Figure 1.

Models of cell membrane organization discussed in Section 1.1. (A) “Fluid mosaic” model. Proteins are distributed randomly through a homogenous phospholipid bilayer. (B) “Lipid raft” model. Sphingolipid and cholesterol patches are populated with proteins which have an affinity for these patches. Protein species can be raft associated or nonraft associated. (C) “Lipid shell” model. Some proteins will be targeted to self-assembled cholesterol and sphingolipid complexes which form a “lipid shell” around the protein. These “lipid shells” have an affinity for, and can coalesce with, larger lipid domains. (D) “Picket Fence” model. Transmembrane proteins are restricted in their diffusion by actin filaments (the “fence”) which appose and run parallel to the cytoplasmic leaflet of the membrane, and by other transmembrane proteins bound to these filaments (“pickets”, not shown). (E) “Active composite” model. Short actin filaments adjacent to the cytoplasmic membrane leaflet are arranged in “asters”. Transmembrane proteins and GPI-anchored proteins are advected by actin and myosin to the centers of these asters, resulting in protein nanoclustering. See Section 1.1 for more detail. Readers please note that depictions of cell membranes here do not show as much protein (relative to lipid) as would be found in actual cell membranes. (See color plate)