NMR RELAXATION AND PROTEIN MOBILITY

The increased availability of isotope-enriched proteins and the high s ensitivity of proton-detected heteronuclear experiments have stimulate d studies of protein mobility via N-15 and C-13 relaxation. Developmen ts during the past few years include new pulse sequences that yield mo re reliable values for relaxation rates, and pulse sequences that enab le the measurement of new types of relaxation parameters. Methods with which to map distribution functions of motional frequencies (spectral density functions) from combinations of relaxation parameters have be en suggested. Extensive measurements of N-15 and C-13 relaxation param eters have been made for a number of proteins and interpreted on the b asis of the so-called 'model-free' approach; often, active sites of pr oteins are found to be mobile. In a few cases, molecular dynamics simu lations have been carried out to simulate relaxation parameters.