Revisiting the Fluid Mosaic Model of Membranes

摘要

The fluid mosaic model, described over 20 years ago, characterized the cell membrane as "a two-dimensional oriented solution of integral proteins... in the viscous phos-pholipid bilayer" (1). This concept continues as the framework for thinking aboutthe dynamic structure of biomembranes, but certain aspects now need revision. Most membrane proteins do not enjoy the continuous, unrestricted lateral diffusion characteristic of a random, two-dimensional fluid. Instead, proteins diffuse in a more complicated way that indicates considerable lateral heterogeneity in membrane structure, at least on a nanometer scale. Certain proteins are transiently confined to small domains in seemingly undifferentiated membrane regions. Another surprise is that a few membrane proteins undergo rapid, forward-directed transport toward the cell edge, perhaps propelled by cytoskel-etal motors.