Luo Zhonglong, Cheng Bo, Cui Shuxun
Key Lab of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, China.
Langmuir. 2015 Jun 9;31(22):6107-13. doi: 10.1021/acs.langmuir.5b01313. Epub 2015 May 28.
Water, the dominant component under the physiological condition, is a complicated solvent which greatly affects the properties of solute molecules. Here, we utilize atomic force microscope-based single-molecule force spectroscopy to study the influence of water on the single-molecule elasticity of an unstructured single-stranded RNA (poly(U)). In nonpolar solvents, RNA presents its inherent elasticity, which is consistent with the theoretical single-chain elasticity calculated by quantum mechanics calculations. In aqueous buffers, however, an additional energy of 1.88 kJ/mol·base is needed for the stretching of the ssRNA chain. This energy is consumed by the bound water rearrangement (Ew) during chain elongation. Further experimental results indicate that the Ew value is uncorrelated to the salt concentrations and stretching velocity. The results obtained in an 8 M guanidine·HCl solution provide more evidence that the bound water molecules around RNA give rise to the observed deviation between aqueous and nonaqueous environments. Compared to synthetic water-soluble polymers, the value of Ew of RNA is much lower. The weak interference of water is supposed to be the precondition for the RNA secondary structure to exist in aqueous solution.
水是生理条件下的主要成分，是一种复杂的溶剂，对溶质分子的性质有很大影响。在此，我们利用基于原子力显微镜的单分子力谱来研究水对无结构单链RNA（聚尿苷酸）单分子弹性的影响。在非极性溶剂中，RNA呈现其固有弹性，这与通过量子力学计算得出的理论单链弹性一致。然而，在水性缓冲液中，单链RNA链的拉伸需要额外的1.88 kJ/mol·碱基的能量。该能量在链伸长过程中被结合水重排（Ew）消耗。进一步的实验结果表明，Ew值与盐浓度和拉伸速度无关。在8 M盐酸胍溶液中获得的结果提供了更多证据，表明RNA周围的结合水分子导致了在水性和非水性环境之间观察到的偏差。与合成水溶性聚合物相比，RNA的Ew值要低得多。水的弱干扰被认为是RNA二级结构在水溶液中存在的前提条件。
