EFFECTS OF THE PRECIPITANT KINDS ON THE MOLECULAR PACKING OF PROTEIN CRYSTALS
沉淀剂类型对蛋白质晶体分子堆积的影响

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.