NMR identification of left‐handed polyproline type II helices

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Abstract
NMR characteristics of a model left-handed 31-helical peptide are reported in this study. With temperature and sequence corrections on the predicted random coil 15N chemical shifts, a significant 15N chemical shift deviation is observed for the model 31 peptide. The 15N chemical shift differences also correlate well with the molar ellipticities (at 220 nm) of the CD spectra at different temperatures, indicating that the 15N chemical shift is a sensitive probe for 31-helices. The average 3JHNα and 1JCαHα values of the model peptide are determined to be 6.5 and 142.6 Hz, respectively, which are consistent with the values calculated from the geometry of 31-helices. With careful measurements of amide 15N chemical shifts and incorporating temperature and sequence effect corrections, the 15N chemical shifts can be used together with 3JHNα and 1JCαHα to differentiate 31-helices from random coils with high confidence. Based on the observed NMR characteristics, a strategy is developed for probing left-handed 31-helical structures from other secondary structures. © 2003 Wiley Periodicals, Inc. Biopolymers 69: 270–281, 2003