Site‐Specific Anchoring a Luminescent Tag in a Protein with Non‐Emissive Iridium(III) Complex

Abstract

AbstractSite‐specific modification of proteins with synthetic fluorescent tag effectively improves the resolution of imaging, and such a labeling method with negligible three‐dimensional structural perturbations and minimal impact on the biological functions of proteins is of high interest to dissect the high‐resolution activities of biomolecules in complex systems. To this end, several non‐emissive iridium(III) complexes [Ir(C−N)2(H2O)2]+OTF− (C−N denotes various cyclometalated ligands) were designed and synthesized. These complexes were tested for attaching a protein by coordinating to H/X (HisMet, HisHis, and HisCys) that are separated by i and i+4 in α‐helix. Replacement of the two labile water ligands in the iridium(III) complex by a protein HisHis pair increases the luminescent intensity up to over 100 folds. This labeling approach has been demonstrated in a highly specific and efficient manner in a number of proteins, and it is also feasible for labeling target proteins in cell lysates.