A clickable glutamine (CliQ) derivative for the traceless reversible modification of peptides and proteins.

The Cu(I)-mediated click reaction of proteins with affinity tags enables their selective isolation from complex mixtures. However, irreversible protein modification limits the interpretation of results from subsequent biophysical and biochemical assays. We report a facile and modular chemical strategy to reversibly modify peptides and proteins with biotin and FLAG affinity tags at a clickable glutamine (CliQ) residue.