Wong J Y, Park C K, Seitz M, Israelachvili J
Department of Chemical Engineering, University of California, Santa Barbara, California 93106 USA.
Biophys J. 1999 Sep;77(3):1458-68. doi: 10.1016/S0006-3495(99)76993-6.
We have created phospholipid bilayers supported on soft polymer "cushions" which act as deformable substrates (see accompanying paper, Wong, J. Y., J. Majewski, M. Seitz, C. K. Park, J. N. Israelachvili, and G. S. Smith. 1999. Biophys. J. 77:1445-1457). In contrast to "solid-supported" membranes, such "soft-supported" membranes can exhibit more natural (higher) fluidity. Our bilayer system was constructed by adsorption of small unilamellar dimyristoylphosphatidylcholine (DMPC) vesicles onto polyethylenimine (PEI)-supported Langmuir-Blodgett lipid monolayers on mica. We used the surface forces apparatus (SFA) to investigate the long-range forces, adhesion, and fusion of two DMPC bilayers both above and below their main transition temperature (T(m) approximately 24 degrees C). Above T(m), hemi-fusion activation pressures of apposing bilayers were considerably smaller than for solid-supported bilayers, e.g., directly supported on mica. After separation, the bilayers naturally re-formed after short healing times. Also, for the first time, complete fusion of two fluid (liquid crystalline) phospholipid bilayers was observed in the SFA. Below T(m) (gel state), very high pressures were needed for hemi-fusion and the healing process became very slow. The presence of the polymer cushion significantly alters the interaction potential, e.g., long-range forces as well as fusion pressures, when compared to solid-supported systems. These fluid model membranes should allow the future study of integral membrane proteins under more physiological conditions.
我们制备了支撑在柔软聚合物“垫子”上的磷脂双层，这些“垫子”充当可变形的基底（见随附论文，Wong, J. Y., J. Majewski, M. Seitz, C. K. Park, J. N. Israelachvili, and G. S. Smith. 1999. Biophys. J. 77:1445 - 1457）。与“固体支撑”膜相比，这种“软支撑”膜能表现出更自然（更高）的流动性。我们的双层系统是通过将小单层二肉豆蔻酰磷脂酰胆碱（DMPC）囊泡吸附到云母上聚乙烯亚胺（PEI）支撑的朗缪尔 - 布洛杰特脂质单分子层上构建而成。我们使用表面力装置（SFA）研究了两个DMPC双层在其主转变温度（T(m)约为24℃）上下的长程力、粘附力和融合情况。在T(m)以上，相对的双层的半融合活化压力比固体支撑双层（例如直接支撑在云母上的双层）要小得多。分离后，双层在短时间愈合后自然重新形成。此外，首次在SFA中观察到两个流体（液晶）磷脂双层的完全融合。在T(m)以下（凝胶态），半融合需要非常高的压力，并且愈合过程变得非常缓慢。与固体支撑系统相比，聚合物垫子的存在显著改变了相互作用势，例如长程力以及融合压力。这些流体模型膜应该能让我们在更接近生理条件下对整合膜蛋白进行未来的研究。
