Taquet A, Labarbe R, Houssier C
Laboratoire de Chimie Macromoléculaire et Chimie Physique, Université de Liège, Belgium.
Biochemistry. 1998 Jun 23;37(25):9119-26. doi: 10.1021/bi972735v.
We have investigated the thermodynamic aspects of the ligand binding to chromatin, using isothermal titration calorimetry. Two classical DNA ligands were used: an intercalator, ethidium bromide, and a minor groove binder, netropsin. Stoichiometry, affinity constant, and thermodynamic parameters were determined at various salt concentrations and different temperatures. The effect of ionic strength was analyzed according to the Record theory applied to chromatin. We also compared the binding parameters on naked DNA, H1/H5-depleted chromatin, and chromatin. We demonstrated that the presence of histones on DNA still allows the ligand binding that takes place according to a simple one single-site model. For both ligand types, the thermodynamic driving force is enthalpic and the association is characterized by a somewhat weaker affinity and more scattered ligand distribution than on naked DNA. The ligand affinity is weakly altered by the salt-induced compaction of the chromatin and the binding is accompanied by a release of one counterion per ligand molecule. The temperature-dependent studies revealed the existence of a small heat capacity change associated with ligand binding to chromatin, together with an enthalpy-entropy compensation that maintains the free energy constant over the investigated temperature range.
我们使用等温滴定量热法研究了配体与染色质结合的热力学方面。使用了两种经典的DNA配体：一种嵌入剂溴化乙锭和一种小沟结合剂纺锤菌素。在不同的盐浓度和不同温度下测定了化学计量、亲和常数和热力学参数。根据应用于染色质的Record理论分析了离子强度的影响。我们还比较了裸DNA、H1/H5缺失染色质和染色质上的结合参数。我们证明DNA上组蛋白的存在仍然允许配体结合，这种结合根据简单的单一位点模型发生。对于两种配体类型，热力学驱动力是焓驱动的，并且与裸DNA相比，缔合的特征是亲和力稍弱且配体分布更分散。配体亲和力受盐诱导的染色质压缩影响较弱，并且结合伴随着每个配体分子释放一个抗衡离子。温度依赖性研究揭示了与配体结合到染色质相关的小的热容变化，以及在研究的温度范围内维持自由能常数的焓-熵补偿。
