Ficner R, Lobeck K, Schmidt G, Huber R
Max-Planck-Institut für Biochemie, Martinsried, Germany.
J Mol Biol. 1992 Dec 5;228(3):935-50. doi: 10.1016/0022-2836(92)90876-l.
The light-harvesting pigment-protein complex B-phycoerythrin from the red alga Porphyridium sordidum has been isolated and crystallized. B-Phycoerythrin consists of three different subunits forming an (alpha beta)6 gamma aggregate. The three-dimensional structure of the (alpha beta)6 hexamer was solved by Patterson search techniques using the molecular model of C-phycocyanin from Fremyella diplosiphon. The asymmetric unit of the crystal cell (space group P3, with a = b = 111.2 A, c = 59.9 A, alpha = beta = 90 degrees, gamma = 120 degrees) contains two (alpha beta) monomers related by a local dyad. Three asymmetric units are arranged around the crystallographic 3-fold axis building an (alpha beta)6 hexamer, as in C-phycocyanin. The crystal structure has been refined by energy-restrained crystallographic refinement and model building. The conventional R-factor of the final model was 18.9% with data to 2.2 A resolution. The molecular structures of the alpha and beta-subunits resemble those of C-phycocyanin. Major changes in comparison to phycocyanin are caused by deletion or insertion of segments involved in protein-chromophore interactions. The singly linked phycoerythrobilin chromophores alpha-84, alpha-140a, beta-84 and beta-155 are each covalently bound to a cysteine by ring A. The doubly linked chromophore beta-50/beta-61 is attached at cysteine beta-50 through ring A and at cysteine beta-61 through ring D. B-Phycoerythrin contains additionally a 30 kDa gamma-subunit, which is presumably located in the central cavity of the hexamer. It is disordered, as a consequence of crystal and local symmetry averaging.
已从紫球藻中分离并结晶出捕光色素蛋白复合物B-藻红蛋白。B-藻红蛋白由三个不同的亚基组成，形成一个(αβ)6γ聚集体。利用来自双歧藻的C-藻蓝蛋白分子模型，通过帕特森搜索技术解析了(αβ)6六聚体的三维结构。晶胞的不对称单元（空间群P3，a = b = 111.2 Å，c = 59.9 Å，α = β = 90°，γ = 120°）包含两个通过局部二元轴相关的(αβ)单体。与C-藻蓝蛋白一样，三个不对称单元围绕晶体学3重轴排列，形成一个(αβ)6六聚体。通过能量约束晶体学精修和模型构建对晶体结构进行了精修。最终模型的传统R因子为18.9%，数据分辨率为2.2 Å。α和β亚基的分子结构与C-藻蓝蛋白相似。与藻蓝蛋白相比，主要变化是由参与蛋白质-发色团相互作用的片段的缺失或插入引起的。单连接的藻红胆素发色团α-84、α-140a、β-84和β-155各自通过A环与半胱氨酸共价结合。双连接的发色团β-50/β-61通过A环连接在半胱氨酸β-50上，通过D环连接在半胱氨酸β-61上。B-藻红蛋白还含有一个30 kDa的γ亚基，推测位于六聚体的中央腔中。由于晶体和局部对称性平均，它是无序的。
