Microsecond Dynamics in Ubiquitin Probed by Solid-State ~(15)N NMR Spectroscopy R_(1ρ) Relaxation Experiments under Fast MAS (60-110 kHz)

摘要

~(15)N R_(1ρ)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 solutionstate NMR spectroscopy. By using ~(15)N R_(1ρ)relaxation experiments, a simplified approach to detect low microsecond protein dynamics is described and residue-specific correlation times are determined from the ratio of ~(15)N R_(1ρ)rate constants at different magic angle spinning frequencies. Microcrystalline ubiquitin exhibits small-amplitude dynamics on a timescale of about 1 ms across the entire protein, and larger amplitude motions, also on the 1 ms timescale, for several sites, including the β_1-β_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 μs.