The behaviour of side chains is fundamental to the biology and pathology of proteins. They play essential roles in processes as diverse as folding, catalysis, binding and allosteric regulation, and it is clear that in many cases their function is as much linked to their dynamic behaviour as their structure. Despite their significance, methods probing the behaviour of side chains are limited, and mainly focus on small proteins and residues containing methyl groups.
13C-detected NMR spectroscopy in a per-deuterated environment provides an excellent means of probing residues and systems intractable to conventional 1H-detected methods. The presented suite of pulse sequences make use of a single, uniformly-labelled sample to characterise a range of non-methyl- and methyl-bearing side chains. The base residue-specific carbon-carbon correlation experiment has been extended to include elements reporting on both the structure and dynamic behaviour of these side chains. Chemical exchange saturation transfer (CEST) experiments report on conformational exchange on a millisecond time-scale, whilst long-range 13C-13C scalar couplings report on nanosecond to millisecond motions. Most importantly, these experiments have been used to investigate systems as large as 82 kDa. The presented class of methods promises characterisation of side-chain behaviour in large systems and at a level that has so far been reserved for the protein backbone.
 Pritchard & Hansen 2019 Nature Communications 10:1747