Blue fluorescent protein analogs as chemosensors for Zn2+

Three chemosensors for Zn2+ were designed and synthesized based on the chromophore of the blue fluorescent protein (BFP). Among them, IMMPI (4-((1H-imidazol-2-yl)methylene)-1-methyl-2-phenyl-1H-imidazol-5(4H)-one) contained one BFP chromophore unit, which sequestered Zn2+ with nitrogen in the two imidazole rings, while Di-IMMPI-a and Di-IMMPI-o contained two IMMPI units that were connected together using an alkane and a methoxy chain, respectively. All three molecules selectively interacted with Zn2+ with a 1:1 mode. Di-IMMPI-a had a dissociation constant <0.03 μM for Zn2+, more than 30 folds stronger than that of IMMPI. The fluorescences of IMMPI, Di-IMMPI-a, and Di-IMMPI-o were turned on upon the binding of Zn2+, accompanied by the quantum yields enhancing from <0.002 to 0.352, 0.451, and 0.194, respectively. Fluorescence images showed that Di-IMMPI-a responded to Zn2+ in cell cytosol. Our work demonstrated the potentiality for the development of practical Zn2+ sensors based on the isolated BFP chromophores without the proteinframe.

► Three chemosensors for Zn2+ were designed based on the chromophore of BFP.
► IMMPI contains two imidazole rings as the chromophore of BFP.
► Di-IMMPI-a and Di-IMMPI-o contain two IMMPI units.
► IMMPIs (IMMPI, Di-IMMPI-a and Di-IMMPI-o) bound to Zn2+ with high affinity and selectivity.
► Di-IMMPI-a is the most sensitive fluorescent Zn2+ chemosensor based on GFP and its derivatives at present.