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Molecular mobility of polypeptides containing proline as determined by 13C magnetic resonance

The molecular conformations and dynamics of poly(L‐prolyl), poly(hydroxyl‐L‐prolyl), poly(L‐prolyl‐glycyl), poly(hydroxyl‐L‐prolyl), and poly(glycyl‐glycyl‐L‐prolyl‐glycyl), in aqueous solution, have been studied using 13C pulse Fourier transform nmr spectroscopy. From a measurement of the intensities of major and minor resonances in the spectra of the copolypeptides, it was determined that 15–20% of the glycyl‐prolyl and glycyl‐hydroxyprolyl peptide bonds are cis. Effective rotational correlation times (τeff), obtained from measurements of spin‐lattice relaxation times (T1) of individual backbone and side‐chain carbons, demonstrated that backbone reorientation is approximately isotropic for the five polypeptides and is characterized by correlation times of ca. 0.3–0.6 nanoseconds as a result of rapid segmental motion. In a given polypeptide glycyl and pyrrolidine residues were found to have the same backbone correlation times, but backbone carbon τeff values did decrease as the glycyl content of the peptides increased. A semi‐quantitative analysis of Cβ, Cγ, and Cδ correlation times suggests that rapid ring motion in both prolyl and hydroxyprolyl involves primarily Cγ and Cβ, with the prolyl ring being more mobile than the hydroxyprolyl ring.