Membrane Nanodomains

Abstract

Biomembranes are assumed to contain lateral heterogeneities, usually called domains. When they are less than ∼100 nm in diameter, they are referred to as nanodomains. Biological nanodomains have been properly identified only in the twenty first century, largely through the advent of super‐resolution microscopy techniques. Size, irrespective of lifetime, is used as a defining parameter for nanodomains. The main methods used in these studies span from the arguably earliest atomic force microscopy detection of nanodomains in a lipid bilayer, in year 2000, to the most recent observations in living cells of synapsis, receptors, exocytosis or plant membranes, based on advanced fluorescence microscopy techniques. Key Concepts Nanodomains are lateral inhomogeneities in lipid bilayers or in cell membranes, of varying lifetimes, and diameters usually below ≈200 nm. Nanodomains are stabilised by low line tensions and high dipole–dipole interactions and crowding pressures. Observation of nanodomains requires the use of atomic force microscopy and super‐resolution fluorescence microscopy as the main tools.

Multi-dimensional and spatiotemporal correlative imaging at the plasma membrane of live cells to determine the continuum nano-to-micro scale lipid adaptation and collective motion

“…For instance, when D rat = 1, membrane diffusion is Brownian; however, when D rat <1 membrane diffusion is trapped, since its lipid molecular constituents’ diffusion is hindered because the dye is sensing the presence of highly condensed nanodomains. Trapped diffusion in condensed membranes resembles the previously described lipid diffusion in liquid ordered phases surrounded by lipids moving in a more fluid or liquid disordered phases; overall, forming liquid–liquid immiscible membranes 30,38,78,79 .…”

“…These studies have shown that collective interactions between sterols and saturated lipids induce the formation of condensed ‘liquid ordered’ (Lo) phases coexisting with ‘liquid disordered’ (Ld) phases, where the Lo phase displayed slower lateral diffusion. Heterogeneously distributed lipid nanodomains at the plasma membrane of cells, often referred to as rafts, are characterized by a dense lipid lateral packing, nanoscopic enrichment in sterols and saturated acyl chains, a transient lifetime, and a slow internal molecular diffusion 28–30 . Several methods have been developed to measure lipid diffusion 11,31–36 to indirectly report on lipid nanodomain formation and protein diffusional hindering 37,38 .…”

Multi-dimensional and spatiotemporal correlative imaging at the plasma membrane of live cells to determine the continuum nano-to-micro scale lipid adaptation and collective motion

“…For instance, when D rat = 1, membrane diffusion is Brownian; however, when D rat < 1 membrane diffusion is trapped, since its lipid molecular constituents' diffusion is hindered because the dye is sensing the presence of highly condensed nanodomains. Trapped diffusion in condensed membranes resembles the previously described lipid diffusion in Lo phases surrounded by lipids moving in a more fluid or Ld phases; overall, forming liquid-liquid immiscible membranes [30,38,77,78].…”

“…These studies have shown that collective interactions between sterols and saturated lipids induce the formation of condensed 'liquid ordered' (Lo) phases coexisting with 'liquid disordered' (Ld) phases, where the Lo phase displayed slower lateral diffusion. Heterogeneously distributed lipid nanodomains at the plasma membrane of cells, often referred to as rafts, are characterized by a dense lipid lateral packing, nanoscopic enrichment in sterols and saturated acyl chains, a transient lifetime, and a slow internal molecular diffusion [28][29][30]. Several methods have been developed to measure lipid diffusion [11,[31][32][33][34][35][36] to indirectly report on lipid nanodomain formation and protein diffusional hindering [37,38].…”

Lipid Self-Assemblies under the Atomic Force Microscope

“…Furthermore, over the last 50 years, new findings have modified this model towards a greater degree of complexity [3][4][5][6], in which aspects such as protein-protein interactions and lipid leaflet asymmetry have gained importance [7]. Among these relevant novelties, bilayer heterogeneity is perhaps one of the most intriguing, as lipids may be present in different phases and govern the properties of the membrane at different local points [8]. The lipid raft hypothesis has been one of the most impactful contributions to this area [9], leading to the current concept of nanodomains.…”