Determination of Torsion Angles in Proteins and Peptides Using Solid State NMR

A combination of Solid State NMR (SSNMR) dipolar recoupling and double quantum CSA−CSA correlation experiments are used to determine the Ramachandran angles φ and ι in a crystalline tripeptide (AGG) and a 14 amino acid peptide designed to be helical. The advantage of the SSNMR approach described herein is the ability to measure both φ and ψ to high resolution using a single noncrystalline, doubly carbonyl labeled peptide. It is also shown that DRAWS and DQDRAWS data are insensitive to 14 N− 13 C and 15 N− 13 C dipolar couplings making corrections for these effects unnecessary. Extremes in secondary structure (e.g., α-helix vs β-sheet) can be discerned by simple inspection of DQDRAWS spectra. Subtleties in secondary structure (α-helix vs 3 10 -helix) can be distinguished by simulation of the DQDRAWS spectrum.