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双股寡聚d(G-C)6 DNA Z-构象的形成及其构象转换的动态研究
激光生物学报摘要 2005-5
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黄汝多1, 2， 李振华1, 2， Van de Sand J.H.2
（1.中国安徽大学生命科学学院，中国安徽 合肥230039；2.加拿大卡尔加里大学医药和医学生化系，健康研究中心 AlbataT2N 4N1，Calgary, Canada）
摘 要：研究揭示，生物信息的形成，传递与DNA构象的多样性，特别是其中的左手螺旋Z－构象DNA（Z-DNA）相关。在机体DNA链中，普遍存在的特异序列结构d(C-G)n和d(G-C)n片段易形成Z－构象。但对d(G-C)n序列结构的寡聚体Oligo-d(G-C)n，（n小于8）能转换形成Z-DNA片段少见报道。为促进对Z-DNA尤其是其中的短片段Z-DNA与生物功能的相关性研究，我们对合成并纯化后的寡聚体Oligo-d(G-C)n，n分别为4,6,8,10, 及Oligo-d(C-G)6和多聚体poly-d(G-C) 500-900进行Z-构象的形成和其构象转换的比较研究。研究结果发现：①d(GpCpGpCpGpCpGpCpGpCpGpC)是d(G-C)n序列结构中能转换形成Z-构象的最短片段（n＝6）。其转换成Z-构象能力有链长依赖性（poly d(G-C)500-900易于Oligo-d(G-C)6）；②Oligo-d(G-C)6的Z-构象形成能力因溶液中的介质性质不同而异。Co(NH3) 2+> Mg2+>Na+; C1O4->Cl-，因此要求盐溶液的浓度差异很大。③PH7.2，室温条件下，在MgCl2, NaClO4, NaCl溶液浓度分别由0 mol/L增至6.0 mol/L，Oligo-d(G-C)6的B、Z构象转换都出现：B-构象相对稳定期，B-、Z-构象转换跃迁期和Z-构象相对稳定期。每个阶段要求跨越的盐浓度变迁范围也因所用介质而异。当溶液中Oligo-d(G-C)6 B-构象、Z-构象各占50％（θ1/2）时，其盐浓度分分别为1.72mol/L(MgCl2),2.88 mol/L（NaClO4），3.85 mol/L（NaCl）。④Oligo-d(G-C)6的B-，Z-构象转换程度受盐浓度影响：当Oligo-d(G-C)6处于最适条件和不同盐溶液其浓度为θ1/2浓度时，温度由8℃→22℃，在MgCl2，NaClO4溶液中的Oligo-d(G-C)6形成Z-构象能力增加，当由22℃→60℃，MgCl2溶液中的Z-构象Oligo-d(G-C)6加速增加，而在NaClO4溶液中则是急速向B-型Oligo-d(G-C)6方向转换；温度变化对处于NaCl溶液中的Oligo-d(G-C)6B-、Z-构象相对平衡影响较小。⑤甲基化胞嘧啶即Oligo-d(G-mC)6或d(mC-G)6均增大Z-构象形成能力。⑥在4 mol/L MgCl2溶液中的Oligo-d(G-C)6或Oligo-d(C-G)6或poly d(G-C) 500-900的UVab谱、UVcd谱均显示出非B-型或Z-型DNA的新谱型。并且有链长依赖性和因溶液浓度改变出现构象可逆性转变。提示在Oligo-d(G-C)6的构象转换过程中可能存在新构象"X"型，即BZX构象转换模式。
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Studies on left-handed DNA:B to Z conformation transition of double strand oligo-d(G-C)6
HUANG Ru-duo 1,2, LI Zhen-hua 1,2, J.H. Van de Sande 2
(1. Department of Biology Anhui University, Hefei 230039, Anhui, China；2. Department of Medicine and Medical Biochemistry, University of Calgary, Alberta T2N 4N1， Calgary, Canada)
Abstract: Synthetic oligo-d(G-C)6 was induced to undergo B-Z conformation transition by appropriate high-salt solution as shown by ultraviolet and circular dichroism spectroscopy. Among the salts tested, MgCl2 had the most potent ability to induce the conformation transition of oligo-d(G-C)6, NaClO4 (5mol/L) could also induce the full transition and NaCl (5mol/L) induced only an incomplete transition (Ca. 70%). The effect of temperature on the B-Z conformation transition of oligo-d(G-C)6 varied with the kind of salts used. On the basis of the observation, duodecandeoxyribonucleotide-d(GpCpGpCpGpCpGpCpGpCpGpC) was the minimal sequence that would support left-handed conformation in aqueous salt solution. And the results show that, oligo-d(G-C)6, or oligo-d(C-G)6 in 4mol/L MgCl2 solution, the process of its conformation transition might be: BZX, "X", an unknown conformation form is present, it is may very helpful to make a complete search for the Biological function of Z-DNA..
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Bioinformatics,
sequence analysis; GCG; Life Science News; Drug Discovery.
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