ABSTRACT
ABSTRACT Molecular torsion angles in peptides and proteins encode important secondary structure (backbone) and tertiary structure (side-chain) information. Solidstate nuclear magnetic resonance spectroscopy is a powerful tool for determining these torsion angles because of the inherent orientation dependence of nuclear spin interactions. This review summarizes the large number of techniques developed in
the last decade for determining molecular torsion angles. Techniques are available for both non-spinning biopolymers, from which exquisite angular resolution can be obtained, and for magic-angle spinning samples, from which high site resolution is available to yield multiple torsion angles in complex proteins. Many of these techniques rely on correlating two spin interaction tensors across the torsion bond of interest and extracting the torsion angle from the sum and difference frequencies of the two interactions. The other techniques measure distances between two nuclei separated by three bonds or more.
