高分辨率高精度蛋白质晶体结构

自从六十年代初期应用X射线晶体衍射方法测定第一个蛋白质(肌红蛋白)的三维结构以来,我们关于蛋白质三维结构的知识已有了相当的积累.截止86年7月的统计,已有286个蛋白质分子的原子坐标存入国际蛋白质数据库.以此为基础,一些重要生命活动的结构机理已经在三维水平上得到精细阐明(参见),一个由分子生物学和X射线晶体学结合形成的新领域——蛋白质晶体学,应运而生.二十多年来,这一领域的发展已经历了二个阶段.第一阶段大体从六十年代初到七十年代中期,在这期间,分析方法和技术从突破发展到成熟和实用,并有近40个蛋白质结构测定出来,使我们获得了蛋白质结构知识的面面观.

REFINED CRYSTAL STRUCTURE OF PROTEIN AT HIGH RESOLUTION

It is a challenging problem in the protein crystallography to elucidate a pro-tien structure at the resolution higher than 1.5 A with the extensive refinement, through which the atomic co-ordinates of the molecule can accurately be determined. The refined structure at a very high resolution is significant not only for the study of fine stereochmistry of protein but also for the understanding of the structure-function relationship, the intercation between the protein molecule and its surrounding water molecules, and the conformational flexibility or mobility of the molecule. The high resolution crystals, the methods of the crystallographic refinement and the informations resulted from the refined structure are discussed with the practical experiences in this paper.As the excellent examples, the crystallographic refinement of insulin structu-re and des-pentapeptide insulin (DPI) structure at the resolutions 1.2A and 1.5 A respectively, carried out in the writer's lab, are described. The total of 131000 reflections of pig insulin crystals were collected in the range of 25-1.2A which were merged into 26135 uniqe reflections with Rmerge = 0.053. The reciprocal space least-squares method with the restraint of stereochemical parameters, packaged in the program system PROLSQ/PROTIN(Hendrickson and Konnert), was used in the refinements of both insulin and DPI. The final agreement factors (R) were 0.128 and 0.144 for insulin DPI respectively. In the refined model 2/3 content of water molecutes in an unit cell and 80% contant of hydrogen atoms of the insulin molecule were located. The anisotropic temperature factors of some atoms in the insulin cuold also be detected. Comparisons of the refined insulin model with the comparably refined DPI model revealed some interesting informations related to the structure-function relationship of insulin, e.g. the structure features of insulin monomer, the correlations between the activity change and co-formational changes of the B-chain residues on the binding surface, ect.