BINDING OF 4',6-DIAMIDINO-2-PHENYLINDOLE (DAPI) TO AT REGIONS OF DNA - EVIDENCE FOR AN ALLOSTERIC CONFORMATIONAL CHANGE
BINDING OF 4',6-DIAMIDINO-2-PHENYLINDOLE (DAPI) TO AT REGIONS OF DNA - EVIDENCE FOR AN ALLOSTERIC CONFORMATIONAL CHANGE
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DOI：
10.1021/bi00063a009
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发表时间：
1993-03-30
期刊：
影响因子：
2.9
通讯作者：
NORDEN, B
中科院分区：
文献类型：
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作者：
ERIKSSON, S;KIM, SK;NORDEN, B
用流动线性二色性（LD）、诱导圆二色性（CD）和荧光光谱研究了4 '，6-二脒基-2-苯基吲哚（DAPI）与几种双螺旋聚寡核苷酸和寡核苷酸在溶液中的相互作用。在富含AT的序列中，DAPI优先结合，LD表明分子以与螺旋轴约45度的角度侧边插入小沟中。这种结合几何形状被发现为非常低以及相当高的结合比。所得出的几何形状与具有Drew-Dickerson十二聚体的晶体中的DAPI复合物的几何形状一致，并且验证了溶液中具有该十二聚体的DAPI复合物在低结合率下具有与具有[poly（dA-dT）]2的复合物相似的ICD光谱。观察到DAPI与DNA结合以及与[poly（dA-dT）]2相互作用的两种CD光谱特征，表明第一种结合模式，尽管其表观丰度较低（百分之几），但不是由于特定的DNA位点。该效应可以用变构结合来解释，使得当DAPI分子与AT序列连续结合时，后者的构象改变。根据LD，新的构象似乎比正常的B型DNA更硬，这是DAPI发色团中第二种诱导CD光谱的原因。虽然光谱结果表明DNA构象的变化，与变构结合模型一致，但它们并不明确需要任何协同性，但偶然的邻居也可以解释这些数据。
The interaction of 4',6-diamidino-2-phenylindole (DAPI) with several double-helical poly- and oligonucleotides has been studied in solution using optical spectroscopic techniques: flow linear dichroism (LD), induced circular dichroism (CD), and fluorescence spectroscopy. In AT-rich sequences, where DAPI is preferentially bound, LD indicates that the molecule is edgewise inserted into the minor groove at an angle of approximately 45-degrees to the helix axis. This binding geometry is found for very low as well as quite high binding ratios. The concluded geometry is in agreement with that of the DAPI complex in a crystal with the Drew-Dickerson dodecamer, and the DAPI complex with this dodecamer in solution is verified to have an ICD spectrum similar to that of the complex with [poly(dA-dT)]2 at low binding ratios. The observation of two types of CD spectra characteristic for the binding of DAPI to DNA, and also for the interaction with [poly(dA-dT)]2, demonstrates that the first binding mode, despite its low apparent abundance (a few percent), is not due to a specific DNA site. The effect may be explained in terms of an allosteric binding such that when DAPI molecules bind contiguously to the AT sequence the conformation of the latter is changed. The new conformation, which according to LD appears to be stiffer than normal B-form DNA, is responsible for the second type of induced CD spectrum in the DAPI chromophore. Although the spectroscopic results indicate a change of DNA conformation, consistent with an allosteric binding model, they do not explicitly require any cooperativity, but accidental neighbors could also explain the data.