Einsle O, Mehrabian Z, Nalbandyan R, Messerschmidt A
Max-Planck-Institut für Biochemie, Abteilung Strukturforschung, Martinsried, Germany.
J Biol Inorg Chem. 2000 Oct;5(5):666-72. doi: 10.1007/s007750000154.
The crystal structure of the basic blue protein (plantacyanin) from spinach (SBP) has been solved to a resolution of 2.05 A by molecular replacement using the homologous protein from cucumber (CBP) as a model. Although the sequence identity of 58% between both proteins is only moderate, the three-dimensional structures turned out to be highly similar and the buried residues, which form the hydrophobic core of the protein, are almost completely conserved. However, the redox potentials of both proteins differ by 40 mV, and a comparison of the two structures leads to a single lysine replacing a proline in the cucumber sequence, which causes a shift of the peptide chain and thus a subtle distortion of the copper ligand geometry in respect to CBP. The crystal contained three monomers of SBP in the asymmetric unit which show considerable variations in outer loop regions owing to crystal packing, but not in the regions presumed to be essential for redox partner recognition and redox potential fine tuning of the copper centers. Still, bond length variations at the copper site are at the same scale between the monomers of SBP as they are in respect to CBP, indicating that in the oxidized state the protein does not impose a high conformational strain on the copper.
通过以黄瓜中的同源蛋白（CBP）为模型进行分子置换，已解析出菠菜中碱性蓝色蛋白（植蓝素，SBP）的晶体结构，分辨率达到2.05 Å。尽管两种蛋白之间58%的序列同一性仅为中等水平，但三维结构却高度相似，构成蛋白疏水核心的埋藏残基几乎完全保守。然而，两种蛋白的氧化还原电位相差40 mV，对这两种结构的比较发现，黄瓜序列中有一个赖氨酸取代了脯氨酸，这导致肽链发生位移，从而使铜配体几何结构相对于CBP产生细微扭曲。晶体的不对称单元中包含三个SBP单体，由于晶体堆积，它们在外环区域表现出相当大的差异，但在推测对氧化还原伙伴识别和铜中心氧化还原电位微调至关重要的区域则没有差异。尽管如此，SBP单体之间铜位点的键长变化与相对于CBP的键长变化处于同一尺度，这表明在氧化状态下，该蛋白不会对铜施加高构象应变。
