Counterintuitive method improves yields of isotopically labelled proteins expressed in flask-cultured Escherichia coli

NMR is a powerful tool for the structural and dynamic study of proteins. One of the necessary conditions for the study of these proteins is their isotopic labelling with ¹⁵N and ¹³C. One of the most widely used methods to obtain these labelled proteins is heterologous expression of the proteins in E. coli using ¹³C-D-glucose and ¹⁵NH₄Cl as the sole nutrient sources. In recent years, the price of ¹³C-D-glucose has almost tripled, making it essential to develop labelling methods that are as cost effective as possible. In this work, different parameters were studied to achieve the most rational use of ¹³C-D-glucose, and an optimized method was developed to obtain labelled proteins with high labelling and low ¹³C-D-glucose consumption. Surprisingly, the optimized method is also simple and does not require monitoring of culture growth.