Microsecond Dynamics in Ubiquitin Probed by Solid-State 15N NMR Spectroscopy R1ρ Relaxation Experiments under Fast MAS (60-110 kHz)

N-15 R-1 rho relaxation experiments in solid-state NMR spectroscopy are sensitive to timescales and amplitudes of internal protein motions in the hundreds of nano-to microsecond time window, which is difficult to probe by solution-state NMR spectroscopy. By using N-15 R-1 rho relaxation experiments, a simplified approach to detect low microsecond protein dynamics is described and residue-specific correlation times are determined from the ratio of N-15 R-1 rho rate constants at different magic angle spinning frequencies. Micro-crystalline ubiquitin exhibits small-amplitude dynamics on a timescale of about 1 mu s across the entire protein, and larger amplitude motions, also on the 1 mu s timescale, for several sites, including the beta(1)-beta(2) turn and the N terminus of the a helix. According to the analysis, the microsecond protein backbone dynamics are of lower amplitude than that concluded in previous solid-state NMR spectroscopy studies, but persist across the entire protein with a rather uniform timescale of 1 mu s.