Department of Mechanical Engineering, The Ohio State University, Columbus, OH, USA.
Electrophoresis. 2010 Aug;31(16):2813-21. doi: 10.1002/elps.201000081.
The electrophoresis of lambda-DNA is observed in a microscale converging channel where the center-of-masses trajectories of DNA molecules are tracked to measure instantaneous electrophoretic (EP) mobilities of DNA molecules of various stretch lengths and conformations. Contrary to the usual assumption that DNA mobility is a constant, independent of field and DNA length in free solution, we find DNA EP mobility varies along the axis in the contracting geometry. We correlate this mobility variation with the local stretch and conformational changes of the DNA, which are induced by the electric field gradient produced by the contraction. A "shish-kebab" model of a rigid polymer segment is developed, which consists of aligned spheres acting as charge and drag centers. The EP mobility of the shish-kebab is obtained by determining the electrohydrodynamic interactions of aligned spheres driven by the electric field. Multiple shish-kebabs are then connected end-to-end to form a freely jointed chain model for a flexible DNA chain. DNA EP mobility is finally obtained as an ensemble average over the shish-kebab orientations that are biased to match the overall stretch of the DNA chain. Using physically reasonable parameters, the model agrees well with experimental results for the dependence of EP mobility on stretch and conformation. We find that the magnitude of the EP mobility increases with DNA stretch, and that this increase is more pronounced for folded conformations.
在微尺度汇聚通道中观察到 lambda-DNA 的电泳，在该通道中，追踪 DNA 分子的质心轨迹以测量各种拉伸长度和构象的 DNA 分子的瞬时电泳（EP）迁移率。与通常的假设相反，即 DNA 迁移率是一个常数，与自由溶液中的场和 DNA 长度无关，我们发现 DNA 的 EP 迁移率在收缩几何形状中沿轴变化。我们将这种迁移率变化与 DNA 的局部拉伸和构象变化相关联，这些变化是由收缩产生的电场梯度引起的。开发了一种刚性聚合物段的“串珠串”模型，该模型由充当电荷和阻力中心的对齐球体组成。通过确定由电场驱动的对齐球体的电动流体动力学相互作用，可以获得串珠串的 EP 迁移率。然后将多个串珠串首尾相连，形成用于柔性 DNA 链的自由连接链模型。最后，通过对与 DNA 链的整体拉伸相匹配的串珠串取向进行系综平均，得到 DNA 的 EP 迁移率。使用合理的物理参数，该模型与实验结果在 EP 迁移率对拉伸和构象的依赖性方面吻合良好。我们发现，EP 迁移率的大小随 DNA 的拉伸而增加，并且对于折叠构象，这种增加更为明显。
