The best of both worlds: A new lipid complex has micelle and bicelle-like properties

Abstract

Bicelles have been demonstrated to be a valuable tool for studying membrane protein interactions and structure in vitro. They are distinguished by a distinct lipid bilayer that mimics the plasma membrane of cells making it more native-like than its detergent micelle counter-part. Bicelles are typically comprised of a long-chain phospholipid such as dimyristoylphosphatidylcholine (DMPC) and a short-chain phospholipid such as dihexanoylphosphatidylcholine (DHPC). When mixed together in solution DMPC-DHPC bicelles assume a discoidal structure comprised of a heterogeneous arrangement where the short-chain lipids gather around the rim of the disk and the long-chain lipids form the flat, planar, bilayer region. In this study, the nonionic surfactant, C₈E₅, was used to prepare mixtures with DMPC to determine if it adopts properties similar to bicelles with a q ≥ 0.5. At q ≥ 0.5, DMPC-DHPC bicelles are bilayered and DMPC is sequestered from the detergent micelle-like DHPC. Mixtures of DMPC and C₈E₅ were prepared at various q values, a parameter used to describe the mole ratio of DMPC to DHPC in the preparation of bicelles. Employing biophysical methods like dynamic light scattering, ³¹P-NMR and analytical ultracentrifugation, properties of these lipid-detergent complexes are described. Interestingly they adopted a spherical-shaped micellar structure morphology and did not assume a discoidal shape typical of bicelles at q ≥ 0.5. However, they appear to retain bilayer-like properties that may prove beneficial for in vitro biophysical studies of membrane proteins.