Protein conformational dynamics studied by 15N and 1H R1ρ relaxation dispersion: Application to wild-type and G53A ubiquitin crystals

Solid-state NMR spectroscopy can provide site-resolved information about protein dynamics over many time scales. Here we combine protein deuteration, fast magic-angle spinning (similar to 45-60 kHz) and proton detection to study dynamics of ubiquitin in microcrystals, and in particular a mutant in a region that undergoes microsecond motions in a beta-turn region in the wild-type protein. We use N-15 R-1 rho relaxation measurements as a function of the radio-frequency (RF) field strength, i.e. relaxation dispersion, to probe how the G53A mutation alters these dynamics. We report a population-inversion of conformational states: the conformation that in the wild-type protein is populated only sparsely becomes the predominant state. We furthermore explore the potential to use amide-H-1 R-1 rho relaxation to obtain insight into dynamics. We show that while quantitative interpretation of H-1 relaxation remains beyond reach under the experimental conditions, due to coherent contributions to decay, one may extract qualitative information about flexibility.