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.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Figures have been re-ordered and re-numbered to improve the flow of the paper. The detergent, DDM, was removed from Figure 1. The original Figure 3 was removed. Two tables have been added, Table 1 and 2. The NMR Figure 4 has been reformatted along with Figure 7 - modeling of the lipid complexes. Wording has been changed slightly, i.e. “aggregates” are now called “complexes.” Additional insights and clarification has been added to the interpretation of the light scattering and NMR data. A more in depth discussion of the bicelle parameter, q, has been included. A sizable paragraph detailing the description of sedimentation equilibrium, analytical ultracentrifugation in the introduction has been removed and rewritten to be more concise with less emphasis on the AUC experiment. The title has been changed to better reflect the major findings of the work. The second author has been respectfully removed and is no longer an active participant/collaborator on the work. This person has expressed no further interest in pursuing it.
Abbreviations
- DMPC
- 1,2-dimyristoyl-sn-glycero-3-phosphocholine
- DHPC
- 1,2-dihexanoyl-sn-glycero-3-phosphocholine
- C8E5
- n-octylpentaoxyethylene
- NBD-DMPE
- (1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) (ammonium salt))
- 31P-NMR
- phosphorus nuclear magnetic resonance spectroscopy
- D2O
- deuterium oxide
- CHAPS
- 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate
- CHAPSO
- 3-([3-Cholamidopropyl]dimethylammonio)-2-hydroxy-1-propanesulfonate
- HEPES
- 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid
- DLS
- dynamic light scattering