Façade detergents as bicelle rim-forming agents for solution NMR spectroscopy

Out of all membrane mimetics available for solution nuclear magnetic resonance (NMR) spectroscopy, phospholipid bicelles are the most prospective. Unlike lipid-protein nanodiscs their size can be easily controlled over a wide range, and the exchange of matter between the particles can take place. However, recent studies revealed several major drawbacks of conventional 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) and DMPC/3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) bicelles. First, size of such bicelles can increase dramatically upon heating, and, second, rim-forming detergents of bicelles can cause improper folding of the water-soluble globular domains of membrane proteins. In order to avoid these effects, we tested the Façade detergents as possible alternative rim-forming agents for small isotropic bicelles. In the present work we characterized the size of bicelles formed by 3α-hydroxy-7α,12α-di-((O-β-D-maltosyl)-2-hydroxyethoxy)-cholane (Façade-EM) and 3α-hydroxy-7α,12α-di-(((2-(trimethylamino)ethyl)phosphoryl)ethyloxy)-cholane Façade-EPC as a function of temperature and lipid/detergent ratio by 1H NMR diffusion spectroscopy. Additionally, the denaturing effects of these two rim-forming agents were investigated using the junction of the transmembrane and intracellular domains of the p75 neurotrophin receptor (p75NTR) as a model object. We show that the use of Façades allows decreasing the temperature-dependent growth of bicelles. The ability of Façade-EM-based bicelles to support the native structure and soluble state of the p75NTR intracellular domain was also revealed.