A simple method to measure 13CH2 heteronuclear dipolar cross-correlation spectral densities

times in the Here, we report a method to simultaneously determine CH2 cross-correlation spectral densities and T-1 relaxation laboratory and rotating frames. To accomplish this, we have employed an indirect approach that is based on measurement of differences in relaxation rates acquired with and without cross-correlation terms. The new method, which can be employed using multidimensional NMR and standard relaxation pulse sequences, is validated experimentally by investigation of a selectively C-13-enriched hexadecapeptide and the uniformly C-13-enriched immunoglobulin-binding domain of streptococcal protein G (GB1). Use of this approach makes determination of CH2 cross-correlation spectral densities in uniformly C-13-enriched proteins now routine and provides novel information concerning their internal motions. (C) 2004 Elsevier Inc. All rights reserved.