Production of Isotopically Labeled KRAS4b

Isotopically labelled proteins are important reagents in structural biology as well as in targeted drug development. The field continues to advance with complex multi-isotope labeling. We have combined our experience in high-level soluble KRAS4b expression with protocols for isotope incorporation, to achieve reliable and efficient approaches for several labeling strategies. Typical experiments achieve nearly 100% ¹⁵N incorporation, with yields in the range of 1.3-24.6 mg/L (median = 6.4 mg/L, n = 53). Improvements in the growth parameters in the presence of deuterium reduce the standard time of fermentation from 5 days to 3 days by modifying the medium used during the weaning process. The methods described are compatible with multi-isotope labeling and site-specific labeling.