Accurately probing slow motions on millisecond timescales with a robust NMR relaxation experiment

A new pulse scheme is proposed for the accurate measurement of relaxation dispersion, which cycles the phases of CPMG pulses. Numerical simulations show that systematic errors in the measured relaxation rates mainly result from off-resonance and radio frequency inhomogeneity effects and they can be significantly suppressed with the method proposed here. The method has been demonstrated on human liver fatty acid binding protein. It allows the reliable identification of residues undergoing conformational exchange on millisecond timescales and accurate extraction of kinetics parameters. The relaxation dispersion data indicate that human liver fatty acid binding protein is highly flexible on millisecond timescales.