Dynamics of β-CH and β-CH2 groups of amino acid side chains in proteins

The dynamics of amino acid side chains of uniformly C-13/N-15-enriched ribonuclease T1 (RNase T1) have been investigated. Heteronuclear longitudinal relaxation rates, H-1/C-13 NOEs, and transverse cross-correlated cross-relaxation rates between the S-x and the (SxIzIz2)-I-1 operators (SIIS cross relaxation) [Ernst and Ernst (1993) J. Magn. Reson., A110, 202-213] have been determined in this study. New pulse sequences for measuring the longitudinal relaxation time and the heteronuclear NOE of aliphatic side chain carbon nuclei were developed using the CCONH type of magnetization transfer and H-1(N) detection. In addition, an improved pulse sequence for the determination of the SIIS cross relaxation is presented. For the analysis of the relaxation rates, the model of restricted rotational diffusion around the chi(1) dihedral angle has been applied [London and Avitabile (1978) J. Am. Chern. Sec., 100, 7159-7165]. These techniques were used in order to describe the side chain dynamics of the small globular protein RNase T1 (104 amino acids, MW about 11 kDa). Qualitative values of microdynamical parameters were obtained for 73 out of 85 amino acid side chains (glycine and alanine residues excepted) whereas more quantitative values were derived for 67 beta-CH and beta-CH2 groups.