Discovery of a Fluorogenic Probe for In Situ Pyruvate Kinase M2 Isoform (PKM2) Labeling through Chemoselective S_NAr with a Binding Site Lysine Residue

The key challenge of developing reaction-based turn-on probes is to establish latent electrophilic fluorophores exhibiting high reactivity only upon binding to a specific protein(s). Herein, we identified such a fluorophore, 6-arylthioether-substituted 3-cyano-1-oxo-1H-phenalene-2-carboxylate, which chemoselectively labels binding site Cys or Lys residues. Based on this fluorophore, we developed the first reaction-based turn-on pyruvate kinase M2 isoform (PKM2) fluorescent probe AT-OPC1, which selectively labels PKM2 with the binding site Lys305. The latent electrophilic reactivity of the fluorophore endows the probe with precise detection of the expression of PKM2 in situ by means of both in-gel fluorescence imaging at the proteome level and real-time no-wash cell imaging approaches, which has the potential to be applied in cancer diagnoses.