Svensson B, Vass I, Cedergren E, Styring S
Department of Biochemistry, University of Stockholm, Sweden.
EMBO J. 1990 Jul;9(7):2051-9. doi: 10.1002/j.1460-2075.1990.tb07372.x.
Thirty-one and eleven sequences for the photosystem II reaction centre proteins D1 and D2 respectively, were compared to identify conserved single amino acid residues and regions in the sequences. Both proteins are highly conserved. One important difference is that the lumenal parts of the D1 protein are more conserved than the corresponding parts in the D2 protein. The three-dimensional structures around the electron donors tyrosineZ and tyrosineD on the oxidizing side of photosystem II have been predicted by computer modelling using the photosynthetic reaction centre from purple bacteria as a framework. In the model the tyrosines occupy two cavities close to the lumenal surface of the membrane. They are symmetrically arranged around the primary donor P680 and the distances between the centre of the tyrosines and the closest Mg ion in P680 are around 14 A. Both tyrosineZ and tyrosineD are suggested to form a hydrogen bond with histidine 190 from the loop connecting helices C and D in the D1 and D2 proteins, respectively. The Mn cluster in the oxygen evolving complex has been localized by using known and estimated distances from the tyrosine radicals. It is suggested that a binding region for the Mn cluster is constituted by the lumenal ends of helices A and B and the loop connecting them in the D1 protein. This part of the D1 protein contains a large number of strictly conserved carboxylic acid residues and histidines which could participate in the Mn binding. There is little probability that the Mn cluster binds on the lumenal surface of the D2 protein.
分别对光系统II反应中心蛋白D1和D2的31个和11个序列进行了比较，以确定序列中保守的单个氨基酸残基和区域。这两种蛋白质都高度保守。一个重要的区别是，D1蛋白的腔内部份比D2蛋白的相应部份更保守。利用紫色细菌的光合反应中心作为框架，通过计算机建模预测了光系统II氧化侧电子供体酪氨酸Z和酪氨酸D周围的三维结构。在该模型中，酪氨酸占据靠近膜腔表面的两个腔。它们围绕初级供体P680对称排列，酪氨酸中心与P680中最接近的镁离子之间的距离约为14埃。酪氨酸Z和酪氨酸D分别被认为与D1和D2蛋白中连接螺旋C和D的环中的组氨酸190形成氢键。通过使用与酪氨酸自由基的已知距离和估计距离，对放氧复合体中的锰簇进行了定位。有人提出，锰簇的结合区域由D1蛋白中螺旋A和B的腔端以及连接它们的环构成。D1蛋白的这一部分含有大量严格保守的羧酸残基和组氨酸，它们可能参与锰的结合。锰簇结合在D2蛋白腔表面的可能性很小。
