Jönsson Peter, Jönsson Bengt
Division of Physical Chemistry and ‡Division of Biophysical Chemistry, Lund University , SE-22100 Lund, Sweden.
Langmuir. 2015 Nov 24;31(46):12708-18. doi: 10.1021/acs.langmuir.5b03421. Epub 2015 Nov 13.
It has previously been observed that an externally applied hydrodynamic shear flow above a fluid lipid bilayer can change the local concentration of macromolecules that are associated with the lipid bilayer. The external liquid flow results in a hydrodynamic force on molecules protruding from the lipid bilayer, causing them to move in the direction of the flow. However, there has been no quantitative study about the magnitude of these forces. We here use finite element simulations to investigate how the magnitude of the external hydrodynamic forces varies with the size and shape of the studied macromolecule. The simulations show that the hydrodynamic force is proportional to the effective hydrodynamic area of the studied molecule, Ahydro, multiplied by the mean hydrodynamic shear stress acting on the membrane surface, σhydro. The parameter Ahydro depends on the size and shape of the studied macromolecule above the lipid bilayer and scales with the cross-sectional area of the molecule. We also investigate how hydrodynamic shielding from other surrounding macromolecules decreases Ahydro when the surface coverage of the shielding macromolecules increases. Experiments where the protein streptavidin is anchored to a supported lipid bilayer on the floor of a microfluidic channel were finally performed at three different surface concentrations, Φ = 1%, 6%, and 10%, where the protein is being moved relative to the lipid bilayer by a liquid flow through the channel. From photobleaching measurements of fluorescently labeled streptavidin we found the experimental drift data to be within good accuracy of the simulated results, less than 12% difference, indicating the validity of the results obtained from the simulations. In addition to giving a deeper insight into how a liquid flow can affect membrane-associated molecules in a lipid bilayer, we also see an interesting potential of using hydrodynamic flow experiments together with the obtained results to study the size and the intermolecular forces between macromolecules in membranes and lipid bilayers.
此前已经观察到，在流体脂质双分子层上方施加的外部流体动力剪切流可以改变与脂质双分子层相关的大分子的局部浓度。外部液体流会对从脂质双分子层突出的分子产生流体动力，使其沿流动方向移动。然而，尚未对这些力的大小进行定量研究。我们在此使用有限元模拟来研究外部流体动力的大小如何随所研究大分子的尺寸和形状而变化。模拟结果表明，流体动力与所研究分子的有效流体动力面积(A_{hydro})成正比，再乘以作用在膜表面的平均流体动力剪切应力(\sigma_{hydro})。参数(A_{hydro})取决于脂质双分子层上方所研究大分子的尺寸和形状，并与分子的横截面积成比例。我们还研究了当屏蔽大分子的表面覆盖率增加时，来自其他周围大分子的流体动力屏蔽如何降低(A_{hydro})。最后，在微流体通道底部的支撑脂质双分子层上固定蛋白质链霉亲和素的实验，在三种不同的表面浓度(\varPhi = 1%)、(6%)和(10%)下进行，其中蛋白质通过通道中的液体流相对于脂质双分子层移动。通过对荧光标记的链霉亲和素的光漂白测量，我们发现实验漂移数据与模拟结果的精度良好，差异小于(12%)，这表明模拟结果的有效性。除了更深入地了解液体流如何影响脂质双分子层中与膜相关的分子外，我们还看到了将流体动力流实验与所得结果结合起来研究膜和脂质双分子层中大分子的大小和分子间力的有趣潜力。
