NMR identification of left‐handed polyproline type II helices

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 ³J_HNα and ¹J_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 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 ³J_HNα and ¹J_CαHα 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