Backbone dynamics of polycrystalline peptides studied by measurements of 15N NMR lineshapes and 13C transverse relaxation times

Backbone dynamics of small peptides containing GlyGly residues were examined by analyzing the N-15 NMR line shapes and the C-13 relaxation times of some static polycrystalline samples. Anisotropy of the N-15 chemical shift tensor of the amide nitrogen in GlyGly was determined by spectral simulation of the observed N-15 chemical shift and N-15-H-1 dipolar-chemical shift powder patterns. It was found that by lowering temperature from 40 degrees C to -120 degrees C, the delta(11) and delta(22) values shifted to low and high field by 2.5 ppm, respectively, while the delta(33) value was unchanged. The observed displacement of the principal values of the N-15 chemical shift tensor was interpreted by taking librational motions with small amplitudes into account. This librational motion was interpreted in terms of a two-site jump model about the delta(33) axis that is very close to the C alpha C alpha' direction of the peptides with a jump angle of 17 degrees, as manifested from the simulated spectra. The correlation time of the librational motion of the peptide plane was estimated to be 2.3 x 10(-4) s at room temperature by analysing C-13 T-2 values in the presence of a H-1 decoupling field of 50 kHz. (C) 1998 Elsevier Science B.V.