Heinemann U
Abteilung Saenger, Institut für Kristallographie, Freie Universität Berlin, FRG.
J Biomol Struct Dyn. 1991 Feb;8(4):801-11. doi: 10.1080/07391102.1991.10507846.
A simple relation exists between the packing density in crystals of short A-DNA duplexes and their global double-helical structure. The volume per nucleotide pair shows a linear inverse correlation with the mean displacement of base pairs from the best straight helix axis. The mean displacement is a measure of major groove depth and varies between -3.3 A and -4.9 A in A-form oligonucleotides analysed in the crystalline state. Since the mean displacement of base pairs from the helix axis determines other helical parameters such as base-pair longitudinal slide, its correlation with crystal packing is of considerable interest. The displacement-packing correlation is very clear for octamer duplexes which crystallize in three different lattices. Longer A-helical fragments sometimes deviate from the rule. It may be speculated whether A-form duplexes not completing a full helical turn are especially prone to distortions due to packing in crystals or arising from intermolecular contacts in solution.
短A-DNA双链体晶体中的堆积密度与其整体双螺旋结构之间存在一种简单的关系。每个核苷酸对的体积与碱基对相对于最佳直螺旋轴的平均位移呈线性反比关系。平均位移是大沟深度的一种度量，在晶体状态下分析的A-型寡核苷酸中，其值在-3.3埃至-4.9埃之间变化。由于碱基对相对于螺旋轴的平均位移决定了其他螺旋参数，如碱基对的纵向滑动，因此其与晶体堆积的相关性备受关注。对于在三种不同晶格中结晶的八聚体双链体，位移-堆积相关性非常明显。较长的A-螺旋片段有时会偏离该规律。可以推测，未完成完整螺旋圈的A-型双链体是否特别容易因晶体中的堆积或溶液中的分子间接触而产生扭曲。
