Weil J, Min T, Yang C, Wang S, Sutherland C, Sinha N, Kang C
Department of Biochemistry and Biophysics, Washington State University, Pullman, WA 99164-4660, USA.
Acta Crystallogr D Biol Crystallogr. 1999 Feb;55(Pt 2):422-9. doi: 10.1107/s0907444998012529.
The crystal structure of d(ACCCT), solved by molecular replacement, shows a four-stranded i-motif conformation, where two parallel duplexes intercalate with one another in opposite orientations. Each duplex is stabilized by hemi-protonated C-C+ base pairing between parallel strands, and a string of water molecules bridge the cytosine N4 atoms to phosphate O atoms. This structure of d(ACCCT) shows examples of reversed Hoogsteen and Watson-Crick base pairing in both intermolecular and intramolecular manners to stabilize the tetraplex. Noticeably, the four-stranded complex is further stabilized at one end by a three-base hydrogen-bonding network, in which two adenines and a thymine form four hydrogen bonds via a reverse Hoogsteen and an asymmetric adenine-adenine base pairing. The structure of d(ACCCT) shows a similar local structure to that found in the d(TAA) part of the crystal structure of d(TAACCC) and provides further structural evidence that these base arrangements are essential for stabilizing these novel DNA super-secondary structures.
通过分子置换解析得到的d(ACCCT)晶体结构显示出一种四链i-基序构象，其中两条平行双链以相反方向相互嵌入。每条双链通过平行链之间的半质子化C-C⁺碱基配对得以稳定，并且一串水分子将胞嘧啶的N4原子与磷酸根的O原子相连。d(ACCCT)的这种结构展示了分子间和分子内反向Hoogsteen碱基配对以及沃森-克里克碱基配对的实例，以稳定四链体。值得注意的是，四链复合物的一端通过一个三碱基氢键网络进一步稳定，其中两个腺嘌呤和一个胸腺嘧啶通过反向Hoogsteen碱基配对和不对称腺嘌呤-腺嘌呤碱基配对形成四个氢键。d(ACCCT)的结构与d(TAACCC)晶体结构中d(TAA)部分的局部结构相似，并提供了进一步的结构证据，表明这些碱基排列对于稳定这些新型DNA超二级结构至关重要。
