INTERACTION OF A TYPE-II MYOSIN WITH BIOLOGICAL-MEMBRANES STUDIED BY H-2 SOLID-STATE NMR

Deuterium nuclear magnetic resonance spectroscopy (H-2 NMR) has been e mployed 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 deutera ted at its headgroup by substituting the four protons at the alpha- an d beta-positions (DMPC-d(4)) and the nine protons at the gamma-positio n (DMPC-d(9)). DMPG was perdeuterated at its headgroup (DMPG-d(5)). No changes were observed in the quadrupole splittings or spin-lattice re laxation times for the deuterated DMPC headgroup segments when increas ing amounts of myosin were added to liposomes, made exclusively of DMP C-d(9) or of DMPC-d(4). However, upon the insertion of the negatively charged lipid DMPG at 1:1 molar ratio into the DMPC bilayers, myosin w as found to interact electrostatically with the liposomes, thereby aff ecting significantly both the quadrupole splittings and spin-lattice r elaxation rates of the alpha-, beta-, and gamma-deuterons in labeled D MPC. Monitoring DMPG-d(5) in mixed DMPC/DMPG bilayers revealed a direc t 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+ we re complexed to the head domain of myosin, a reduced interaction with the negatively charged bilayers was observed. The results clearly indi cate that a type II myosin can interact with membranes without the nee d for a specific hydrophobic domain or an anchor in the protein molecu le, provided that negatively charged lipids are present in the bilayer .