Li Zhidong, Wu Jianzhong, Wang Zhen-Gang
Department of Chemical and Environmental Engineering, University of California, Riverside, California 92521, USA.
Biophys J. 2008 Feb 1;94(3):737-46. doi: 10.1529/biophysj.107.112508. Epub 2007 Sep 21.
We present a theoretical model for aqueous solutions of double-stranded (ds) DNA with explicit consideration of electrostatic interactions, excluded-volume effects, van der Waals attractions, and salt ions. With reasonable parameters estimated from the DNA structure and experimental data for electrolytes, we are able to reproduce the DNA osmotic pressure in the bulk in good agreement with experiment. The predicted DNA osmotic pressure in lambda-bacteriophages is found to coincide with that of the PEG8000 solution that inhibits DNA ejection as reported in recent experiments. Based on the radial distributions of DNA segments and of counterions at different degrees of packaging, we find that in the presence of Mg(2+), DNA forms a multilayer structure near the inner surface of a fully loaded bacteriophage, but at low packing density the DNA segments are depleted from the surface owing to the local condensation of DNA induced by the divalent counterions. By contrast, the multilayer DNA structure is less distinctive in the presence of Na(+) despite the increase of the DNA density at contact, and the depletion near the capsid surface is not found at low packing density.
我们提出了一个双链（ds）DNA水溶液的理论模型，明确考虑了静电相互作用、排除体积效应、范德华引力和盐离子。通过从DNA结构和电解质实验数据估算出合理的参数，我们能够很好地再现本体中DNA的渗透压，与实验结果相符。发现预测的λ噬菌体中DNA的渗透压与近期实验报道的抑制DNA喷射的PEG8000溶液的渗透压一致。基于不同包装程度下DNA片段和抗衡离子的径向分布，我们发现，在Mg(2+)存在的情况下，DNA在完全装载的噬菌体内表面附近形成多层结构，但在低包装密度下，由于二价抗衡离子诱导的DNA局部凝聚，DNA片段从表面耗尽。相比之下，在Na(+)存在的情况下，尽管接触时DNA密度增加，但多层DNA结构不太明显，并且在低包装密度下未发现衣壳表面附近的耗尽现象。
