Luo Zhaoxu, Wang Yanwei, Li Shuhang, Yang Guangcan
College of Mathematical, Physics and Electronic Information Engineering, Wenzhou University, Wenzhou 325035, China.
Polymers (Basel). 2018 Apr 2;10(4):394. doi: 10.3390/polym10040394.
It is well known that common trivalent counter ions can induce DNA compaction or condensation but are unable to invert DNA surface charge in a normal aqueous solution. In the present study, we found that trivalent-hydrolysed metal ions (Fe, Al) are not only capable of inducing DNA condensation, but they also invert the electrophoretic mobility of DNA by electrophoretic light scattering and single molecular techniques. In comparison with neutral trivalent cations, hydrolysed metal ions such as Fe can induce DNA condensation at a much lower concentration of cations, and its corresponding morphology of condensed DNA was directly observed by atomic force microscopy (AFM). The condensing and unravelling forces of DNA condensates were measured by tethering DNA by magnetic tweezers (MT) measurements at various concentration of Fe and Al. We found that a coil⁻globule transition of DNA by hydrolysed metal ions not only was observed in DNA-complex sizes, but also in the curve of electrophoretic mobility of DNA in solution. In contrast, the transition was not observed in the case of neutral trivalent cations such as La and Co. We attribute the transition and charge inversion to the ion-specific interaction between hydrolysed metal ions and phosphates of DNA backbone.
众所周知，常见的三价抗衡离子可诱导DNA压缩或凝聚，但在正常水溶液中无法反转DNA表面电荷。在本研究中，我们发现三价水解金属离子（铁、铝）不仅能够诱导DNA凝聚，还能通过电泳光散射和单分子技术反转DNA的电泳迁移率。与中性三价阳离子相比，水解金属离子如铁能够在阳离子浓度低得多的情况下诱导DNA凝聚，并且通过原子力显微镜（AFM）直接观察到了凝聚DNA的相应形态。通过在不同浓度的铁和铝下用磁镊（MT）测量拴系DNA来测定DNA凝聚物的凝聚和解开力。我们发现，水解金属离子导致的DNA从线圈到球体的转变不仅在DNA - 复合物大小中观察到，而且在溶液中DNA电泳迁移率曲线中也观察到。相比之下，在中性三价阳离子如镧和钴的情况下未观察到这种转变。我们将这种转变和电荷反转归因于水解金属离子与DNA主链磷酸根之间的离子特异性相互作用。
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