High-resolution 31P field cycling NMR as a probe of phospholipid dynamics

We have used high-resolution field-cycling P-31 NMR spectroscopy to measure spin-lattice relaxation rates (R-1 = 1/T-1) of multicomponent phospholipid vesicle and micelle samples over a large field range, from 0.1 to 11.7 T. The shape of the curve for R, as a function of field and a model-free analysis were used to extract tau(c), a correlation time for each type of phospholipid molecule in the bilayer that is likely to reflect rotation of the molecule about the axis perpendicular to the membrane surface; S-c(2), a chemical shift anisotropy (CSA) order parameter; and tau(hf), a time constant reflecting faster internal motion. This P-31 technique was also used to monitor association of a peripheral membrane protein, Bacillus thuringiensis phosphatidylinositol-specific phospholipase C, with both phosphaticlylcholine and phosphatidylmethanol bilayers. Differences in phospholipid dynamics induced by the protein shed light on how zwitterionic phosphatidylcholine, and not the anionic phosphaticlylmethanol, activates the enzyme toward its substrate.