CPMG relaxation dispersion.

NMR relaxation is sensitive to molecular and internal motion of proteins. (15)N longitudinal relaxation rate (R 1), transverse relaxation rate (R 2), and {(1)H}-(15)N Nuclear Overhauser Effect (NOE) experiments are often performed to globally elucidate protein dynamics, primarily on the sub-nanosecond timescale. In contrast, constant relaxation time R 2 dispersion experiments are applied to characterize protein equilibrium conformations that interconvert on the millisecond timescale. Information on local conformational equilibria of proteins provides important insights about protein energy landscapes and is useful to interpret molecular recognition mechanisms as well. Here, we describe a protocol for performing (15)N Carr-Purcell-Meiboom-Gill (CPMG) R 2 dispersion measurements in solution, including protein preparation, step-by-step experimental parameter settings, and the first step of data analysis.