KINETIC AND EQUILIBRIUM-ANALYSIS OF A THREADING INTERCALATION MODE - DNA-SEQUENCE AND ION EFFECTS
KINETIC AND EQUILIBRIUM-ANALYSIS OF A THREADING INTERCALATION MODE - DNA-SEQUENCE AND ION EFFECTS
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DOI：
10.1021/bi00221a013
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发表时间：
1991-02-19
期刊：
影响因子：
2.9
通讯作者：
WILSON, WD
中科院分区：
文献类型：
--
作者：
TANIOUS, FA;YEN, SF;WILSON, WD
研究了对称萘二酰亚胺与烷基氨基取代基的相互作用，并与交替序列聚合物poly[d（A-T）]2和poly[d（G-C）]2进行了比较。 分光光度结合研究表明，虽然GC结合常数比AT结合常数大20-25倍，但二酰亚胺与两种序列的结合力很强。 盐浓度对结合平衡的影响的分析表明，二酰亚胺形成两个离子对在其复杂的两种聚合物作为一个简单的双阳离子预期。 停流动力学实验表明，二酰亚胺都协会和解离从DNA更慢，比经典的嵌入剂具有类似的结合常数。 盐浓度对解离动力学速率常数（k（d））的影响的分析表明，log k（d）对log [Na+]图中的斜率仅为在同一凹槽中具有两个带电基团的经典双阳离子嵌入剂所获得的值的大约一半。 这些动力学结果支持一个线程嵌入模型，一个带电的二酰亚胺取代基在每个DNA凹槽，而不是与两个侧链在同一个凹槽，与DNA的二酰亚胺复合物。 在用于解离穿线复合物的机制的速率决定步骤中，只有一个离子对被破坏;然后游离侧链可以在碱基对之间滑动以将两个二酰亚胺侧链置于同一凹槽中，并且这之后是二酰亚胺的快速完全解离。 离子对的这种顺序释放使得双阳离子穿层嵌入剂的解离斜率与经典单阳离子嵌入配体的斜率更相似。 动力学研究，因此，提供了一个非常明确的方法来区分经典的线程嵌入剂。 类似的实验也可以区分嵌入和沟槽结合模式。
The interaction of a symmetric naphthalene diimide with alkylamino substituents at each imide position was investigated with the alternating sequence polymers, poly[d(A-T)]2 and poly[d(G-C)]2. Spectrophotometric binding studies indicate strong binding of the diimide to both sequences although the GC binding constant is 20-25 times larger than the AT binding constant. Analysis of the effects of salt concentration on the binding equilibria shows that the diimide forms two ion pairs in its complex with both polymers as expected for a simple dication. Stopped-flow kinetics experiments demonstrate that the diimide both associates and dissociates from DNA more slowly than classical intercalators with similar binding constants. Analysis of salt concentration effects on dissociation kinetics rate constants (k(d)) reveals that slopes in log k(d) versus log [Na+] plots are only approximately half the value obtained for classical dicationic intercalators that have both charged groups in the same groove. These kinetics results support a threading intercalation model, with one charged diimide substituent in each of the DNA grooves rather than with both side chains in the same groove, for the diimide complex with DNA. In the rate-determining step of the mechanism for dissociation of a threading complex only one ion pair is broken; the free side chain can then slide between base pairs to put both diimide side chains in the same groove, and this is followed by rapid full dissociation of the diimide. This sequential release of ion pairs makes the dissociation slope for dicationic threading intercalators more similar to the slope for classical monocationic intercalating ligands. Kinetics studies, thus, provide a very clear method for distinguishing classical from threading intercalators. Similar experiments can also distinguish intercalation from groove binding modes.