NMR identification of left‐handed polyproline type II helices

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