LIPID DOMAINS AND LIPID-PROTEIN INTERACTIONS IN BIOLOGICAL-MEMBRANES

In the fluid mosaic model of membranes, lipids are organized in the fo rm of a bilayer supporting peripheral and integral proteins. This mode l considers the lipid bilayer as a two-dimensional fluid in which lipi ds and proteins are free to diffuse. As a direct consequence, both typ es of molecules would be expected to be randomly distributed within th e membrane. In fact, evidences are accumulating to indicate the occurr ence of both a transverse and lateral regionalization of membranes whi ch can be described in terms of micro- and macrodomains, including the two leaflets of the lipid bilayer. The nature of the interactions res ponsible for the formation of domains, the way they develop and the ti me- and space-scale over which they exist represent today as many chal lenging problems in membranology. In this report, we will first consid er some of the basic observations which point to the role of proteins in the transverse and lateral regionalization of membranes. Then, we w ill discuss some of the possible mechanisms which, in particular in te rms of lipid/protein interactions, can explain lateral heterogenities in membranes and which have the merit of providing a thermodynamic sup port to the existence of lipid domains in membranes.