As therapeutic proteins gain importance alongside traditional small molecule drugs, there is increasing interest in using NMR methods to examine their structure, dynamics, and stability/aggregation in solution.
Modern heteronuclear NMR of proteins relies on isotopically-labeled samples containing NMR active nuclei in the peptide backbone, sidechains, or both.
Although isotopic-labeling of recombinant protein is typically carried out in E. Coli expression systems, many biotherapeutic proteins must be expressed in eukaryotic systems to insure proper folding and/or post-translational modifications. In practice, this means overexpression in either yeast, insect or mammalian cells.
Increased interest in attaining labeled protein samples for analysis by NMR is leading to better commercial availability of isotopically-labeled expression media and improved vectors for overexpression in non-bacterial systems.
Comprehensive reviews of state-of-the-art protocols and procedures for expression of isotopically-labeled proteins in non-standard systems are available here: yeast, insect cells, and mammalian cells.