Schirmer T, Bode W, Huber R, Sidler W, Zuber H
J Mol Biol. 1985 Jul 20;184(2):257-77. doi: 10.1016/0022-2836(85)90379-1.
The structure of the biliprotein C-phycocyanin from the thermophilic cyanobacterium Mastigocladus laminosus has been determined at 3 A resolution by X-ray diffraction methods. Phases have been obtained by the multiple isomorphous replacement method. The electron density map could be improved by solvent flattening and has been interpreted in terms of the amino acid sequence. The protein consists of three identical (alpha-beta)-units which are arranged around a threefold symmetry axis to form a disc of approximate dimensions 110 A X 30 A with a central channel of 35 A in diameter. This aggregation form is supposed to be the same as that found in the rods of native phycobilisomes. Both subunits, alpha and beta, exhibit a similar structure and are related by a local twofold rotational axis. Each subunit is folded into eight helices and irregular loops. Six helices are arranged to form a globular part, whereas two helices stick out and mediate extensive contact between the subunits. The arrangement of the helices of the globular part resembles the globin fold: 59 equivalent C alpha-atoms have a root-mean-square deviation of 2 X 9 A. The chromophores attached to cystein 84 of the alpha- and beta-subunits are topologically equivalent to the haem. All three chromophores of C-phycocyanin, open-chain tetrapyrroles, are in an extended conformation. alpha 84 and beta 84 are attached to helix E (globin nomenclature), beta 155 is linked to the G--H loop. The shortest centre-to-centre distance between chromophores in trimer is 22 A.
通过X射线衍射方法,已在3埃分辨率下测定了嗜热蓝细菌层理鞭枝藻中胆蛋白C-藻蓝蛋白的结构。采用多重同晶置换法获得了相位。通过溶剂平整可改善电子密度图,并已根据氨基酸序列进行了解释。该蛋白质由三个相同的(α-β)单元组成,这些单元围绕三重对称轴排列,形成一个直径约为110埃×30埃的圆盘,中心通道直径为35埃。这种聚集形式被认为与天然藻胆体杆状结构中的形式相同。α和β两个亚基都呈现出相似的结构,并通过局部二重旋转轴相关联。每个亚基都折叠成八个螺旋和不规则环。六个螺旋排列形成一个球状部分,而两个螺旋伸出并介导亚基之间的广泛接触。球状部分螺旋的排列类似于珠蛋白折叠:59个等效的Cα原子的均方根偏差为2×9埃。与α和β亚基的半胱氨酸84相连的发色团在拓扑结构上与血红素等效。C-藻蓝蛋白的所有三个发色团,即开链四吡咯,均处于伸展构象。α84和β84连接到螺旋E(珠蛋白命名法),β155连接到G-H环。三聚体中发色团之间最短的中心距为22埃。