title: Unraveling ultrafast photoinduced proton transfer dynamics in a fluorescent protein biosensor for Ca(2+) imaging.
abstract: Imaging Ca(2+) dynamics in living systems holds great potential to advance neuroscience and cellular biology. G-GECO1.1 is an intensiometric fluorescent protein Ca(2+) biosensor with a Thr-Tyr-Gly chromophore. The protonated chromophore emits green upon photoexcitation via excited-state proton transfer (ESPT). Upon Ca(2+) binding, a significant population of the chromophores becomes deprotonated. It remains elusive how the chromophore structurally evolves prior to and during ESPT, and how it is affected by Ca(2+) . We use femtosecond stimulated Raman spectroscopy to dissect ESPT in both the Ca(2+) -free and bound states. The protein chromophores exhibit a sub-200 fs vibrational frequency shift due to coherent small-scale proton motions. After wavepackets move out of the Franck-Condon region, ESPT gets faster in the Ca(2+) -bound protein, indicative of the formation of a more hydrophilic environment. These results reveal the governing structure-function relationship of Ca(2+) -sensing protein biosensors.
authors.affiliation: Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003 (USA).
authors.forename: Longteng
authors.initials: L
authors.lastname: Tang
authors.forename: Weimin
authors.initials: W
authors.lastname: Liu
authors.forename: Yanli
authors.initials: Y
authors.lastname: Wang
authors.forename: Yongxin
authors.initials: Y
authors.lastname: Zhao
authors.forename: Breland G
authors.initials: BG
authors.lastname: Oscar
authors.forename: Robert E
authors.initials: RE
authors.lastname: Campbell
authors.forename: Chong
authors.initials: C
authors.lastname: Fang
mesh_terms: D002118:Calcium / Q000737:chemistry*; D049452:Green Fluorescent Proteins / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D055668:Photochemical Processes; D011522:Protons
chemical_list: D011522:Protons; D049452:Green Fluorescent Proteins; D002118:Calcium
keywords: calcium ion sensing; excited state proton transport; femtochemistry; fluorescent probes; vibrational spectroscopy