Moon J H, Kim S K, Sehlstedt U, Rodger A, Nordén B
Department of Chemistry, Yeungnam University, Kyoungbuk, Republic of Korea.
Biopolymers. 1996 May;38(5):593-606. doi: 10.1002/(SICI)1097-0282(199605)38:5%3C593::AID-BIP5%3E3.0.CO;2-N.
The complexes of Hoechst 33258 with poly[d(A-T)2], poly[d(I-C)2], and poly[d(G-C)2], and poly[d(G-m5C)2] were studied using linear dichroism, CD, and fluorescence spectroscopies. The Hoechst-poly[d(I-C)2] complex, in which there is no guanine amino group protruding in the minor groove, exhibits spectroscopic properties that are very similar to those of the Hoechst-poly[d(A-T)2] complex. When bound to both of these polynucleotides, Hoechst exhibits an average orientation angle of near 45 degrees relative to the DNA helix axis for the long-axis polarized low-energy transition, a relatively strong positive induced CD, and a strong increase in fluorescence intensity--leading us to conclude that this molecule also binds in the minor groove of poly[d(I-C)2]. By contrast, when bound to poly[d(G-C)2] and poly[d(G-m5C)2], Hoechst shows a distinctively different behavior. The strongly negative reduced linear dichroism in the ligand absorption region is consistent with a model in which part of the Hoechst chromophore is intercalculated between DNA bases. From the low drug:base ratio onset of excitonic effects in the CD and fluorescence emission spectra, it is inferred that another part of the Hoechst molecule may sit in the major groove of poly[d(G-C)2] and poly[d(G-m5C)2] and preferentially stacks into dimers, though this tendency is strongly reduced for the latter polynucleotide. Based on these results, the importance of the interactions of Hoechst with the exocyclic amino group of guanine and the methyl group of cytosine in determining the binding modes are discussed.
利用线性二色性、圆二色性和荧光光谱学研究了Hoechst 33258与聚[d(A-T)2]、聚[d(I-C)2]、聚[d(G-C)2]和聚[d(G-m5C)2]的复合物。在Hoechst-聚[d(I-C)2]复合物中，小沟中没有突出的鸟嘌呤氨基，其光谱性质与Hoechst-聚[d(A-T)2]复合物非常相似。当与这两种多核苷酸结合时，对于长轴极化的低能跃迁，Hoechst相对于DNA螺旋轴的平均取向角接近45度，诱导圆二色性相对较强且为正，荧光强度大幅增加，这使我们得出结论，该分子也结合在聚[d(I-C)2]的小沟中。相比之下，当与聚[d(G-C)2]和聚[d(G-m5C)2]结合时，Hoechst表现出明显不同的行为。配体吸收区域强烈的负向还原线性二色性与一种模型一致，即Hoechst发色团的一部分插入DNA碱基之间。从CD和荧光发射光谱中激子效应在低药物：碱基比时开始出现，可以推断Hoechst分子的另一部分可能位于聚[d(G-C)2]和聚[d(G-m5C)2]的大沟中，并优先堆叠成二聚体，尽管后一种多核苷酸的这种趋势大大降低。基于这些结果，讨论了Hoechst与鸟嘌呤的环外氨基和胞嘧啶的甲基之间的相互作用在确定结合模式中的重要性。
