Structural Evidence for the Functional Importance of the Heme Domain Mobility in Flavocytochrome b2
Structural Evidence for the Functional Importance of the Heme Domain Mobility in Flavocytochrome b2
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DOI：
10.1016/j.jmb.2010.05.035
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发表时间：
2010-07-16
影响因子：
5.6
通讯作者：
Golinelli-Pimpaneau, Beatrice
中科院分区：
文献类型：
--
作者：
Le, K. H. Diep;Lederer, Florence;Golinelli-Pimpaneau, Beatrice
酵母黄素细胞色素 b(2) (Fcb2) 是一种 L-乳酸：细胞色素 c 氧化还原酶，位于线粒体膜间隙中，参与细胞呼吸。每个酶亚基由细胞色素 b(5) 样血红素结构域和黄素脱氢酶 (FDH) 结构域组成。在 Fcb2 晶体结构中，血红素结构域在两个亚基之一中相对于四聚体 FDH 核心是可移动的。针对全酶引发的单克隆抗体 B2B4 仅识别全酶中的天然血红素结构域。结合后，它会抑制从黄素到血红素 b(2) 的分子内电子转移，从而减少细胞色素 c。我们在此报告了与 Fab 复合的血红素结构域的晶体结构，分辨率为 2.7 埃。血红素结构域上的 Fab 表位包括血红素的两个暴露的丙酸酯基团，它们隐藏在完整亚基中结构域之间的界面中。该结构揭示了 Fcb2 在血红素腔附近具有意想不到的可塑性，其中血红素已旋转。该表位与 FDH 结构域在血红素结构域上的对接区域重叠，表明抗体以大幅度的移动取代了血红素结构域。我们认为细胞色素c的血红素结构域和FDH结构域的结合位点也重叠，因此细胞色素c的结合也需要血红素结构域移离FDH结构域，以便允许两个血红素之间的电子转移。基于这一假设，我们提出了 Fcb2.细胞色素 c 复合物的可能模型。有趣的是，该模型与细胞色素 b(5)-细胞色素 c 复合物的模型相似，其中细胞色素 c 结合到细胞色素 b(5) 暴露的血红素边缘周围的表面。因此，目前的结果支持血红素域迁移性是 Fcb2 功能的固有组成部分的观点。 (C) 2010 Elsevier Ltd. 保留所有权利。
Yeast flavocytochrome b(2) (Fcb2) is an L-lactate:cytochrome c oxidoreductase in the mitochondrial intermembrane space participating in cellular respiration. Each enzyme subunit consists of a cytochrome b(5)-like heme domain and a flavodehydrogenase (FDH) domain. In the Fcb2 crystal structure, the heme domain is mobile relative to the tetrameric FDH core in one out of two subunits. The monoclonal antibody B2B4, elicited against the holoenzyme, recognizes only the native heme domain in the holoenzyme. When bound, it suppresses the intramolecular electron transfer from flavin to heme b(2), hence cytochrome c reduction. We report here the crystal structure of the heme domain in complex with the Fab at 2.7 angstrom resolution. The Fab epitope on the heme domain includes the two exposed propionate groups of the heme, which are hidden in the interface between the domains in the complete subunit. The structure discloses an unexpected plasticity of Fcb2 in the neighborhood of the heme cavity, in which the heme has rotated. The epitope overlaps with the docking area of the FDH domain onto the heme domain, indicating that the antibody displaces the heme domain in a movement of large amplitude. We suggest that the binding sites on the heme domain of cytochrome c and of the FDH domain also overlap and therefore that cytochrome c binding also requires the heme domain to move away from the FDH domain, so as to allow electron transfer between the two hemes. Based on this hypothesis, we propose a possible model of the Fcb2.cytochrome c complex. Interestingly, this model shares similarity with that of the cytochrome b(5)-cytochrome c complex, in which cytochrome c binds to the surface around the exposed heme edge of cytochrome b(5). The present results therefore support the idea that the heme domain mobility is an inherent component of the Fcb2 functioning. (C) 2010 Elsevier Ltd. All rights reserved.