ACS Nano. 2019 Aug 27;13(8):8946-8956. doi: 10.1021/acsnano.9b02811. Epub 2019 Jul 16.
The cellular cytoplasm is crowded with macromolecules and other species that occupy up to 40% of the available volume. Previous studies have reported that for high crowder molecule concentrations, colloidal tracer particles have a dampened diffusion due to the higher solution viscosity. However, these studies employed uniform distributions of crowder molecules. We report a scenario, previously unexplored experimentally, of increased tracer transport driven by a nonuniform concentration of crowder macromolecules. In gradients of a polymeric crowder, tracer particles undergo transport several times higher than that of their bulk diffusion rate. The direction of the transport is toward regions of lower crowder concentration. Mechanistically, hard-sphere interactions and the resulting volume exclusion between the tracer and crowder increase the effective diffusion by inducing a convective motion of tracers, which we explain through modeling. Strikingly, soft deformable particles show even greater enhancement in transport in crowder gradients compared to similarly sized hard particles. Overall, this demonstration of enhanced transport in nonuniform distributions of crowders is anticipated to clarify aspects of multicomponent intracellular transport.
细胞质中充满了大分子和其他物质，它们占据了可用体积的 40%。以前的研究报告指出，对于高浓度的拥挤分子，胶体示踪粒子由于溶液粘度增加而扩散减弱。然而，这些研究采用了均匀分布的拥挤分子。我们报告了一种以前未在实验中探索过的情况，即由于拥挤大分子的非均匀浓度，示踪剂的运输增加。在聚合物拥挤物的梯度中，示踪粒子的运输速度比其体相扩散速度高几倍。运输的方向是朝着拥挤物浓度较低的区域。从力学上讲，示踪剂和拥挤物之间的硬球相互作用和由此产生的体积排斥增加了有效扩散，我们通过建模对此进行了解释。引人注目的是，与同样大小的硬粒子相比，软变形粒子在拥挤物梯度中的传输增强更为显著。总的来说，这种在非均匀拥挤物分布中增强传输的演示有望澄清多组分细胞内运输的各个方面。
