Sparse Labeling for Protein NMR

It is standard practice to enrich proteins to high levels of 13C enrichment in-order to make spectral assignments and to ultimately determine structure. However, a high level of uniform 13C enrichment creates scalar and dipolar coupling between the directly bonded 13C nuclei, which for dipolar-based sequences used in solid state NMR, creates large signals which often obscures low-intensity, information-rich signals produced from long range coupling. For scalar-based sequences used in solution state NMR, the presence of directly bonded 13C nuclei will degrade spectral resolution and provides an unwanted dipolar relaxation mechanism for the alpha carbon.

Reduction of 13C-13C dipolar coupling is made possible by sparse 13C labeling. 13C sparse labeling is where the expressed protein does not contain adjacent 13C nuclei. This can be accomplished to a large degree by using selectively 13C-labeled carbon sources for the protein expression. There are several different substrates available for 13C sparse labeling, including glucose, glycerol, and pyruvate.

Related Resources

Stable Isotopes for Biomolecular NMR

Frequently Asked Questions

What is sparse labeling, and how does it help? In sparse labeling, only a random fraction of the carbon atoms in the protein are labeled. This helps solid-state experiments because it removes strong, one-bond couplings (i.e., two 13C atoms next to each other), which give rise to large peaks that obscure smaller, long-range couplings (more helpful in obtaining structural information). 2-13C and 1,3-13C2 glycerols are the most popular carbon source; 1-13C and 2-13C glucose are also popular.

What types of media can be used in sparse labeling? Only E. coli and yeast cells can be used.

Example References

Robson, S.A.; Takeuchi, K.; Boeszoermenyi, A.; et al. 2018. Mixed pyruvate labeling enables backbone resonance assignment of large proteins using a single experiment. Nat Commun, 9(1), 356-366. PMID: 29367739
Loquet, A.; Giller, K.; Becker, S.; et al. 2010. Supramolecular interactions probed by 13C-13C solid-state NMR spectroscopy. J Am Chem Soc, 132, 15164-15166. PMID: 20932028
Wylie, B.J.; Schwieters, C.D.; Oldfield, E.; et al. 2009. Protein structure refinement using 13Cα chemical shift tensors. J Am Chem Soc, 131(3), 985-992. PMID: 19123862