Cross-correlation suppressed T1 and NOE experiments for protein side-chain 13CH2 groups.

Relaxation measurements of side-chain 13CH2-groups of uniformly 13C labeled human ubiquitin were performed at 600 MHz and 800 MHz magnetic field strength at 30 degrees C. Dipole-dipole cross-correlated relaxation effects in T1 experiments were suppressed by the combination of radio-frequency pulses and pulsed field gradients during the relaxation delay leading to monoexponential relaxation decays that allow a more accurate extraction of the 13C T1 relaxation times. Heteronuclear [1H]-13C NOEs obtained by using different proton saturation schemes indicate that the influence of cross-correlation is small. The experimental T1 and NOE data were interpreted in a model-free way in terms of a generalized order parameter and an internal correlation time.