Probing slow protein dynamics by adiabatic R(1rho) and R(2rho) NMR experiments.

Slow micros/ms dynamics involved in protein folding, binding, catalysis, and allostery are currently detected using NMR dispersion experiments such as CPMG (Carr-Purcell-Meiboom-Gill) or spin-lock R(1rho). In these methods, protein dynamics are obtained by analyzing relaxation dispersion curves obtained from either changing the time spacing between 180 degree pulses or by changing the effective spin-locking field strength. In this Communication, we introduce a new method to induce a dispersion of relaxation rates. Our approach relies on altering the shape of the adiabatic full passage pulse and is conceptually different from existing approaches. By changing the nature of the adiabatic radiofrequency irradiation, we are able to obtain rotating frame R(1rho) and R(2rho) dispersion curves that are sensitive to slow micros/ms protein dynamics (demonstrated with ubiquitin). The strengths of this method are to (a) extend the dynamic range of the relaxation dispersion analysis, (b) avoid the need for multiple magnetic field strengths to extract dynamic parameters, (c) measure accurate relaxation rates that are independent of frequency offset, and (d) reduce the stress to NMR hardware (e.g., cryoprobes).