Guss J M, Harrowell P R, Murata M, Norris V A, Freeman H C
J Mol Biol. 1986 Nov 20;192(2):361-87. doi: 10.1016/0022-2836(86)90371-2.
The structure of poplar plastocyanin in the reduced (CuI) state has been determined and refined, using counter data recorded from crystals at pH 3.8, 4.4, 5.1, 5.9, 7.0 and 7.8 (resolution 1.9 A, 1.9 A, 2.05 A, 1.7 A, 1.8 A and 2.15 A; the final residual R value was 0.15, 0.15, 0.16, 0.17, 0.16 and 0.15, respectively). The molecular and crystal structure of the protein is substantially the same in the reduced state as in the oxidized state. The refinements of the structures of the six forms of the reduced protein could therefore be commenced with a model derived from the known structure of CuII-plastocyanin. The refinements were made by reciprocal space least-squares calculations interspersed with inspections of electron-density difference maps. Precautions were taken to minimize any bias of the results of the refinements in the direction of the starting model. The most significant differences among the structures of the reduced protein at the six pH values, or between them and the structure of the oxidized protein, are concentrated at the Cu site. In the reduced protein at high pH (pH 7.8), the CuI atom is co-ordinated by the N delta(imidazole) atoms of His37 and His87, the S gamma(thiolate) atom of Cys84, and the S delta(thioether) atom of Met92, just as in CuII-plastocyanin. The distorted tetrahedral geometry and the unusually long Cu-S(Met92) bond are retained. The only effects of the change in oxidation state are a lengthening of the two Cu-N(His) bonds by about 0.1 A, and small changes in two bond angles involving the Cu-S(Cys) bond. The high-pH form of reduced plastocyanin accordingly meets all the requirements for efficient electron transfer. As the pH is lowered, the Cu atom and the four Cu-binding protein side-chains appear to undergo small but concerted movements in relation to the rest of the molecule. At low pH (pH 3.8), the CuI atom is trigonally co-ordinated by N delta(His37), S gamma(Cys84) and S delta(Met92). The fourth Cu-ligand bond is broken, the Cu atom making only a van der Waals' contact with the imidazole ring of His87. The trigonal geometry of the Cu atom strongly favours CuI, so that this form of the protein should be redox-inactive. This is known to be the case.(ABSTRACT TRUNCATED AT 400 WORDS)
已确定并精修了处于还原态（CuI）的杨树质体蓝素的结构，使用的是在pH 3.8、4.4、5.1、5.9、7.0和7.8条件下从晶体记录的计数器数据（分辨率分别为1.9 Å、1.9 Å、2.05 Å、1.7 Å、1.8 Å和2.15 Å；最终残余R值分别为0.15、0.15、0.16、0.17、0.16和0.15）。该蛋白质的分子结构和晶体结构在还原态与氧化态时基本相同。因此，还原态蛋白质六种形式的结构精修可以从源自CuII - 质体蓝素已知结构的模型开始。精修通过倒易空间最小二乘法计算，并穿插对电子密度差图的检查来进行。已采取预防措施，以使精修结果在起始模型方向上的任何偏差最小化。在六个pH值下还原态蛋白质的结构之间，或它们与氧化态蛋白质结构之间最显著的差异集中在铜位点。在高pH（pH 7.8）的还原态蛋白质中，CuI原子由His37和His87的Nδ（咪唑）原子、Cys84的Sγ（硫醇盐）原子以及Met92的Sδ（硫醚）原子配位，就如同在CuII - 质体蓝素中一样。扭曲的四面体几何结构和异常长的Cu - S（Met92）键得以保留。氧化态变化的唯一影响是两条Cu - N（His）键延长了约0.1 Å，以及涉及Cu - S（Cys）键 的两个键角有小的变化。因此，高pH形式的还原态质体蓝素满足高效电子转移的所有要求。随着pH降低，Cu原子和四个与铜结合的蛋白质侧链相对于分子的其余部分似乎经历了小而协同的移动。在低pH（pH 3.8）时，CuI原子由Nδ（His37）、Sγ（Cys84）和Sδ（Met92）呈三角配位。第四条与铜配位的键断裂，Cu原子仅与His87的咪唑环形成范德华接触。Cu原子的三角几何结构强烈有利于CuI，因此这种形式的蛋白质应该是氧化还原无活性的。已知情况确实如此。（摘要截于400字）
