title: Investigating State Restriction in Fluorescent Protein FRET Using Time-Resolved Fluorescence and Anisotropy.
abstract: Most fluorescent proteins exhibit multiexponential fluorescence decays, indicating a heterogeneous excited state population. FRET between fluorescent proteins should therefore involve multiple energy transfer pathways. We recently demonstrated the FRET pathways between EGFP and mCherry (mC), upon the dimerization of 3-phosphoinositide dependent protein kinase 1 (PDK1), to be highly restricted. A mechanism for FRET restriction based on a highly unfavorable κ2orientation factor arising from differences in donor-acceptor transition dipole moment angles in a far from coplanar and near static interaction geometry was proposed. Here this is tested via FRET to mC arising from the association of glutathione (GSH) and glutathione S-transferase (GST) with an intrinsically homogeneous and more mobile donor Oregon Green 488 (OG). A new analysis of the acceptor window intensity, based on the turnover point of the sensitized fluorescence, is combined with donor window intensity and anisotropy measurements which show that unrestricted FRET to mC takes place. However, a long-lived anisotropy decay component in the donor window reveals a GST-GSH population in which FRET does not occur, explaining previous discrepancies between quantitative FRET measurements of GST-GSH association and their accepted values. This reinforces the importance of the local donor-acceptor environment in mediating energy transfer and the need to perform spectrally resolved intensity and anisotropy decay measurements in the accurate quantification of fluorescent protein FRET.
authors.affiliation: Department of Physics & Astronomy, Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, and Department of Cell & Developmental Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom; Department of Physics & Astronomy, Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, and Department of Cell & Developmental Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom; Department of Physics & Astronomy, Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, and Department of Cell & Developmental Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Blacker
authors.affiliation: Department of Chemical Engineering and Biotechnology, University of Cambridge , Pembroke Street, Cambridge CB2 3RA, United Kingdom.
authors.forename: WeiYue
authors.initials: W
authors.lastname: Chen
authors.affiliation: Cambridge Institute for Medical Research, University of Cambridge , Cambridge CB2 0XY, United Kingdom.
authors.forename: Edward
authors.initials: E
authors.lastname: Avezov
authors.affiliation: Department of Physics & Astronomy, Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, and Department of Cell & Developmental Biology, University College London , Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Marsh
authors.affiliation: Department of Physics & Astronomy, Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, and Department of Cell & Developmental Biology, University College London , Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Duchen
authors.affiliation: Department of Chemical Engineering and Biotechnology, University of Cambridge , Pembroke Street, Cambridge CB2 3RA, United Kingdom.
authors.forename: Clemens F
authors.initials: CF
authors.lastname: Kaminski
authors.affiliation: Department of Physics & Astronomy, Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, and Department of Cell & Developmental Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom; Department of Physics & Astronomy, Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, and Department of Cell & Developmental Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Angus J
authors.initials: AJ
authors.lastname: Bain