Wu Jun, Du Fen, Zhang Peng, Khan Izhar Ahmed, Chen Jie, Liang Yi
National Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China.
J Inorg Biochem. 2005 May;99(5):1145-54. doi: 10.1016/j.jinorgbio.2005.02.010.
Aluminum is a known neurotoxic agent and its neurotoxic effects may be due to its binding to DNA. However, the mechanism for the interaction of aluminum ions with DNA is not well understood. Here, we report the application of isothermal titration calorimetry (ITC), fluorescence spectroscopy, and UV spectroscopy to investigate the thermodynamics of the binding of aluminum ions to calf thymus DNA (CT DNA) under various pH and temperature conditions. The binding reaction is driven entirely by a large favorable entropy increase but with an unfavorable enthalpy increase in the pH range of 3.5-5.5 and at all temperatures examined. Aluminum ions show a strong and pH-dependent binding affinity to CT DNA, and a large positive molar heat capacity change for the binding, 1.57 kcal mol(-1) K(-1), demonstrates the burial of the polar surface of CT DNA upon groove binding. The fluorescence of ethidium bromide bound to CT DNA is quenched by aluminum ions in a dynamic way. Both Stern-Volmer quenching constant and the binding constant increase with the increase of the pH values, reaching a maximum at pH 4.5, and decline with further increasing the pH to 5.5. At pH 6.0 and 7.0, aluminum ions precipitate CT DNA completely and no binding of aluminum ions to CT DNA is observed by ITC. Combining the results from these three methods, we conclude that aluminum ions bind to CT DNA with high affinity through groove binding under aluminum toxicity pH conditions and precipitate CT DNA under physiological conditions.
铝是一种已知的神经毒性剂，其神经毒性作用可能归因于它与DNA的结合。然而，铝离子与DNA相互作用的机制尚未完全明确。在此，我们报道了运用等温滴定量热法（ITC）、荧光光谱法和紫外光谱法，来研究在不同pH值和温度条件下铝离子与小牛胸腺DNA（CT DNA）结合的热力学情况。在pH值为3.5 - 5.5的范围内以及所有检测的温度下，结合反应完全由大幅有利的熵增驱动，但伴有不利的焓增。铝离子对CT DNA表现出强烈且依赖于pH值的结合亲和力，结合过程中较大的正摩尔热容变化（1.57千卡·摩尔⁻¹·开⁻¹）表明，CT DNA的极性表面在沟槽结合时被掩埋。与CT DNA结合的溴化乙锭的荧光被铝离子以动态方式猝灭。斯特恩 - 沃尔默猝灭常数和结合常数均随pH值的升高而增加，在pH 4.5时达到最大值，进一步将pH值升高至5.5时则下降。在pH 6.0和7.0时，铝离子使CT DNA完全沉淀，ITC未观察到铝离子与CT DNA的结合。综合这三种方法的结果，我们得出结论：在铝毒性pH条件下，铝离子通过沟槽结合以高亲和力与CT DNA结合，而在生理条件下会使CT DNA沉淀。
