LONG-RANGE ALLOSTERIC EFFECTS ON THE B TO Z EQUILIBRIUM BY DAUNOMYCIN
LONG-RANGE ALLOSTERIC EFFECTS ON THE B TO Z EQUILIBRIUM BY DAUNOMYCIN
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DOI：
10.1021/bi00346a067
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发表时间：
1985-01-01
期刊：
影响因子：
2.9
通讯作者：
CHAIRES, JB
中科院分区：
文献类型：
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作者：
CHAIRES, JB
采用光谱法和荧光法研究了抗癌药物道诺霉素在不同溶液条件下与聚[d(G-C)]和聚[d(G-m5C)]的结合。在有利于左手Z构象的高盐条件下，药物与poly[d(G-C)]相互作用的结合等温线是s型的，表明了一个协同结合过程。协同结合的开始和程度都强烈依赖于离子强度。结合数据可以用一个模型来解释，在这个模型中，药物优先结合到B型DNA上，并作为B- Z平衡的变构效应物。在2.4 M NaCl下，每20个碱基对（bp）结合一个药物分子就会导致poly[d(G-C)]从Z形式完全转化为B形式，这是由结合数据推断出来的，并通过圆二色性测量直接证明。聚[d-(G-m5C)]在50 mM NaCl和1.25 mM MgCl2中得到了类似的结果。在这些溶液条件下，可以通过沉降速度和对dna酶I消化的敏感性等附加方法来证明poly[d(G-m5C)]中Z到B的结构转变是结合药物的函数。变构作用在20bp以上的传递远远超出了药物结合位点3bp的范围。由于道诺霉素优先结合嘌呤-嘧啶交替序列，这是唯一能够从B到Z转变的序列，因此本文描述的变构效应可能对理解药物抑制DNA复制事件的机制很重要。所描述的结果作为对DNA构象的远程变构效应的说明具有更普遍的兴趣，可能在基因表达的调节中具有普遍的重要性。
Spectroscopic and fluorometric methods were used to study the binding of the anticancer drug daunomycin to poly[d(G-C)] and poly[d(G-m5C)] under a variety of solution conditions. Under high-salt conditions that favor the left-handed Z conformation, binding isotherms for the interaction of the drug with poly[d(G-C)] are sigmoidal, indicative of a cooperative binding process. Both the onset and extent of the cooperative binding are strongly dependent upon the ionic strength. The binding data may be explained by a model in which the drug preferentially binds to B-form DNA and acts as an allosteric effector on the B to Z equilibrium. At 2.4 M NaCl, binding of as little as one drug molecule per 20 base pairs (bp) results in the conversion of poly[d(G-C)] from the Z form entirely to the B form, as inferred from binding data and demonstrated directly by circular dichroism measurements. Similar results are obtained for poly[d-(G-m5C)] in 50 mM NaCl and 1.25 mM MgCl2. Under these solution conditions, it is possible to demonstrate the Z to B structural transition in poly[d(G-m5C)] as a function of bound drug by the additional methods of sedimentation velocity and susceptibility to DNase I digestion. The transmission of allosteric effects over 20 bp is well beyond the range of the drug''s binding site of 3 bp. Since daunomycin preferentially binds to alternating purine-pyrimidine sequences, which are the only sequences capable of the B to Z transition, the allosteric effects described here may be of importance toward understanding the mechanism by which the drug inhibits DNA replicative events. The results described are of more general interest as an illustration of long-range allosteric effects on DNA conformation, of perhaps general importance in the regulation of gene expression.