Microsecond Protein Dynamics from Combined Bloch-McConnell and Near-Rotary-Resonance R1p Relaxation-Dispersion MAS NMR

Studying protein dynamics on microsecond‐to‐millisecond time scales can provide important insight into protein function. In magic‐angle‐spinning (MAS) NMR, microsecond dynamics can be visualized by R1rho rotating‐frame relaxation dispersion experiments in different regimes of radio‐frequency field strengths: at low RF field strength, isotropic‐chemical‐shift fluctuation leads to "Bloch‐McConnell‐type" relaxation dispersion, while when the RF field approaches resonance conditions with the MAS frequency ("Near‐Rotary‐Resonance Relaxation Dispersion", NERRD), bond angle fluctuations become visible through the dipolar/CSA reorientation. Here we explore the joint analysis of both regimes to gain comprehensive insight into motion in terms of geometric amplitudes, chemical‐shift changes, populations and exchange kinetics. We use a numerical simulation procedure to illustrate these effects and apply the methodology to gain insight into a previously described conformational exchange process in microcrystalline ubiquitin.