Interaction of a type II myosin with biological membranes studied by 2H solid state NMR.

Deuterium nuclear magnetic resonance spectroscopy (2H NMR) has been employed to investigate the interaction of lung type II myosin protein with neutral bilayers containing dimyristoylphosphatidylcholine (DMPC) as the only constituent and mixed bilayers containing the negatively charged lipid dimyristoylphosphatidylglycerol (DMPG). DMPC was deuterated at its headgroup by substituting the four protons at the alpha- and beta-positions (DMPC-d4) and the nine protons at the gamma-position (DMPC-d9). DMPG was perdeuterated at its headgroup (DMPG-d5). No changes were observed in the quadrupole splittings or spin-lattice relaxation times for the deuterated DMPC headgroup segments when increasing amounts of myosin were added to liposomes, made exclusively of DMPC-d9 or of DMPC-d4. However, upon the insertion of the negatively charged lipid DMPG at 1:1 molar ratio into the DMPC bilayers, myosin was found to interact electrostatically with the liposomes, thereby affecting significantly both the quadrupole splittings and spin-lattice relaxation rates of the alpha-, beta-, and gamma-deuterons in labeled DMPC. Monitoring DMPG-d5 in mixed DMPC/DMPG bilayers revealed a direct electrostatic interaction of DMPG with the protein, where positively charged lysine residues located at the tail domain of myosin provide the necessary sites for the interaction to occur. When ATP and Mg2+ were complexed to the head domain of myosin, a reduced interaction with the negatively charged bilayers was observed. The results clearly indicate that a type II myosin can interact with membranes without the need for a specific hydrophobic domain or an anchor in the protein molecule, provided that negatively charged lipids are present in the bilayer.