Chantalat L, Wood S D, Rizkallah P, Reynolds C D
Biophysics Department, School of Biomolecular Sciences, Liverpool John Moores University, England.
Acta Crystallogr D Biol Crystallogr. 1996 Nov 1;52(Pt 6):1146-52. doi: 10.1107/S090744499600546X.
It is often the case that analogous proteins from different species crystallize in a different form. These structures can usually be easily solved by the molecular-replacement (MR) technique, as the protein folding is very often conserved. However, the results from MR become more uncertain as the proportion of diffracting matter decreases as a result of multimericity and/or absence of some of the atoms in the model. In this paper results are presented on the structure solution of amaryllis lectin (109 residues per monomer) containing two protein molecules in the asymmetric unit. The structure was solved by MR using the Calpha coordinates of one monomer from snowdrop lectin which has 85% amino-acid sequence identity to amaryllis lectin. This represents only 6% of the non-H atoms of the protein molecule to be used for structure determination and it is a major improvement on previous reports. Further calculations were carried out in order to establish the minimum number of atoms which could be included in the model before a clear solution to the MR problem was revealed. This study showed that the structure of amaryllis lectin could still have been solved easily with 3.85% of the model, which even in the most favourable cases, will probably constitute a minimum for molecular-replacement structure solution.
不同物种的类似蛋白质常常以不同的形式结晶。这些结构通常可以通过分子置换（MR）技术轻松解析，因为蛋白质折叠往往是保守的。然而，由于多聚体形成和/或模型中某些原子的缺失导致衍射物质比例降低，MR的结果变得更不确定。本文展示了关于包含两个蛋白质分子的孤挺花凝集素（每个单体109个残基）在不对称单元中的结构解析结果。该结构通过MR使用来自雪花莲凝集素的一个单体的α碳原子坐标解析，雪花莲凝集素与孤挺花凝集素具有85%的氨基酸序列同一性。这仅占用于结构测定的蛋白质分子非氢原子的6%，并且是对先前报告的重大改进。为了确定在揭示MR问题的清晰解决方案之前模型中可以包含的最少原子数，进行了进一步的计算。这项研究表明，即使在最有利的情况下，仅用模型的3.85%仍然可以轻松解析孤挺花凝集素的结构，这可能构成分子置换结构解析的最小值。
