Lipid rafts, fluid/fluid phase separation, and their relevance to plasma membrane structure and function

Abstract

Novel biophysical approaches combined with modeling and new biochemical data have helped to recharge the lipid raft field and have contributed to the generation of a refined model of plasma membrane organization. In this review, we summarize new information in the context of previous literature to provide new insights into the spatial organization and dynamics of lipids and proteins in the plasma membrane of live cells. Recent findings of large-scale separation of liquid-ordered and liquid-disordered phases in plasma membrane vesicles demonstrate this capacity within the complex milieu of plasma membrane proteins and lipids. Roles for membrane heterogeneity and reorganization in immune cell activation are discussed in light of this new information.

Figure 1

Micron-scale fluid-fluid phase separation in giant unilamellar vesicles (GUVS) composed of cholesterol, SM, DOPC, and ganglioside GM₁. Tangential confocal section of GUV imaged at 23 ° C. Alexa488-cholera toxin B (A488-CTB) bound to Lo-preferring GM₁ partitions complementarily to the Ld-preferring carbocyanine lipid probe C12:0 DiI in phase separated GUVs (scale bar, 5 μm). Image adapted from ref. .

Figure 2

Giant plasma membrane vesicles (GPMVs) isolated from RBL-2H3 mast cells spontaneously phase separate into coexisting fluid phases. GPMVs were generated from cells pre-labeled with Alexa488-cholera toxin B and lissamine rhodamine B sulfonyl-DOPE (Rh-DOPE). Equatorial confocal section of a GPMV (~25 μm diameter) was imaged at 15° C. A488-CTB bound to GM₁ shows partitioning complementary to Rh-DOPE and prefers the Lo-phase in GPMVs. Image adapted from ref. .