Chapter 3: Protein Backbone and Side-chain ¹⁵N Spin Relaxation Techniques to Study Biomacromolecular Interactions

Biomacromolecular dynamics studies based on ¹⁵N spin relaxation are well established among the atomic-level structural biology techniques, accessing molecular mobility at a wide range of time scales spanning over ten orders of magnitude. The ¹⁵N labelling constitutes the simplest, most accessible, stable isotope labelling strategy for numerous proteins and nucleic acids. Therefore, it has become a convenient method to experimentally target the atomic and sub-atomic levels of molecular mobility. Here we present the currently available experimental techniques to access the dynamics of the protein backbone and side-chains, and the numerical methods of interpretation. The complexity of molecular motional models has led to separate measurements and interpretation of the dynamics for well-folded globular proteins and domains, highly dynamic, flexible, intrinsically disordered regions, and entirely flexible, intrinsically disordered proteins. In addition, separate approaches have been developed to detect and interpret the mobility of various amino acid side-chains. The advantages and limitations of the available tools and the emerging need for a more in-depth understanding of molecular functional dynamics are discussed.