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

Relaxation measurements of side-chain (CH2)-C-13-groups of uniformly C-13 labeled human ubiquitin were performed at 600 MHz and 800 MHz magnetic field strength at 30degreesC. Dipole-dipole cross-correlated relaxation effects in T-1 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 C-13 T-1 relaxation times. Heteronuclear {H-1}-C-13 NOEs obtained by using different proton saturation schemes indicate that the influence of cross-correlation is small. The experimental T-1 and NOE data were interpreted in a model-free way in terms of a generalized order parameter and an internal correlation time.