The structural origin of nonplanar heme distortions in tetraheme ferricytochromes c3
The structural origin of nonplanar heme distortions in tetraheme ferricytochromes c3
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DOI：
10.1021/bi981189i
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发表时间：
1998-09-08
期刊：
影响因子：
2.9
通讯作者：
Shelnutt, JA
中科院分区：
文献类型：
--
作者：
Ma, JG;Zhang, J;Shelnutt, JA
用共振拉曼光谱(RR)、分子力学(MM)计算和法向配位结构分解(NSD)研究了铁细胞色素c(3)中铁血红素的构象差异。从X射线结晶学和细胞色素c(3)的血红素肽片段的MM计算获得的血红素结构的NSD分析表明，血红素的非平面性在很大程度上是由两个血红素连接的半胱氨酸、半胱氨酸之间的氨基酸和近端组氨酸配体组成的指纹肽片段控制的。血红素和远端之间的其他相互作用。组氨酸配基和亚铁血红素丙酸酯与蛋白质之间对亚铁血红素构象也有影响，但影响程度小于指纹肽片段。此外，影响指纹肽片段折叠模式的因素可能会对血红素的构象产生影响。NSD程序发现杆状杆菌细胞色素cs和其他蛋白质之间存在巨大的血红素结构差异[Jentzen，W.，Ma，J.-G.和Shelnutt，J.A.(1998)BiPhys.J.74,753-763]。这些差异主要与血红素4的共价连接片段中杆状蛋白的两个残基缺失有关。此外，这些结构差异中的一些反映在RR谱中。例如，在RR光谱的高频区，结构敏感线(nu(4)、nu(3)和nu(2))的频率对杆状脱硫菌a(挪威4和9974)比对脱硫菌弧菌(D)低。吉卡斯、普通杜氏菌和脱硫杜氏菌菌株，与更具褶皱的亚铁血红素相一致。对Nu(3)和Nu(10)谱线的光谱分解允许将亚线分配给单个的血红素，并表明褶皱而不是鞍状是影响结构敏感拉曼线频率的主要因素。所研究的杆状杆菌菌株的独特光谱是由于血红素2和4比典型的其他蛋白质更具褶皱。
Resonance Raman (RR) spectroscopy, molecular mechanics (MM) calculations, and normal-coordinate structural decomposition (NSD) have been used to investigate the conformational differences in the hemes in ferricytochromes c(3). NSD analyses of heme structures obtained from X-ray crystallography and MM calculations of heme-peptide fragments of the cytochromes c(3) indicate that the nonplanarity of the hemes is largely controlled by a fingerprint peptide segment consisting of two heme-linked cysteines, the amino acids between the cysteines, and the proximal histidine ligand. Additional interactions between the heme and the distal. histidine ligand and between the heme propionates and the protein also influence the heme conformation, but to a lesser extent than the fingerprint peptide segment. In addition, factors that influence the folding pattern of the fingerprint peptide segment may have an effect on the heme conformation. Large heme structural differences between the baculatum cytochromes cs and the other proteins are uncovered by the NSD procedure [Jentzen, W., Ma, J.-G., and Shelnutt, J. A. (1998) Biophys. J. 74, 753-763]. These heme differences are mainly associated with the deletion of two residues in the covalently linked segment of hemes 4 for the baculatum proteins. Furthermore, some of these structural differences are reflected in the RR spectra. For example, the frequencies of the structure-sensitive lines (nu(4), nu(3), and nu(2)) in the high-frequency region of the RR spectra are lower for the Desulfomicrobium baculatum cytochromes a (Norway 4 and 9974) than for the Desulfovibrio (D.) gigas, D. vulgaris, and D. desulfuricans strains, consistent with a more ruffled heme. Spectral decompositions of the nu(3) and nu(10) Lines allow the assignment of the sublines to individual hemes and show that ruffling, not saddling, is the dominant factor influencing the frequencies of the structure-sensitive Raman lines. The distinctive spectra of the baculatum strains investigated are a consequence of hemes 2 and 4 being more ruffled than is typical of the other proteins.