USE OF SOLID-STATE H-2 NMR FOR STUDYING PROTEIN-LIPID INTERACTIONS ATEMULSION INTERFACES

Interactions between myosin and beta-casein with lipids at lipid-water interfaces were studied by solid-state H-2 NMR using dimyristoylphosp hatidylcholine with the four hydrogens at alpha- and beta-positions (D MPC-d(4)) and the nine protons at the gamma-position substituted by de uterium (DMPC-d(9)). Quadrupole splittings and spin-lattice relaxation times were used to describe the amplitude and rate of molecular motio n of the choline segment, respectively, in liposomes made of pure labe led dimyristoylphosphatidylcholine or admired with non-labeled dimyris toylphosphatidylglycerol (DMPG) in a 1:1 mole ratio. No changes were o bserved in these NMR parameters for the deuterons when increasing amou nts of myosin were added to liposomes exclusively made of DMPC-d(9) or DMPC-d(4). However, when DMPG was present, myosin was found to intera ct electrostatically with the liposomes, and both the quadrupolar spli ttings and spin-lattice relaxation times of all head-group segments we re affected, demonstrating that DMPG was necessary in the liposomes fo r the interaction to occur. The results suggest that positively charge d lysine residues located at the tail domain of myosin provided the ne cessary sites for the lipid-protein interaction, leaving free the head domain for further structural interaction. On the other hand, beta-ca sein was found to interact both with the charged (with DMPG) and neutr al, zwitterionic (DMPC only) liposomes, although this interaction was more pronounced in the charged lipids. In the interaction with charged liposomes, beta-casein was able to affect the lineshape of the NMR sp ectra from DMPC-d(9) deuterons, even at low protein concentration (lip id/protein mole ratio = 30 000:1), indicating its ability to locate at emulsion interfaces. (C) 1997 John Wiley & Sons, Ltd.