Integral membrane proteins in nanodiscs can be studied by solution NMR spectroscopy

We present a two-dimensional solution NMR spectrum of an integral membrane protein (IMP) in a nanodisc. Solution NMR relies on rapid isotropic tumbling of the analyte with correlation times in the nanosecond range. IMPs in a cellular membrane do not satisfy this condition. Previous liquid-state NMR studies on IMPs were conducted in organic solvent or artificial membrane mimicking particles like detergent micelles. Nanodiscs are relatively small (150 kDa), detergent-free model membranes that are suitable for functional reconstitution of IMPs. Nanodiscs allow solubilization of integral membrane proteins in a nearly native lipid bilayer environment. The 70 residue polypeptide CD4mut was incorporated into nanodiscs. CD4mut features one transmembrane helix. The aliphatic (1)H-(13)C HSQC spectrum of nanodiscs with inserted, ((13)C, (15)N)-labeled CD4mut exhibits reasonably dispersed protein and lipid NMR signals. Our results demonstrate that IMPs in nanodiscs are amenable to liquid-state NMR methodology.