Parker M W, Blake C C
Laboratory of Molecular Biophysics, University of Oxford, England.
J Mol Biol. 1988 Feb 20;199(4):649-61. doi: 10.1016/0022-2836(88)90308-7.
The crystal structure of manganese superoxide dismutase (MnSOD) from Bacillus stearothermophilus has been solved at 2.4 A resolution by a combination of multiple isomorphous replacement and molecular replacement (1 A = 0.1 nm). The structure has been refined to a conventional R-factor for all 16,560 unique reflections at 2.4 A of 0.26, and the 2Fo-Fc density maps show features more consistent with the known amino acid sequence of MnSOD from B. stearothermophilus than with the starting model, the MnSOD from Thermus thermophilus. The molecule is a dimer of identical subunits, each with 203 amino acid residues. The polypeptide chain of the monomer is organized into two domains, one of which has an "all-alpha" structure and the other an "alpha/beta" structure, with the manganese ion bound between them. The ion is co-ordinated by three histidine residues, 26, 81 and 167, and one aspartic acid residue, 173, in a tetrahedral arrangement strongly distorted towards trigonal pyramidal. We anticipate that Tyr34, whose hydroxyl group is only 5 A from the metal, is involved in the catalytic reaction. The active site is particularly rich in aromatic amino acid residues. As in the Cu/ZnSOD there are indications that MnSOD provides electrostatic guidance to the substrate entering the active site.
嗜热脂肪芽孢杆菌锰超氧化物歧化酶（MnSOD）的晶体结构通过多同晶置换和分子置换相结合的方法，在2.4埃分辨率下得以解析（1埃 = 0.1纳米）。该结构已针对2.4埃处的所有16,560个独立反射精修至传统R因子为0.26，并且2Fo - Fc电子密度图显示的特征与嗜热脂肪芽孢杆菌MnSOD已知氨基酸序列的一致性比与起始模型嗜热栖热菌的MnSOD更高。该分子是由相同亚基组成的二聚体，每个亚基有203个氨基酸残基。单体的多肽链被组织成两个结构域，其中一个具有“全α”结构，另一个具有“α/β”结构，锰离子结合在它们之间。该离子由三个组氨酸残基（26、81和167）和一个天冬氨酸残基（173）以四面体排列配位，该排列向三角锥严重扭曲。我们预计，羟基距金属仅5埃的Tyr34参与催化反应。活性位点特别富含芳香族氨基酸残基。与铜锌超氧化物歧化酶（Cu/ZnSOD）一样，有迹象表明MnSOD为进入活性位点的底物提供静电引导。
