ANALYSIS OF POLYPEPTIDE BACKBONE T(1) RELAXATION DATA USING AN EXPERIMENTALLY DERIVED MODEL

The time scale of internal motion of the Ala3-Leu4 peptide linkage plane of gramicidin A in its channel conformation is analyzed by interpreting solid-state 15N T1 measurements taken at 4.7 and 9.4 T. The T1 relaxation measurements have been interpreted using a structural model of local motion which has previously been experimentally determined. According to this model, the individual peptide plane motion is a rotational diffusion subject to a harmonic restoring potential about an axis through successive α carbons. The results which best fit the model to the data reported here and to previously determined information about the motions of the gramicidin channel suggest that the correlation time for librations of the Ala3-Leu4 peptide linkage is 36 ns. This suggests that the peptide backbone motions of the gramicidin channel may be on the same time scale as the translational motion of a cation in the channel. © 1993 Academic Press, Inc.