Live‐Cell Protein Sulfonylation Based on Proximity‐driven N‐Sulfonyl Pyridone Chemistry

The development of bioorthogonal approaches for labeling of endogenous proteins under the multimolecular crowding conditions of live cells is highly desirable for the analysis and engineering of proteins without using genetic manipulation. N‐Sulfonyl pyridone (SP) is reported as a new reactive group for protein sulfonylation. The ligand‐directed SP chemistry was able to modify not only purified proteins in vitro, but also endogenous ones on the surface of and inside live cells selectively and rapidly, which allowed to convert endogenous proteins to FRET‐based biosensors in situ. Ligand‐directed N‐sulfonyl pyridone chemistry afforded the specific sulfonylation of endogenous proteins without disturbing their original nature. This chemical strategy allowed the simple conversion of endogenous proteins in live cell habitats into semisynthetic FRET biosensors for the analysis of the dynamic process in protein–ligand (small molecule) interactions.