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

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.