title: Triplet-triplet energy transfer in fucoxanthin-chlorophyll protein from diatom Cyclotella meneghiniana: insights into the structure of the complex.
abstract: Although the major light harvesting complexes of diatoms, called FCPs (fucoxanthin chlorophyll a/c binding proteins), are related to the cab proteins of higher plants, the structures of these light harvesting protein complexes are much less characterized. Here, a structural/functional model for the "core" of FCP, based on the sequence homology with LHCII, in which two fucoxanthins replace the central luteins and act as quenchers of the Chl a triplet states, is proposed. Combining the information obtained by time-resolved EPR spectroscopy on the triplet states populated under illumination, with quantum mechanical calculations, we discuss the chlorophyll triplet quenching in terms of the geometry of the chlorophyll-carotenoid pairs participating to the process. The results show that local structural rearrangements occur in FCP, with respect to LHCII, in the photoprotective site.
authors.affiliation: Department of Chemical Sciences, University of Padua, via Marzolo 1, 35131 Padova, Italy.
authors.forename: Marilena
authors.initials: M
authors.lastname: Di Valentin
authors.forename: Elena
authors.initials: E
authors.lastname: Meneghin
authors.forename: Laura
authors.initials: L
authors.lastname: Orian
authors.forename: Antonino
authors.initials: A
authors.lastname: Polimeno
authors.forename: Claudia
authors.initials: C
authors.lastname: Büchel
authors.forename: Enrico
authors.initials: E
authors.lastname: Salvadori
authors.forename: Christopher W M
authors.initials: CW
authors.lastname: Kay
authors.forename: Donatella
authors.initials: D
authors.lastname: Carbonera
mesh_terms: D002734:Chlorophyll / Q000378:metabolism*; D000077194:Chlorophyll A; D061146:Chlorophyll Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D017377:Diatoms / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004735:Energy Transfer; D008027:Light; D024341:Xanthophylls / Q000378:metabolism*
chemical_list: D061146:Chlorophyll Binding Proteins; D024341:Xanthophylls; C025164:fucoxanthin; D002734:Chlorophyll; D000077194:Chlorophyll A
keywords: Car; Carotenoid; Chl; DFT; Density Functional Theory; EPR; ESE; Electron Spin Echo; FCP; Fucoxanthin; Fx; ISC; LHCII; ODMR; Optically Detected Magnetic Resonance; PCP; QM/QM; TR-EPR; TTET; Time Resolved Electron Paramagnetic Resonance; Triplet state; ZFS; carotenoid; chlorophyll; fucoxanthin; fucoxanthin chlorophyll protein; intersystem crossing; light harvesting complex II; peridinin–chlorophyll–protein; quantum mechanics/quantum mechanics; triplet–triplet energy transfer; zero field splitting