title: Proton transfer events in GFP.
abstract: Proton transfer is one of the most important elementary processes in biology. Green fluorescent protein (GFP) serves as an important model system to elucidate the mechanistic details of this reaction, because in GFP proton transfer can be induced by light absorption. Illumination initiates proton transfer through a 'proton-wire', formed by the chromophore (the proton donor), water molecule W22, Ser205 and Glu222 (the acceptor), on a picosecond time scale. To obtain a more refined view of this process, we have used a combined approach of time resolved mid-infrared spectroscopy and visible pump-dump-probe spectroscopy to resolve with atomic resolution how and how fast protons move through this wire. Our results indicate that absorption of light by GFP induces in 3 ps (10 ps in D(2)O) a shift of the equilibrium positions of all protons in the H-bonded network, leading to a partial protonation of Glu222 and to a so-called low barrier hydrogen bond (LBHB) for the chromophore's proton, giving rise to dual emission at 475 and 508 nm. This state is followed by a repositioning of the protons on the wire in 10 ps (80 ps in D(2)O), ultimately forming the fully deprotonated chromophore and protonated Glu222.
authors.affiliation: Department of Physics and Astronomy, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands. didonato@lens.unifi.it
authors.forename: Mariangela
authors.initials: M
authors.lastname: Di Donato
authors.forename: Luuk J G W
authors.initials: LJ
authors.lastname: van Wilderen
authors.forename: Ivo H M
authors.initials: IH
authors.lastname: Van Stokkum
authors.forename: Thomas Cohen
authors.initials: TC
authors.lastname: Stuart
authors.forename: John T M
authors.initials: JT
authors.lastname: Kennis
authors.forename: Klaas J
authors.initials: KJ
authors.lastname: Hellingwerf
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
authors.forename: Marie Louise
authors.initials: ML
authors.lastname: Groot
mesh_terms: D017666:Deuterium Oxide / Q000737:chemistry; D049452:Green Fluorescent Proteins / Q000737:chemistry* / Q000378:metabolism; D006860:Hydrogen Bonding; D007700:Kinetics; D011522:Protons; D013055:Spectrophotometry, Infrared
chemical_list: D011522:Protons; D049452:Green Fluorescent Proteins; D017666:Deuterium Oxide