Bilayered mixed micelles or bicelles are magnetically anisotropic, self-assembling model membrane structures comprised of long-chain phospholipids and short-chain detergent molecules. In the most widely accepted model of this system, the bicelle is discoid in shape, with the short-chain DHPC molecules aggregating to form rims around long-chain DMPC bilayers. While this model is consistent with most NMR and scattering data (X-ray and neutron), it inadequately describes the liquid-crystalline behavior of bicelle solutions at temperatures where magnetic alignment occurs. Temperature plays a central role in the structure of lipid aggregates, and the impact of temperature on bicelles has not been studied as extensively as composition and concentration. Therefore, a series of fluorescence probe and resonance energy transfer (FRET) measurements of labeled bicelle solutions as a function of temperature were conducted to monitor lipid mixing as an indication of bicelle structure and aggregation. The results of these measurements are not consistent with the large-scale changes in lipid mixing with temperature that have been attributed to bicelle solutions in other studies. The spectral data indicate that there is reorganization within mixed lipid aggregates as a function of temperature and bilayer fusion. In an attempt to reconcile these data with physical data and the theory of liquid-crystalline behavior, the authors speculate that the structure of bicelles is an interconnected network of DMPC bilayers interrupted by DHPC rimmed pores at elevated temperatures.

No abstract