Lipid domains in the exoplasmic and cytoplasmic leaflet of the human erythrocyte membrane: a spin label approach

Abstract

The existence of different lipid domains in the monolayers of the human erythrocyte membrane was investigated at 4 degrees C by employing spin-labelled phospholipid analogues. Spectra of analogues located exclusively either in the exoplasmic or in the cytoplasmic leaflet of erythrocyte membranes were recorded. Spectra were simulated by variation of order parameter describing the average amplitude of motion of the long molecular axis of the nitrogen 2 p pi orbital of the spin label and of the respective correlation times. For both leaflets at least three components were required to fit the experimental spectra, differing mainly in the order parameter. While the parameters of each component are not very different between both membrane halves, the relative contribution of each component to the spectrum is different between the exoplasmic and cytoplasmic leaflet. The order parameter of the most fluid component, presumably resembling the lipid bulk phase, is smaller in the cytoplasmic leaflet in comparison to the exoplasmic one. The lateral coexistence of different lipid domains in the human red blood cell membrane is concluded. The molecular nature of those domains is discussed.

Fast and Accurate Characterization of Biological Membranes by EPR Spectral Simulations of Nitroxides

“…The linewidths for spin probes in oriented systems such as liquid crystal systems can be calculated by considering the anisotropic rotational relaxation times (2). According to our experience with membrane spectra composed of several spectral components, the influence of the anisotropic rotational relaxation on the fit becomes small (25). This enables us to describe the rotational dynamics within a particular domain with one effective empirical correlation time c .…”

The role of cholesterol in rod outer segment membranes

“…It has become widely accepted that regions of biological membranes exist which are highly specialized and which are enriched in specific proteins and lipids [88][89][90][91][92][93][94][95][96][97][98][99][100][101][102]. Microdomain organization may be driven by lipid-protein and/or by lipid/lipid interactions.…”

Quantifying the Lateral Lipid Domain Properties in Erythrocyte Ghost Membranes Using EPR-Spectra Decomposition

“…It appears, therefore, that the domain type 2 is somehow stabilized. The special properties of the domain type 2 have been suggested before (6), where the stability of the domain type 2 was explained by its specific phospholipid composition. Another possibility could be that the domains contributing to the domain type 2 are associated with some of the erythrocytes' supra-molecular structure, like embedded proteins.…”

“…We will not deal with the question of how the domain structure arises, e.g., whether it is a consequence of lipid-lipid interactions or lipid-protein interactions (5). Also, we will not address the problem of the difference between the domain structure of the exoplasmic and the cytoplasmic membrane leaflets (6).…”

“…But lately, with the upgrade to the heterogeneous picture of membrane structure, experimental approaches are able to provide a description of the local fluidity characteristics. Different experimental methods show the coexistence of domains; these methods include EPR, nuclear magnetic resonance, neutron diffraction, fluorescence methods, single-particle tracking, atomic force microscopy, and Raman spectroscopy (see reviews (4,5,8) and (6,(9)(10)(11)(12)(13)). The lateral lipid domains are thought to play an important role in some biological processes.…”