Institute for Physical Science and Technology, University of Maryland , College Park, Maryland 20742, United States.
J Phys Chem B. 2013 Oct 24;117(42):13107-14. doi: 10.1021/jp402922q. Epub 2013 Jul 12.
Using theoretical arguments and extensive Monte Carlo (MC) simulations of a coarse-grained three-dimensional off-lattice model of a β-hairpin, we demonstrate that the equilibrium critical force, Fc, needed to unfold the biopolymer increases nonlinearly with increasing volume fraction occupied by the spherical macromolecular crowding agent. Both scaling arguments and MC simulations show that the critical force increases as Fc ≈ φc(α). The exponent α is linked to the Flory exponent relating the size of the unfolded state of the biopolymer and the number of amino acids. The predicted power law dependence is confirmed in simulations of the dependence of the isothermal extensibility and the fraction of native contacts on φc. We also show using MC simulations that Fc is linearly dependent on the average osmotic pressure (P) exerted by the crowding agents on the β-hairpin. The highly significant linear correlation coefficient of 0.99657 between Fc and P makes it straightforward to predict the dependence of the critical force on the density of crowders. Our predictions are amenable to experimental verification using laser optical tweezers.
利用粗粒化的三维无格子β发夹模型的理论论证和广泛的蒙特卡罗（MC）模拟，我们证明了平衡临界力 Fc 随着球形大分子拥挤剂占据的体积分数的增加呈非线性增加。两种标度论证和 MC 模拟都表明，临界力增加为 Fc ≈ φc(α)。指数 α 与 Flory 指数相关，该指数与生物聚合物的展开状态的大小和氨基酸的数量有关。在模拟等温伸展性和天然接触分数对 φc 的依赖性时，预测的幂律依赖性得到了证实。我们还使用 MC 模拟表明，Fc 与拥挤剂对β发夹施加的平均渗透压（P）呈线性相关。Fc 和 P 之间的高度显著线性相关系数为 0.99657，这使得预测临界力对拥挤剂密度的依赖性变得非常简单。我们的预测可以使用激光光学镊子进行实验验证。
