Romero A, De la Cerda B, Varela P F, Navarro J A, Hervás M, De la Rosa M A
Centro de Investigaciones Biológicas, CSIC, Madrid, Spain.
J Mol Biol. 1998 Jan 16;275(2):327-36. doi: 10.1006/jmbi.1997.1455.
The crystal structure of the triple mutant A42D/D47P/A63L plastocyanin from the cyanobacterium Synechocystis sp. PCC 6803 has been determined by Patterson search methods using the known structure of the poplar protein. Crystals of the triple mutant A42D/D47P/A63L, which are stable for days in its oxidized form, were grown from ammonium sulfate, with the cell constants a = b = 34.3 A and c = 111.8 A belonging to space group P3(2)21. The structure was refined using restrained crystallographic refinement to an R-factor of 16.7% for 4070 independent reflections between 8.0 and 2.15 A with intensities greater than 2 sigma (I), with root mean square deviations of 0.013 A and 1.63 degrees from ideal bond lengths and bond angles, respectively. The final model comprises 727 non-hydrogen protein atoms within 98 residues, 75 water molecules and a single copper ion. The overall tertiary fold of Synechocystis plastocyanin consists of a compact ellipsoidal beta-sandwich structure made up of two beta-sheets embracing a hydrophobic core. Each sheet contains parallel and antiparallel beta-strands. In addition to the beta-sheets, the structure contains an alpha-helix from Pro47 to Lys54 that follows beta-strand 4. The three-dimensional structure of Synechocystis plastocyanin is thus similar to those reported for the copper protein isolated from eukaryotic organisms and, in particular, from the cyanobacterium Anabaena variabilis, the only cyanobacterial plastocyanin structure available so far. The molecule holds an hydrophobic region surrounding His87, as do other plastocyanins, but the lack of negatively charged residues at the putative distant remote site surrounding Tyr83 could explain why the Synechocystis protein exhibits a collisional reaction mechanism for electron transfer to photosystem I (PSI), which involves no formation of the transient plastocyanin-PSI complex kinetically observed in green algae and higher plants.
利用杨树蛋白的已知结构，通过帕特森搜索法确定了来自集胞藻属PCC 6803蓝细菌的三重突变体A42D/D47P/A63L质体蓝素的晶体结构。三重突变体A42D/D47P/A63L的晶体在氧化形式下可稳定存在数天，其晶体由硫酸铵生长而成，晶胞常数a = b = 34.3 Å，c = 111.8 Å，属于空间群P3(2)21。使用约束晶体学精修对结构进行精修，对于8.0至2.15 Å之间、强度大于2σ（I）的4070个独立反射，R因子为16.7%，与理想键长和键角的均方根偏差分别为0.013 Å和1.63°。最终模型包含98个残基内的727个非氢蛋白原子、75个水分子和一个铜离子。集胞藻质体蓝素的整体三级结构由一个紧密的椭圆形β-折叠结构组成，该结构由两个β-折叠片围绕一个疏水核心构成。每个折叠片包含平行和反平行的β-链。除了β-折叠片外，该结构还包含从Pro47到Lys54的α-螺旋，该螺旋紧跟β-链4。因此，集胞藻质体蓝素的三维结构与从真核生物中分离得到的铜蛋白，特别是与迄今唯一可用的蓝细菌质体蓝素结构——多变鱼腥藻的铜蛋白结构相似。该分子与其他质体蓝素一样，在His87周围有一个疏水区域，但在Tyr83周围假定的远距离位点缺乏带负电荷的残基，这可以解释为什么集胞藻蛋白表现出一种碰撞反应机制，用于将电子转移到光系统I（PSI），该机制不涉及在绿藻和高等植物中动力学观察到的瞬时质体蓝素-PSI复合物的形成。
