Komaba Institute for Science, The University of Tokyo, Komaba 3-8-1, Meguro, Tokyo 153-8902, Japan.
Department of Applied Physics, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Koganei, Tokyo 184-8588, Japan.
Langmuir. 2021 Jan 12;37(1):437-444. doi: 10.1021/acs.langmuir.0c03086. Epub 2020 Dec 22.
Membranes are ubiquitous structures in cells. The effects of membranes on various functional molecules have been reported, but their behaviors under macromolecular crowding and cell-sized confinement have not fully been understood. In this study, we model an intracellular environment by crowding micrometer-sized droplets and investigate the effects of membrane properties on molecular diffusion. The molecular diffusion inside small droplets covered with a lipid layer of phosphatidylcholine (PC) becomes slower compared with that of the corresponding bulk solutions under a crowding condition of polysaccharide dextran but not of its monomer unit, glucose. The addition of a poly(ethylene glycol) conjugated lipid (PEGylated lipid) to the PC membrane significantly alters the degree of slow diffusion observed inside small droplets of concentrated dextran. Interestingly, the change is not monotonic against dextran concentration; that is, the PEGylated membrane increases and decreases the degree of slow diffusion with increasing dextran concentration. We explain the nonmonotonic alternation from the increase in effective dextran concentration and the hindered temporal adsorption of dextran to the membrane. Because diffusion alteration by adding PEGylated lipid is observed for condensed small droplets of linear polymer PEG and hydrophilic protein bovine serum albumin, the phenomenon is general for other polymer systems as well. Furthermore, our findings may facilitate the understanding of intracellular molecular behaviors based on membrane effects as well as the development of numerous applications using polymer droplets.
细胞膜是细胞中普遍存在的结构。已经有报道称，细胞膜对各种功能分子有影响，但在大分子拥挤和细胞大小限制下的行为尚未完全理解。在这项研究中，我们通过拥挤微米大小的液滴来模拟细胞内环境，并研究膜性质对分子扩散的影响。在拥挤的多糖葡聚糖条件下，与相应的体相溶液相比，覆盖有磷脂酰胆碱（PC）脂质层的小液滴内的分子扩散变得更慢，但在其单体单元葡萄糖的情况下则不然。将聚乙二醇化脂质（PEGylated 脂质）添加到 PC 膜中会显著改变在高浓度葡聚糖小液滴内观察到的缓慢扩散程度。有趣的是，这种变化不是单调的，而是随着葡聚糖浓度的增加而增加和减少缓慢扩散的程度。我们从有效葡聚糖浓度的增加和葡聚糖对膜的时空吸附受阻来解释这种非单调的交替。由于添加 PEGylated 脂质会导致线性聚合物 PEG 和亲水性蛋白质牛血清白蛋白的凝聚小液滴的扩散发生改变，因此这种现象对于其他聚合物系统也是普遍存在的。此外，我们的发现可能有助于基于膜效应理解细胞内分子行为，以及利用聚合物液滴开发众多应用。
