title: Homo-FRET microscopy in living cells to measure monomer-dimer transition of GFP-tagged proteins.
abstract: Fluorescence anisotropy decay microscopy was used to determine, in individual living cells, the spatial monomer-dimer distribution of proteins, as exemplified by herpes simplex virus thymidine kinase (TK) fused to green fluorescent protein (GFP). Accordingly, the fluorescence anisotropy dynamics of two fusion proteins (TK27GFP and TK366GFP) was recorded in the confocal mode by ultra-sensitive time-correlated single-photon counting. This provided a measurement of the rotational time of these proteins, which, by comparing with GFP, allowed the determination of their oligomeric state in both the cytoplasm and the nucleus. It also revealed energy homo-transfer within aggregates that TK366GFP progressively formed. Using a symmetric dimer model, structural parameters were estimated; the mutual orientation of the transition dipoles of the two GFP chromophores, calculated from the residual anisotropy, was 44.6 +/- 1.6 degrees, and the upper intermolecular limit between the two fluorescent tags, calculated from the energy transfer rate, was 70 A. Acquisition of the fluorescence steady-state intensity, lifetime, and anisotropy decay in the same cells, at different times after transfection, indicated that TK366GFP was initially in a monomeric state and then formed dimers that grew into aggregates. Picosecond time-resolved fluorescence anisotropy microscopy opens a promising avenue for obtaining structural information on proteins in individual living cells, even when expression levels are very low.
authors.affiliation: Institut Jacques Monod, Centre National de la Recherche Scientifique, Université P6/P7, 75251 Paris, France.
authors.forename: I
authors.initials: I
authors.lastname: Gautier
authors.forename: M
authors.initials: M
authors.lastname: Tramier
authors.forename: C
authors.initials: C
authors.lastname: Durieux
authors.forename: J
authors.initials: J
authors.lastname: Coppey
authors.forename: R B
authors.initials: RB
authors.lastname: Pansu
authors.forename: J C
authors.initials: JC
authors.lastname: Nicolas
authors.forename: K
authors.initials: K
authors.lastname: Kemnitz
authors.forename: M
authors.initials: M
authors.lastname: Coppey-Moisan
mesh_terms: D000818:Animals; D019556:COS Cells; D002470:Cell Survival; D002522:Chlorocebus aethiops; D019281:Dimerization; D004735:Energy Transfer; D005454:Fluorescence Polarization; D049452:Green Fluorescent Proteins; D008027:Light; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence / Q000379:methods; D020836:Protein Structure, Quaternary; D011993:Recombinant Fusion Proteins / Q000737:chemistry* / Q000378:metabolism*; D012399:Rotation; D018139:Simplexvirus / Q000201:enzymology / Q000235:genetics; D013937:Thymidine Kinase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014709:Vero Cells
chemical_list: D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D013937:Thymidine Kinase