Cell-free synthesis of ¹⁵N-labeled proteins for NMR studies

Modern cell-free in vitro protein synthesis systems present powerful tools for the synthesis of isotope-labeled proteins in high yields. The production of selectively ¹⁵N-labeled proteins from ¹⁵N-labeled amino acids is particularly economic and yields are often sufficient to analyze the proteins very quickly by two-dimensional NMR spectra recorded of the crude reaction mixture without concentration or chromatographic purification of the protein. We review methodological aspects of cell-free in vitro protein synthesis based on an Escherichia coli cell extract, in particular with regard to the production of ¹⁵N-labeled proteins for analysis by NMR spectroscopy.