Assignment of the histidine axial ligands to the cytochrome bH and cytochrome bL components of the bc1 complex from Rhodobacter sphaeroides by site-directed mutagenesis.
Assignment of the histidine axial ligands to the cytochrome bH and cytochrome bL components of the bc1 complex from Rhodobacter sphaeroides by site-directed mutagenesis.
复制标题
通过定点诱变将组氨酸轴向配体分配给来自球形红杆菌的 bc1 复合物的细胞色素 bH 和细胞色素 bL 成分。
DOI：
10.1021/bi00241a017
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发表时间：
1991
期刊：
影响因子：
2.9
通讯作者：
Gennis,RB
中科院分区：
文献类型：
--
作者：
Yun,CH;Crofts,AR;Gennis,RB
bcx复合物的细胞色素b亚基含有两种细胞色素成分，细胞色素bH和细胞色素bL。对来自许多生物体的这种多肽的序列比较揭示了四种不变组氨酸，它们被认为是两个原血红素IX假基的血红素配体。在球形红杆菌中，这些对应于His97、his11、his98和His212。在本文中，报告了在这些位置上的氨基酸取代的结果。用Asp或Asn代替His97，用Asn或Tyr代替His 198，导致两种细胞色素成分的损失。然而，Hisl 11asn、Hisl 1lasp和His212Asp都导致细胞色素bH的选择性损失和细胞色素b的保留。此外，闪变动力学研究表明，与细胞色素bL相关的粘噻唑敏感喹诺氧化酶（Qz）位点仍然具有功能。这些数据支持轴向配体分配给细胞色素bH （Hisl 11和His212）和细胞色素bL （His97和his98）。这种配对与目前具有8个跨膜a-螺旋的细胞色素b亚基模型一致。泛醇木色素c氧化还原酶，也称为bcx复合物，是线粒体、叶绿体（其中称为b6/f复合物）和细菌的节能电子传递链的核心成分（Gabellini, 1988; Hauska et al., 1988; Crofts, 1985）。本研究由美国国立卫生研究院资助（GM35438给RBG和ARC， GM26305给ARC）。信件应寄给谁。1北京大学生理与生物物理系；•生物化学与化学系。复合物具有显著的结构和功能相似性。所有bcx（和bj）复合物都含有一个细胞铬b亚基，该亚基似乎是醌氧化酶位点（Qz或Q0）和醌还原酶位点（Qc或Q；）的主要结构元件。在所有的bcx和bf配合物中发现了具有不同中点电位（bL和bH）的两种光谱上不同的细胞色素b组分。在提出的q -循环机制(Mitchell, 1976; Crofts，
The cytochrome b subunit of the bcx complex contains two cytochrome components, cytochrome bH and cytochrome bL. Sequence comparisons of this polypeptide from a number of organisms have revealed four invariant histidines which have been postulated to be the heme ligands for the two protoheme IX prosthetic groups. In Rhodobacter sphaeroides, these correspond to His97, Hisl 11, Hisl98, and His212. In this paper, the results of amino acid substitutions at each of these positions are reported. Replacement of His97 by either Asp or Asn and of His 198 by Asn or Tyr resulted in loss of both cytochrome components. However, Hisl 11 Asn, Hisl 1 lAsp, and His212Asp all resulted in theselective loss of cytochrome bH and the retention of cytochrome b\_. Furthermore, flash kinetics studies show that the myxothiazol-sensitive quinol oxidase (Qz) site associated with cytochrome bL is still functional. These data support the assignment of the axial ligands to cytochrome bH (Hisl 11 and His212) and cytochrome bL (His97 and Hisl98). This pairing is consistent with current models of the cytochrome b subunit with eight transmembrane a-helices. e ubiquinolxytochrome c oxidoreductases, also known as the bcx complexes, are central components in the energyconserving electron-transfer chains of mitochondria, chloro-plasts (where it is known as the b6/f complex), and bacteria (Gabellini, 1988; Hauska et al., 1988; Crofts, 1985). These fThis research was supported by grants from the National Institutes of Health (GM35438 to RBG and ARC and GM26305 to ARC).* To whom correspondence should be addressed. 1 Department of Physiology and Biophysics.• Department of Biochemistry and Chemistry. complexes manifest remarkable structural and functional similarities. All the bcx (and bj) complexes contain a cyto-chrome b subunit which appears to contribute major structural elements of both a quinol oxidase site (Qz or Q0) and a quinone reductase site (Qc or Q;). Two spectroscopically distinct cytochrome b components with different midpoint potentials (bL and bH) are found in all the bcx and bf complexes. In a proposed Q-cycle mechanism (Mitchell, 1976; Crofts,