Solid-state NMR spectroscopy of 10% 13C labeled ubiquitin: spectral simplification and stereospecific assignment of isopropyl groups.

We describe the simplification of 13C-13C correlation spectra obtained from a microcrystalline protein sample expressed on a growth medium of 10% fully 13C labeled glucose diluted in 90% natural abundance glucose as compared to a fully labeled sample. Such a labeling scheme facilitates the backbone and side-chain resonance assignment of Phe, Tyr, His, Asp, Asn, Ile, Lys and Pro and yields an unambiguous stereospecific assignment of the valine Cgamma1, Cgamma2 13C resonances and of Leucine Cdelta2.