DNA分子电荷逆转动力学和溶剂调控的单分子研究

The aggregation and conformational changes of charged biological macromolecules, such as DNA and protein, can not be explained by Poisson-Boltzmann theory. This process, such as DNA condensation, is closely linked to the basic phenomena of life and has an application of gene therapy. Generally, it is assumed that the process is related with ion - ion correlation, charge reversal, as well as solvent environment, but the specific mechanism is not yet fully clear. Recently, we developed a single-molecule electrophoresis technique and found that the charge reversal of the process is several orders of magnitude slower than the result of theoretical simulation of DNA molecules in multi-valent ion solution. This project plan to systematically study the kinetic mechanism of the charge reversal of DNA molecules in multi-valent ion solution.Electrophoresis of the biological single-molecule, magnetic tweezers and dynamic light scattering are the main tools in the study for DNA of different lengths, different multivalent ions through the solvent(such as alcohol, acids) to adjust the relative dielectric constant of the solution. The measurement of the characteristic time and the critical condition of charge reversal of DNA is achieved by single molecule electrophoresis. In the mean while, single molecule force spectroscopy and single molecular morphology by AFM are applied to the charge reversal and solvent effect study. Based on experimental data and the basic principles of physics, we try to constructhe phenomenological explanation of DNA charge reversal dynamics and further to find out the microscopic physical mechanism of the phenomenon.It will enrich and improve the electrostatic theory in solution.

带电生物大分子，其聚集和构型变化，无法用传统的Poisson-Boltzmann理论解释，而这一过程与生命基本现象和基因治疗应用密切相关。一般认为，涉及离子-离子关联，电荷逆转现象以及介质环境，但具体机制需要进一步研究。最近，我们利用自己开发的单分子电泳技术发现，DNA分子电荷逆转的过程要比理论模拟慢几个数量级。本课题计划用单分子技术深入研究这个发现并探索DNA分子电荷逆转的动力学机制。以单分子电泳，磁镊和动态光散射为主要手段来研究DNA分子的电荷逆转过程和溶剂对构型变化的影响。针对不同长度的DNA分子，不同的多价平衡离子，同时通过调节溶液的相对介电常数，测量电荷逆转的特征时间，找出电泳迁移率逆转临界点，解析DNA凝聚和解凝聚过程中的单分子力谱和形态，发现构型变化的新规律。根据实验数据和基本原理，提出电荷逆转动力学的唯象解释，同时搞清微观物理机制，丰富和完善溶液中的电荷作用理论。

带电生物大分子，其聚集和构型变化，与生命基本现象和基因治疗应用密切相关。本课题计划用单分子技术深入研究这个发现并探索DNA分子电荷逆转的动力学机制，取得了以下成果：.1.首先观察到了3价平衡离子条件下的DNA电荷逆转。系统研究了介电环境对DNA分子电荷逆转的影响，发现：在3价平衡离子中，如果将介电常数降低，可以实现DNA分子的电荷逆转。.2.深入研究了平衡离子的混合对DNA电荷逆转的影响。发现在4价离子溶液中加入1价和2 价离子,对DNA的电荷逆转起到抑制作用,而3价离子对DNA 的电荷逆转起促进作用，建立了这一机制的物理模型。.3.研究了pH值对DNA电荷逆转的影响，发现pH值降低对DNA电荷逆转有促进作用。.本项目所取得的研究成果共发表SCI论文8篇，其他论文1篇。超过项目立项时所预计的目标。还有一批成果在整理发表中。.部分由于项目所取得的成果，项目负责人被英国自然出版集团旗下期刊《Scientific Reports》聘为编委（Editorial Board Member）。Springer出版集团邀请负责人为Bacterial Chromatin: Methods in Molecular Biology 编写Dynamic light scattering of DNA-ligand complexes一章。