DETERMINATION AND ANALYSIS OF THE 2A STRUCTURE OF COPPER, ZINC SUPEROXIDE-DISMUTASE
DETERMINATION AND ANALYSIS OF THE 2A STRUCTURE OF COPPER, ZINC SUPEROXIDE-DISMUTASE
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DOI：
10.1016/0022-2836(82)90174-7
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发表时间：
1982-01-01
影响因子：
5.6
通讯作者：
RICHARDSON, DC
中科院分区：
文献类型：
--
作者：
TAINER, JA;GETZOFF, ED;RICHARDSON, DC
测定了牛红细胞Cu，Zn超氧化物歧化酶的结构为2.分辨率仅使用超过4埃的较大结构因子。该酶以空间群C2结晶，具有2个二聚酶分子/不对称单元。所有4个晶体学上独立的亚基分别拟合到2埃处的电子密度图。北卡罗来纳州[美国] GRIP-75分子图形系统的分辨率。使用Hendrickson和Konnert（1980）程序对原子坐标进行细化，以针对结构因子进行立体化学限制细化，这允许使用非晶体学对称性。精细模型的晶体学残余误差为25.5%，均方根偏差为0.03埃。从理想键长和12埃2的平均原子温度因子。每个酶亚基主要由8个反平行的β组成。形成扁平圆柱体的股，加上3个外部环。的β筒是不对称的，并且可以被视为具有2个不同的侧面; β。股线5-8比股线1-4更短且具有更少H键、更少的规则侧链交替和更大的扭曲。主链H键主要连接β。链残基;侧链到主链的H键广泛地参与紧转角的形成，紧转角形成3个环的主要结构元件。最大的环包括二硫键区和Zn配体区两者，其中每一个在总体结构上类似于另外2个环中的1个。第二大环包括α的短部分。螺旋。最小的环在β的1端形成希腊键连接。每桶形成左手螺旋的单个二硫键将最大的环共价连接到β的开始。8.对称相关β凸起对将2个大环向后折叠抵靠β的外表面。桶以包围活动通道。活性中心Cu（II）和Zn（II）位于6.3埃。在这个长通道的底部分开; Zn被掩埋，而Cu是溶剂可接近的。His 61的侧链在Cu和Zn之间形成桥，并且在数据的当前准确度内与它们共面。His 44的Cu配体ND 1和His 46、-61和-118的Cu配体NE 2显示出从正方形平面的不均匀四面体畸变。Cu具有暴露于溶剂的第5轴配位。His 61、-69和-78的Zn配体ND 1和Asp 81的OD 1显示四面体几何形状，具有朝向在顶点处具有掩埋Asp 81的三角锥的强烈变形。金属配体残基的侧链和主链都通过氢键的复杂网络稳定在其方向上。
The structure of bovine erythrocyte Cu,Zn superoxide dismutase was determined to 2 .ANG. resolution using only the larger structure factors beyond 4 .ANG.. The enzyme crystallizes in space group C2 with 2 dimeric enzyme molecules/asymmetric unit. All 4 crystallographically independent subunits were fitted separately to the electron density map at 2 .ANG. resolution on the University of North Carolina [USA] GRIP-75 molecular graphics system. Atomic coordinates were refined using the Hendrickson and Konnert (1980) program for stereochemically restrained refinement against structure factors, which allowed the use of noncrystallographic symmetry. The crystallographic residual error for the refined model was 25.5%, with a root-mean-square deviation of 0.03 .ANG. from ideal bond lenths and an average atomic temperature factor of 12 .ANG.2. Each enzyme subunit is composed primarily of 8 antiparallel .beta. strands that form a flattened cylinder, plus 3 external loops. The .beta. barrel is asymmetrical and can be viewed as having 2 distinct sides; .beta. strands 5-8 are shorter and have fewer H bonds, less regular side-chain alternation and greater twist than strands 1-4. The main-chain H bonds primarily link .beta. strand residues; side-chain to main-chain H bonds are extensively involved in the formation of tight turns, which form a major structural element of the 3 loops. The largest loop includes both a disulfide region and a Zn-liganding region, each of which resembles 1 of the other 2 loops in overall structure. The 2nd largest loop includes a short section of .alpha. helix. The smallest loop forms a Greek key connection across 1 end of the .beta. barrel. The single disulfide bond, which forms a left-handed spiral, covalently joins the largest loop to the beginning of .beta. strand 8. Symmetrically related .beta. bulge pairs fold the 2 large loops back against the external surface of the .beta. barrel to surround the active channel. The active site Cu(II) and Zn(II) lie 6.3 .ANG. apart at the bottom of this long channel; the Zn is buried, while the Cu is solvent-accessible. The side-chain of His61 forms a bridge between the Cu and Zn and is coplanar with them within the current accuracy of the data. The Cu ligands ND1 of His44 and NE2 of His46, -61 and -118 show an uneven tetrahedral distortion from a square plane. The Cu has a 5th axial coordination position exposed to solvent. Zn ligands ND1 of His61, -69 and -78 and OD1 of Asp81 show tetrahedral geometry with a strong distortion toward a trigonal pyramid having the buried Asp81 at the apex. Both the side-chains and main-chains of the metal-liganding residues are stabilized in their orientation by a complex network of H bonds.