沉淀剂类型对蛋白质晶体分子堆积的影响

以不对称单位只有一个分子的牛胰核糖核酸酶和T4溶菌酶晶体为材料，着重研究了无机盐、有机溶剂和PEG三类不同的沉淀剂对晶体分子堆积的影响，经研究发现两种蛋白质中用无机盐做沉淀剂的晶型几乎都含有面积较大的二次轴对称接触面和较少的相邻分子数，同时其含有的参与接触的非极性残基集中分布于二次轴对称接触面，而盐键则在二次轴对称接触面上分布稀少。用有机溶剂作沉淀剂的晶型却含有面积较小的非二次轴对称接触面和较多的相含分子数，而参与接触的非极性残基和直键在各个非二次轴对称接触面上随机分布，用PEG作沉淀剂的晶型其分子堆积特征总体上类似于用有机溶剂作沉淀剂的晶型，但个别晶型具有与用无机盐做沉淀剂的晶型相似的分子堆积特征，以上结果提示，用三类沉淀剂得到的不同的分子堆积特征可能与三类沉淀剂不同的诱导结晶机理密切相关。

EFFECTS OF THE PRECIPITANT KINDS ON THE MOLECULAR PACKING OF PROTEIN CRYSTALS

The effects of three kinds of precipitants, i.e. salt, organic precipitant and PEG on the molecular packing are analyzed with 12 different crystal forms of T4 lysozyme and bovine pancreatic ribonuclease, where there is only one protein molecule in an asymmetric unit. Most of crystal forms grown in salt solution have large 2-fold symmetry interfaces, and have a small number of neighboring molecules and unique interfaces. And in the crystal forms grown in salt solution, compared to other in-terfaces, 2-fold symmetry interfaces have more non-polar residues that take part in molecular interaction and less salt bridges. All crystal forms grown in organic precipitant only have small non-2-fold symmetry interfaces, but have a large number of neighboring molecules and unique interfaces. And in these crystal forms, non-polar residues that take part in molecular interaction and salt bridges can be distributed ran-domly over all non-2-fold symmetry interfaces. The feature of molecular packing for most crystal forms grown in PEG is more like that of the crystal forms grown in organic precipitant. These results imply that the molecular packing might be closely related to the mechanism for different kinds of precitants to induce crystallization.