Crystallographic Study of a Quinoprotein Electron Transfer System: Methylamine Dehydrogenase

用X射线衍射法对脱氮副球藻藜麦蛋白-电子转移系统甲胺脱氢酶(MADH)进行了结构研究。该系统涉及MADH、氨基花青素和细胞色素C551I三种蛋白。MADH是一种124 kDa的二聚体，含有不寻常的辅因子色氨酸色氨酸对苯二酚。氨蓝蛋白是一种大小为12.5 kDa的蓝铜蛋白，能与MADH特异结合。细胞色素C551I是一种22 kDa的蛋白质，它接受来自氨蓝蛋白的电子，并通过另一种细胞色素将电子转移到末端的氧化酶。制备了MADH、氨基花青素、MADH与氨基花青素的二元络合物以及MADH、氨花青素和细胞色素C551I的三元络合物的晶体。MADH和二元络合物的结构通过分子置换分别得到了2.8A和2.5A的分辨率。剩下的晶体类型和细胞色素本身的结构将被确定。通过模拟退火法和能量最小化法对所有晶体类型的结构进行细化。将使用分子图形学仔细分析这些结构，以确定催化机理和电子转移过程的细节。

Structural studies will be carried out on the quinoprotein-electron transfer system methylamine dehydrogenase (MADH) from Paracoccus denitrificans by the methods of x-ray diffraction. Three proteins are involved in this system, MADH, amicyanin and cytochrome c551i. MADH is a dimer of 124 kDa and contains the unusual cofactor tryptophan tryptophylquinone. Amicyanin is a blue copper protein of 12.5 kDa which interacts specifically with MADH. Cytochrome c551i is a 22 kDa protein which accepts electrons from amicyanin and transfers them via another cytochrome to a terminal oxidase. Crystals have been prepared of MADH, amicyanin, the binary complex of MADH with amicyanin and of the ternary complex of MADH, amicyanin and cytochrome c551i. The structures of MADH and the binary complex have been solved by molecular replacement to 2.8 A and 2.5 A resolution, respectively. The structures of the remaining crystal types and of the cytochrome by itself will be determined. The structures of all crystal types will be refined by simulated annealing and energy minimization. These structures will be carefully analyzed using molecular graphics to determine the catalytic mechanisms and details of the electron transfer processes.