特性的新型细胞色素c1变体。

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摘要

The cytochrome (cyt) c1 heme of the ubihydroquinone:cytochrome c oxidoreductase (bc1 complex) is covalently attached to two cysteine residues of the cyt c1 polypeptide chain via two thioether bonds, and the fifth and sixth axial ligands of its iron atom are histidine (H) and methionine (M), respectively. The latter residue is M183 in Rhodobacter capsulatus cyt c1, and previous mutagenesis studies revealed its critical role for the physicochemical properties of cyt c1 [Gray, K. A., Davidson, E., and Daldal, F. (1992) Biochemistry 31, 11864-11873]. In the homologous chloroplast b6f complex, the sixth axial ligand is provided by the amino group of the amino terminal tyrosine residue. To further pursue our investigation on the role played by the sixth axial ligand in heme-protein interactions, novel cyt c1 variants with histidine-lysine (K) and histidine-histidine axial coordination were sought. Using a R. capsulatus genetic system, the cyt c1 mutants M183K and M183H were constructed by site-directed mutagenesis, and chromatophore membranes as well as purified bc1 complexes obtained from these mutants were characterized in detail. The studies revealed that these mutants incorporated the heme group into the mature cyt c1 polypeptides, but yielded nonfunctional bc1 complexes with unusual spectroscopic and thermodynamic properties, including shifted optical absorption maxima (lambdamax) and decreased redox midpoint potential values (Em7). The availability and future detailed studies of these stable cyt c1 mutants should contribute to our understanding of how different factors influence the physicochemical and folding properties of membrane-bound c-type cytochromes in general.
机译：泛氢醌：细胞色素c氧化还原酶（bc1复合物）的细胞色素（cyt）c1血红素通过两个硫醚键共价连接到cyt c1多肽链的两个半胱氨酸残基上，其铁原子的第五和第六轴向配体为组氨酸（ H）和蛋氨酸（M）。后者的残基是荚膜红球菌cyt c1中的M183，先前的诱变研究揭示了其对cyt c1的理化特性的关键作用[Gray，KA，Davidson，E.和Daldal，F.（1992）Biochemistry 31，11864-11873 ]。在同源叶绿体b6f复合物中，第六轴向配体由氨基末端酪氨酸残基的氨基提供。为了进一步研究第六轴配体在血红素-蛋白质相互作用中的作用，寻找具有组氨酸-赖氨酸（K）和组氨酸-组氨酸轴向配位的新型cyt c1变体。使用荚膜芽孢杆菌遗传系统，通过定点诱变构建cyt c1突变体M183K和M183H，并详细描述了从这些突变体获得的色谱膜以及纯化的bc1复合物。研究表明，这些突变体将血红素基团整合到成熟的cyt c1多肽中，但产生具有异常光谱和热力学特性的非功能性bc1复合物，包括最大的光吸收位移（lambdamax）和降低的氧化还原中点电位值（Em7）。这些稳定的cyt c1突变体的可用性和未来的详细研究应有助于我们理解不同因素通常如何影响膜结合的c型细胞色素的理化和折叠特性。

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