CAS in Crystallography and Biophysics, University of Madras, Chennai 600 025, Tamil Nadu, India.
Biochem Biophys Res Commun. 2011 Apr 8;407(2):307-12. doi: 10.1016/j.bbrc.2011.03.007. Epub 2011 Mar 21.
We report the 2.6Å resolution crystal structure of the tetra-decamer d(CGCGGGTACCCGCG) in the tetragonal space group P4₃. This sequence contains the KpnI restriction site GGTACC in the centre which is flanked by alternating 'CG' sequences, and has a 'TA' step at the centre. These are features could favour the left-handed Z type helix. Despite this, overall the molecule has the A form. This is the first tetra-decamer crystallized in the A-DNA conformation, i.e. more than one full turn of the A helix. The crystallographic asymmetric unit consists of one tetra-decamer duplex. The helical twist and slide, as well as the base pair-base pair stacking interactions show alternations at the alternating pyrimidine-purine and purine-pyrimidine base steps. This variation is reminiscent of the dinucleotide repeat in left-handed Z-DNA helices. The crystal packing is unlike other A-DNA crystal structures, with each helix having a large number of contacts of many different types with symmetry-related neighbours.
我们报告了四聚体 d(CGCGGGTACCCGCG)在四面体型 P4₃空间群中的 2.6Å 分辨率晶体结构。该序列在中心包含 KpnI 限制位点 GGTACC，其两侧为交替的“CG”序列，并且在中心有一个“TA”步。这些特征可能有利于左手 Z 型螺旋。尽管如此，分子总体上仍呈 A 型。这是第一个以 A-DNA 构象结晶的四聚体，即 A 螺旋的完整转角超过一次。晶体学不对称单位由一个四聚体双链体组成。螺旋扭曲和滑动以及碱基对-碱基对堆积相互作用在交替的嘧啶-嘌呤和嘌呤-嘧啶碱基步中表现出交替。这种变化让人联想到左手 Z-DNA 螺旋中的二核苷酸重复。晶体堆积与其他 A-DNA 晶体结构不同，每个螺旋与对称相关的相邻体具有大量不同类型的接触。
