Use of Selective Trp Side Chain Labeling To Characterize Protein−Protein and Protein−Ligand Interactions by NMR Spectroscopy

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Abstract
Recent studies on amino acid occurrence in protein binding sites suggest that only a reduced number of residues are responsible for most interaction energy in protein−protein and protein−ligand interactions. Above all, tryptophan (Trp) seems to be the most frequent residue in protein's hot spots. Here we report a novel, efficient, and cost-effective method to selectively incorporate specific isotope labels into the side chains of Trp residues in recombinant proteins. We show that the method proposed allows selective NMR observation of Trp side chains that enables studies of ligand binding, protein−protein interactions, hydrogen binding, protein folding, and side chain dynamics. Examples with the protein BIR3 will be given.