title: Conformationally locked chromophores as models of excited-state proton transfer in fluorescent proteins.
abstract: Members of the green fluorescent protein (GFP) family form chromophores by modifications of three internal amino acid residues. Previously, many key characteristics of chromophores were studied using model compounds. However, no studies of intermolecular excited-state proton transfer (ESPT) with GFP-like synthetic chromophores have been performed because they either are nonfluorescent or lack an ionizable OH group. In this paper we report the synthesis and photochemical study of two highly fluorescent GFP chromophore analogues: p-HOBDI-BF2 and p-HOPyDI:Zn. Among known fluorescent compounds, p-HOBDI-BF(2) is the closest analogue of the native GFP chromophore. These irrreversibly (p-HOBDI-BF(2)) and reversibly (p-HOPyDI:Zn) locked compounds are the first examples of fully planar GFP chromophores, in which photoisomerization-induced deactivation is suppressed and protolytic photodissociation is observed. The photophysical behavior of p-HOBDI-BF2 and p-HOPyDI:Zn (excited state pK(a)'s, solvatochromism, kinetics, and thermodynamics of proton transfer) reveals their high photoacidity, which makes them good models of intermolecular ESPT in fluorescent proteins. Moreover, p-HOPyDI:Zn is a first example of "super" photoacidity in metal-organic complexes.
authors.affiliation: Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya 16/10, 117997 Moscow, Russia.
authors.forename: Mikhail S
authors.initials: MS
authors.lastname: Baranov
authors.forename: Konstantin A
authors.initials: KA
authors.lastname: Lukyanov
authors.forename: Alexandra O
authors.initials: AO
authors.lastname: Borissova
authors.forename: Jordan
authors.initials: J
authors.lastname: Shamir
authors.forename: Dmytro
authors.initials: D
authors.lastname: Kosenkov
authors.forename: Lyudmila V
authors.initials: LV
authors.lastname: Slipchenko
authors.forename: Laren M
authors.initials: LM
authors.lastname: Tolbert
authors.forename: Ilia V
authors.initials: IV
authors.lastname: Yampolsky
authors.forename: Kyril M
authors.initials: KM
authors.lastname: Solntsev
mesh_terms: D003116:Color; D049452:Green Fluorescent Proteins / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry; D011487:Protein Conformation; D011522:Protons; D013050:Spectrometry, Fluorescence; D015032:Zinc / Q000737:chemistry
chemical_list: D007093:Imidazoles; D011522:Protons; D049452:Green Fluorescent Proteins; C029899:imidazole; D015032:Zinc