Fig. 1. (a) Molecular structures of the fluorogenic probes FCANB and AcFCANB. (b) No-wash live cell imaging of protein labeling with AcFCANB and MBP (top) and MBP–PYP (bottom) expressed in HEK 293T cells. Scale bar: 10 μm. (c) Schematic illustration for the mechanism of labeling acceleration. (d) Structure of PYP showing the reactive Cys-69 surrounded by the four acidic residues targeted for mutation.