Synthesis of a 13C-methylene-labeled isoleucine precursor as a useful tool for studying protein side-chain interactions and dynamics

In this study, we present the synthesis and incorporation of a metabolic isoleucine precursor compound for selective methylene labeling. The utility of this novel alpha-ketoacid isotopologue is shown by incorporation into the protein Brd4-BD1, which regulates gene expression by binding to acetylated histones. High quality single quantum C-13-(1) H-HSQC were obtained, as well as triple quantum HTQC spectra, which are superior in terms of significantly increased C-13-T-2 times. Additionally, large chemical shift perturbations upon ligand binding were observed. Our study thus proves the great sensitivity of this precursor as a reporter for side-chain dynamic studies and for investigations of CH-pi interactions in protein-ligand complexes.