Biomembranes contain a wide variety of lipids and proteins within an essentially two-dimensional structure. The coexistence of such a large number of molecular species causes local tensions that frequently relax into a phase or compositional immiscibility along the lateral and transverse planes of the interface. As a consequence, a substantial microheterogeneity of the surface topography develops and that depends not only on the lipid-protein composition, but also on the lateral and transverse tensions generated as a consequence of molecular interactions. The presence of proteins, and immiscibility among lipids, constitute major perturbing factors for the membrane sculpturing both in terms of its surface topography and dynamics. In this work, we will summarize some recent evidences for the involvement of membrane-associated, both extrinsic and amphitropic, proteins as well as membrane-active phosphohydrolytic enzymes and sphingolipids in driving lateral segregation of phase domains thus determining long-range surface topography.
The lipids and proteins of biomembranes exhibit highly dissimilar conformations, geometrical shapes, amphipathicity, and thermodynamic properties which constrain their two-dimensional molecular packing, electrostatics, and interaction preferences. This causes inevitable development of large local tensions that frequently relax into phase or compositional immiscibility along lateral and transverse planes of the membrane. On the other hand, these effects constitute the very codes that mediate molecular and structural changes determining and controlling the possibilities for enzymatic activity, apposition and recombination in biomembranes. The presence of proteins constitutes a major perturbing factor for the membrane sculpturing both in terms of its surface topography and dynamics. We will focus on some results from our group within this context and summarize some recent evidence for the active involvement of extrinsic (myelin basic protein), integral (Folch-Lees proteolipid protein) and amphitropic (cFos and c-Jun) proteins, as well as a membrane-active amphitropic phosphohydrolytic enzyme (neutral sphingomyelinase), in the process of lateral segregation and dynamics of phase domains, sculpturing of the surface topography, and the bi-directional modulation of the membrane biochemical reactivity.
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