Off-resonance TROSY-selected R 1rho experiment with improved sensitivity for medium- and high-molecular-weight proteins.

NMR spin relaxation techniques that utilize relaxation interference phenomena (TROSY) enable chemical exchange processes to be characterized in high-molecular-weight proteins. A TROSY-selected (TS) approach for measuring off-resonance R1rho relaxation in the spin-locked rotating reference frame is developed using three principles: (i) deuteration of nonexchangeable 1H sites to minimize remote dipole-dipole interactions, (ii) selective excitation of the slowly relaxing 15N doublet component to obtain optimal initial conditions, and (iii) selective inversion of one of the 15N doublet components to suppress cross-relaxation during the spin-lock period. The method is validated using [90%-15N, 70%-2H] ubiquitin at 280 K. The TROSY-selected R1rho experiment enables characterization of backbone dynamics on the microsecond time scale in large proteins.