AN X-RAY ANALYSIS OF THE ORTHORHOMBIC CRYSTAL FORM OF TRICHOSANTHIN AT 5

Trichosanthin crystals grown at pH 5.4 are orthorhombic P2_12_12_1 with cell dimension α=38.23, b=76.18 and c=79.12. Each asymmetric unit contains one protein molecule of 234 amino acid residues (M. W. 26,000). The structure has been solved at 5 resolution by conventional MIR method with two heavy-atom derivatives. The preliminary result suggests that the protein molecule in acidic solution does not have dramatic conformational change, compared with that in alkali solution.     

激光光散射研究天花粉蛋白的聚集过程

运用激光光散射技术研究天花粉蛋白在水溶液及不同浓度KSCN水溶液中的聚集过程．KSCN的加入能提高天花粉在水溶液中的稳定性. KSCN浓度大于0．5mol•L－1时，天花粉溶液透明、稳定，溶液中天花粉以单个分子与聚集体两种形式存在．聚集体主要是由约120个天花粉分子组成，平均流体力学半径Rh值约为49nm，在溶液中排列疏松，类似θ溶剂中的无规线团。     

天花粉蛋白分子的三维结构

本文报道了我们最近建立的单斜晶胞内一个不对称单元中两个天花粉蛋白分子的模型,指出蛋白分子结构可以划分为大小两个结构域以及二级结构的一些特点,描述了独立单元中以一种非对称方式相关联的两个蛋白分子的差异及其相互作用,并解释了重原子衍生物的结合位置。     

1.73分辨率天花粉蛋白晶体中的水结构

本文报道的天花粉蛋白晶体中水的结构模型,包括了133个水分子,其中118个同蛋白的原子成氢键。天花粉蛋白内部有4个分立的水分子,其中2个水分子W251和W252分剔与A5螺旋变形部位的残基156Gln和157Ser的侧链成氢键,对维持活性部位的构象有贡献。晶体中水结构的比较结果表明,核糖体接近蛋白时,会诱导蛋白活性部位残基的构象发生变化,使各催化基团按催化效果最佳的构象排布,并激活一个水分子(W257)直接参与核糖体失活作用。     

A DETERMINATION OF THE THREE-DIMENSIONAL STRUCTURE OF TRICHOSANTHIN AT LOW RESOLUTION

Trichosanthin, extracted from a Chinese herb medicine, is a plant protein having a molec-ular weight of ca. 24,000 and containing 219 amino acid residues. The crystal is mono-clinic, belonging to the space group C2, with the following cell dimensions: a=75.64A, b=75.52A, c=88.85A β= 99.51°. Each asymmetric unit contains two such protein molecules. The UO_2Ac_2 and K_2Pt(NO_2)_4 derivatives of trichosanthin have been prepared by soakingin the respective solutions of high dilution. The joint probability of isomorphous replacementand anomalous scattering has been used to calculate the native phases. In the electron densitymaps, the boundary between the two protein molecules can be recognized, leading to thefollowing approximate molecular dimensions: 45×40×35A~3. Each molecule contains fourrod-shaped segments easily known as α-helices.     

THE COURSE OF THE POLYPEPTIDE CHAIN OF TRICHOSANTHIN MOLECULE

The course of the polypeptide chain of Trichosanthin has been determined from the electron density map at 4 resolution. The structure belongs to α+β type. It contains eight α-helices (39% of total residues) and four β-sheets (32% of total residues) which are made up of thirteen β-strands. The α-helices are relatively in the centre of the molecule and surrounded by β-sheets. This is the characteristic feature of Trichosanthin structure. This kind of structural arrangement has not been reported before. The transformation matrix and translation vector, which superpose two molecules in one asymmetric unit, were obtained. The root mean square error is 1.31 for this superposition.     

19-O-β-D-吡喃葡萄糖基脱氧穿心莲内酯的晶体结构

19—O-β-D-吡喃葡萄糖基脱氧穿心莲内酯是从中草药爵床科须药草属穿心莲植物中分离而得的一种甙类化合物,具有抗菌、消炎、解毒等性能本文测定其晶体结构,证明葡萄糖以β-甙键的形式与脱氧穿心莲内酯的C_(19)羟基连接.单晶由南京药学院提供.     

天花粉蛋白低分辨率晶体结构的测定

本文测出:天花粉蛋白分子量为24000,有219个氨基酸残基。晶体属单斜晶系,空间群为C2,晶胞参数a=75.64埃,b=75.52埃,c=88.85埃,β=99.51°,每个不对称单元内含2个分子。 用UO_2Ac_2和K_2Pt(NO_2)_4浸泡获得两个重原子衍生物,按照多对同晶置换加反常散射的联合概率法求得母体相角,计算了5埃和4埃分辨率电子密度图,从图上分辨出两个独立分子的界面,分子大小约为45×40×35埃~3,每个分子中有4段棒状的电子密度更为清晰,可辨认为α-螺旋结构。     

天花粉蛋白1.73分辨率结构测定及其精化

本文报道了用面探测器收集一套1.73分辨率天花粉蛋白(TCS)正交晶体的X射线衍射数据,利用已知的α苦瓜子蛋白模型,取10—4范围的TCS强度数据,应用分子置换法测定了晶体结构,并且采用限制参数最小二乘法在10—1.73分辨率范围内修正模型结构。修正结果,晶体学R因子为0.186,键长标准偏差为0.013,键角标准偏差为2.48°,一个不对称单位中找到133个水分子。本文详细描述了天花粉蛋白分子的结构、温度因子、氢键、结合水、保守残基的分布以及分子间相互作用。保守残基14Tyr的羟基与157位的羰基氧形成的氢键,对维持活性部位构象有重要作用;保守残基160Glu和它在活性部位的构象对酶的催化活性起着关键性作用。