NMR assignment method for amide signals with cell-free protein synthesis system.

Nuclear magnetic resonance (NMR) methods are widely used to determine the three-dimensional structures of proteins, to estimate protein folding, and to discover high-affinity ligands for proteins. However, one of the problems to apply such NMR methods to proteins is that we should obtain mg quantities of (15)N and/or (13)C labeled pure proteins of interest. Here, we describe the method to produce dual amino acid-selective (13)C-(15)N labeled proteins for NMR study using the improved wheat germ cell-free system, which enables sequence-specific assignments of amide signals simply even for very large protein.