Compositions for Protein Labeling Using Lipoic Acid Ligases

The present disclosure provides compositions and methods of use thereof for labeling peptide and proteins in vitro or in vivo. The methods described herein employ lipoic acid ligase or mutants thereof, and lipoic acid analogs (e.g., lipoic acid analogs comprising a resorufin moiety) recognized by lipoic acid ligase and lipoic acid ligase mutants. Also provided herein is a method of imaging protein-protein interaction via a reaction mediated by lipoic acid ligase.