Collyer C A, Guss J M, Sugimura Y, Yoshizaki F, Freeman H C
Department of Inorganic Chemistry, University of Sydney, Australia.
J Mol Biol. 1990 Feb 5;211(3):617-32. doi: 10.1016/0022-2836(90)90269-R.
The crystal structure of the Cu-containing protein plastocyanin (Mr 10,500) from the green alga Enteromorpha prolifera has been solved by molecular replacement. The structure was refined by constrained-restrained and restrained reciprocal space least-squares techniques. The refined model includes 111 solvent sites. There is evidence for alternate conformers at eight residues. The residual is 0.12 for a data set comprising 74% of all observations accessible at 1.85 A resolution. The beta-sandwich structure of the algal plastocyanin is effectively the same as that of poplar leaf (Populus nigra var. italica) plastocyanin determined at 1.6 A resolution. The sequence homology between the two proteins is 56%. Differences between the contacts in the hydrophobic core create some significant (0.5 to 1.2 A) movements of the polypeptide backbone, resulting in small differences between the orientations and separations of corresponding beta-strands. These differences are most pronounced at the end of the molecule remote from the Cu site. The largest structural differences occur in the single non-beta strand, which includes the sole turn of helix in the molecule: two of the residues in a prominent kink of the poplar plastocyanin backbone are missing from the algal plastocyanin sequence, and there is a significant change in the position of the helical segment in relation to the beta-sandwich. Several other small but significant structural differences can be correlated with intermolecular contacts in the crystals. An intramolecular carboxyl-carboxylate hydrogen bond in the algal plastocyanin may be associated with an unusually high pKa. The dimensions of the Cu site in the two plastocyanins are, within the limits of precision, identical.
通过分子置换法解析了来自绿藻浒苔的含铜蛋白质体蓝素（分子量10,500）的晶体结构。采用约束-约束和约束倒易空间最小二乘法对结构进行了优化。优化后的模型包含111个溶剂位点。有证据表明在8个残基处存在交替构象。对于在1.85埃分辨率下可获得的所有观测数据的74%组成的数据集，残差为0.12。藻类质体蓝素的β-三明治结构与在1.6埃分辨率下测定的杨树叶（黑杨意大利变种）质体蓝素的结构基本相同。这两种蛋白质之间的序列同源性为56%。疏水核心中接触的差异导致多肽主链出现一些显著（0.5至1.2埃）的移动，从而使相应β链的方向和间距存在微小差异。这些差异在远离铜位点的分子末端最为明显。最大的结构差异出现在单一的非β链中，该链包含分子中唯一的螺旋转角：藻类质体蓝素序列中缺少杨树叶质体蓝素主链一个明显扭结处的两个残基，并且螺旋段相对于β-三明治的位置发生了显著变化。其他几个小但显著的结构差异可能与晶体中的分子间接触有关。藻类质体蓝素中的分子内羧基-羧酸盐氢键可能与异常高的pKa有关。两种质体蓝素中铜位点的尺寸在精度范围内是相同的。
