T4溶菌酶晶体分子堆积的研究

MOLECULAR PACKING STUDY OF DIFFERENT CRYSTALFORMS OF T4 LYSOZYME

以不对称单位中只有一个分子的10种不同晶型的T4溶菌酶晶体为材料 ,对晶体中的分子堆积进行了研究。结果表明 ,在溶剂含量较高的晶型中 ,非极性基团在接触面积中所占的比例略高于溶剂含量较低的晶型 ,而其极性和带电荷基团在接触面积中所占的比例略低于溶剂含量较低的晶型。溶剂含量较高的晶型多含有晶体学二重轴 ,二重轴相关的分子间的接触与其他接触相比 ,含有较少的极性相互作用。这些结果说明溶剂含量的高低可能是由不同结晶环境引起的不同分子间的相互作用决定的。另外 ,研究进一步证实了分子堆积的非特异性 ,即不存在特异性的接触。研究还表明某些溶剂可及表面积较大的极性或带电荷的残基对分子堆积较为重要 ,常在不同的晶型中参与接触。

The molecular packing was analyzed with 10 different crystal forms of T4 lysozyme, where there is only one protein molecule in an asymmetric unit. The proportion of non-polar atoms involved in all interface areas in the crystal forms with higher solvent content is larger than that in the crystal forms with lower solvent content; the proportion of polar or charged atoms involved in all interface areas in the crystal forms with higher solvent content is less than that in the crystal forms with lower solvent content. Most crystal forms with higher solvent content contain 2-fold symmetry axes, which are rare in the crystal forms with lower solvent content. Compared to other contacts, contacts between 2-fold axis-related molecules contain less polar interactions. These results imply that the solvent content might be affected by different intermolecular interactions caused by different crystallization environments. In addition, no specific contacts were found in the molecular packing of T4 lysozyme crystals, and this confirms that the crystal packing is essentially non-specific. However, it has been reveaved that some polar or charged residues which have larger accessible surface areas, are of importantce for crystal packing, and these important residues may often present in intermolecular contacts in different crystal forms.