title: The Cation-π Interaction Enables a Halo-Tag Fluorogenic Probe for Fast No-Wash Live Cell Imaging and Gel-Free Protein Quantification.
abstract: The design of fluorogenic probes for a Halo tag is highly desirable but challenging. Previous work achieved this goal by controlling the chemical switch of spirolactones upon the covalent conjugation between the Halo tag and probes or by incorporating a "channel dye" into the substrate binding tunnel of the Halo tag. In this work, we have developed a novel class of Halo-tag fluorogenic probes that are derived from solvatochromic fluorophores. The optimal probe, harboring a benzothiadiazole scaffold, exhibits a 1000-fold fluorescence enhancement upon reaction with the Halo tag. Structural, computational, and biochemical studies reveal that the benzene ring of a tryptophan residue engages in a cation-π interaction with the dimethylamino electron-donating group of the benzothiadiazole fluorophore in its excited state. We further demonstrate using noncanonical fluorinated tryptophan that the cation-π interaction directly contributes to the fluorogenicity of the benzothiadiazole fluorophore. Mechanistically, this interaction could contribute to the fluorogenicity by promoting the excited-state charge separation and inhibiting the twisting motion of the dimethylamino group, both leading to an enhanced fluorogenicity. Finally, we demonstrate the utility of the probe in no-wash direct imaging of Halo-tagged proteins in live cells. In addition, the fluorogenic nature of the probe enables a gel-free quantification of fusion proteins expressed in mammalian cells, an application that was not possible with previously nonfluorogenic Halo-tag probes. The unique mechanism revealed by this work suggests that incorporation of an excited-state cation-π interaction could be a feasible strategy for enhancing the optical performance of fluorophores and fluorogenic sensors.
authors.forename: Yu
authors.identifier: 0000-0002-0779-1488
authors.initials: Y
authors.lastname: Liu
authors.forename: Kun
authors.initials: K
authors.lastname: Miao
authors.forename: Noah P
authors.initials: NP
authors.lastname: Dunham
authors.affiliation: Department of Chemistry, University of Washington , Seattle, Washington 98105, United States.
authors.forename: Hongbin
authors.initials: H
authors.lastname: Liu
authors.forename: Matthew
authors.initials: M
authors.lastname: Fares
authors.forename: Amie K
authors.identifier: 0000-0002-1234-8472
authors.initials: AK
authors.lastname: Boal
authors.affiliation: Department of Chemistry, University of Washington , Seattle, Washington 98105, United States.
authors.forename: Xiaosong
authors.identifier: 0000-0001-7341-6240
authors.initials: X
authors.lastname: Li
authors.forename: Xin
authors.identifier: 0000-0001-6686-1645
authors.initials: X
authors.lastname: Zhang
mesh_terms: D002412:Cations; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005456:Fluorescent Dyes / Q000737:chemistry*; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D006867:Hydrolases / Q000235:genetics* / Q000378:metabolism; D007700:Kinetics; D057054:Molecular Imaging / Q000379:methods*; D015335:Molecular Probes / Q000737:chemistry*; D010957:Plasmids / Q000737:chemistry / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics* / Q000378:metabolism; D013194:Staining and Labeling / Q000379:methods; D013830:Thiadiazoles / Q000737:chemistry*; D014162:Transfection; D014364:Tryptophan / Q000737:chemistry
chemical_list: D002412:Cations; D005456:Fluorescent Dyes; D015335:Molecular Probes; D011993:Recombinant Fusion Proteins; D013830:Thiadiazoles; C015700:benzo-1,2,3-thiadiazole; D014364:Tryptophan; D006867:Hydrolases; C046137:haloalkane dehalogenase