Measurement of cross correlation between dipolar coupling and chemical shift anisotropy in the spin relaxation of 13C, 15N-Labeled proteins

We present a simple method for extracting interference effects between chemical shift anisotropy (CSA) and dipolar coupling from spin relaxation measurements in macromolecules, and we apply this method to extracting cross-correlation rates involving interference of amide N-15 CSA and N-15-H-1 dipolar coupling and interference of carbonyl C-13' CSA and N-15-C-13' dipolar coupling, in a small protein. A theoretical basis for the interpretation of these rates is presented, While it proves difficult to quantitatively separate the structural and dynamic contributions to these crosscorrelation rates in the presence of anisotropic overall tumbling and a nonaxially symmetric chemical shift tensor, some useful qualitative correlations of data with protein structure can be seen when simplifying assumptions are made. (C) 1998 Academic Press.