Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 7610001, Israel;
Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106;
Proc Natl Acad Sci U S A. 2021 Nov 30;118(48). doi: 10.1073/pnas.2113202118.
Lipid membranes are complex quasi-two-dimensional fluids, whose importance in biology and unique physical/materials properties have made them a major target for biophysical research. Recent single-molecule tracking experiments in membranes have caused some controversy, calling the venerable Saffman-Delbrück model into question and suggesting that, perhaps, current understanding of membrane hydrodynamics is imperfect. However, single-molecule tracking is not well suited to resolving the details of hydrodynamic flows; observations involving correlations between multiple molecules are superior for this purpose. Here dual-color molecular tracking with submillisecond time resolution and submicron spatial resolution is employed to reveal correlations in the Brownian motion of pairs of fluorescently labeled lipids in membranes. These correlations extend hundreds of nanometers in freely floating bilayers (black lipid membranes) but are severely suppressed in supported lipid bilayers. The measurements are consistent with hydrodynamic predictions based on an extended Saffman-Delbrück theory that explicitly accounts for the two-leaflet bilayer structure of lipid membranes.
脂质膜是复杂的准二维流体，其在生物学中的重要性和独特的物理/材料特性使其成为生物物理研究的主要目标。最近在膜中的单分子跟踪实验引起了一些争议，质疑了古老的 Saffman-Delbrück 模型，并表明当前对膜流动力学的理解可能并不完美。然而，单分子跟踪不适合解析流体力学流动的细节；涉及多个分子之间相关性的观察对于这个目的更为优越。在这里，使用具有亚毫秒时间分辨率和亚微米空间分辨率的双色分子跟踪来揭示膜中荧光标记脂质对布朗运动的相关性。这些相关性在自由浮动的双层（黑质脂质膜）中延伸数百纳米，但在支撑脂质双层中受到严重抑制。这些测量结果与基于扩展的 Saffman-Delbrück 理论的流体动力学预测一致，该理论明确考虑了脂质膜的双层结构。
