Banyay Martina, Gräslund Astrid
Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, S-106 91 Stockholm, Sweden.
J Mol Biol. 2002 Dec 6;324(4):667-76. doi: 10.1016/s0022-2836(02)01104-x.
This FTIR investigation concerns structural consequences of 5-methylation of cytosine in a DNA decamer in solution. Methylation of DNA is an important functional signal in transcription, but its effect on DNA structure is variable and not fully understood. Here, single and multiple 5-methylcytosine substitutions are introduced into the self-complementary sequence d(CCGGCGCCGG)(2). No major structural effect of methylation on the DNA duplex in solution is seen in the IR spectra: The overall B-form character of the backbone and S-type of sugar puckering are maintained in all the studied sequences, in agreement with previous literature. However, certain significant effects are detected in the IR regions sensitive to sugar pucker and glycosidic torsional angle. A single or multiple 5-methylcytosine substitution in d(CCGGCGCCGG)(2) leads to a doublet splitting of the S-type 840-820 cm(-1) sugar conformational band. The results suggest the coexistence of two different major sugar puckers within the S-conformational family, with an increased relative contribution of the C2'-endo type of sugar in the methylated sequences. In addition, a partial or full downshift of the guanosine/anti marker band at 1,375 cm(-1) in the methylated sequences reflects a change in the value of the dihedral angle chi of guanosine upon methylation. The IR spectra are interpreted in terms of localized transitions between the BI and BII subconformational states of the B-DNA backbone caused by the methylation. An increased amount of the BII subconformer in the methylated sequences should give rise to a structurally more rigid conformation, in agreement with earlier observations on DNA backbone dynamics and bending flexibility in methylated DNA.
这项傅里叶变换红外光谱（FTIR）研究关注溶液中DNA十聚体中胞嘧啶5-甲基化的结构后果。DNA甲基化是转录过程中的一个重要功能信号，但其对DNA结构的影响具有多样性且尚未完全明确。在此，将单个和多个5-甲基胞嘧啶取代引入自互补序列d(CCGGCGCCGG)(2)。红外光谱显示，甲基化对溶液中的DNA双链体没有明显的结构影响：所有研究序列中，主链的整体B型特征和糖环的S型构象均得以维持，这与先前的文献一致。然而，在对糖环构象和糖苷扭转角敏感的红外区域检测到了某些显著影响。在d(CCGGCGCCGG)(2)中进行单个或多个5-甲基胞嘧啶取代会导致S型840 - 820 cm(-1)糖构象带出现双峰分裂。结果表明，在S型构象家族中存在两种不同的主要糖环构象，且甲基化序列中C2'-内型糖的相对贡献增加。此外，甲基化序列中1375 cm(-1)处鸟苷/反式标记带部分或完全下移，反映出甲基化后鸟苷二面角χ值的变化。红外光谱可根据甲基化导致的B-DNA主链BI和BII亚构象状态之间的局部转变来解释。甲基化序列中BII亚构象数量增加应会导致结构上更刚性的构象，这与先前关于甲基化DNA中DNA主链动力学和弯曲灵活性的观察结果一致。
