A Biocompatible Condensation Reaction for the Labeling of Terminal Cysteine Residues on Proteins

Going live: A protein-labeling method based on the use of a single amino acid tag—an N-terminal cysteine residue—and small-molecule probes containing a cyanobenzothiazole (CBT) unit has been used for the specific fluorescence labeling of proteins in vitro and at the surface of live cells (see scheme). This simple ligation reaction proceeds with a high degree of specificity under physiological conditions. Rd: a rhodamine dye; TEV: tobacco etch virus.