title: Distance measurements in peridinin-chlorophyll a-protein by light-induced PELDOR spectroscopy. Analysis of triplet state localization.
abstract: Triplet-triplet energy transfer from chlorophylls to carotenoids is the mechanism underlying the photoprotective role played by carotenoids in many light harvesting complexes, during photosynthesis. The peridinin-chlorophyll-a protein (PCP) is a water-soluble light harvesting protein of the dinoflagellate Amphidinium carterae, employing peridinin as the main carotenoid to fulfil this function. The dipolar coupling of the triplet state of peridinin, populated under light excitation in isolated PCP, to the MTSSL nitroxide, introduced in the protein by site-directed mutagenesis followed by spin labeling, has been measured by Pulse ELectron-electron DOuble Resonance (PELDOR) spectroscopy. The triplet-nitroxide distance derived by this kind of experiments, performed for the first time in a protein system, allowed the assignment of the triplet state to a specific peridinin molecule belonging to the pigment cluster. The analysis strongly suggests that this peridinin is the one in close contact with the water ligand to the chlorophyll a, thus supporting previous evidences based on ENDOR and time resolved-EPR.
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35131 Padova, Italy.
authors.forename: Marilena
authors.initials: M
authors.lastname: Di Valentin
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35131 Padova, Italy.
authors.forename: Maria Giulia
authors.initials: MG
authors.lastname: Dal Farra
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35131 Padova, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Galazzo
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35131 Padova, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Albertini
authors.affiliation: Biophysics, Department of Biology and Biotechnology, Ruhr-University Bochum, D-44780 Bochum, Germany.
authors.forename: Tim
authors.initials: T
authors.lastname: Schulte
authors.affiliation: Biophysics, Department of Biology and Biotechnology, Ruhr-University Bochum, D-44780 Bochum, Germany.
authors.forename: Eckhard
authors.initials: E
authors.lastname: Hofmann
authors.affiliation: Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35131 Padova, Italy. Electronic address: donatella.carbonera@unipd.it.
authors.forename: Donatella
authors.initials: D
authors.lastname: Carbonera
mesh_terms: D002338:Carotenoids / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects*; D004578:Electron Spin Resonance Spectroscopy; D004735:Energy Transfer; D008024:Ligands; D008027:Light; D008958:Models, Molecular; D010788:Photosynthesis / Q000528:radiation effects*; D011485:Protein Binding; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects*; D013113:Spin Labels; D013329:Structure-Activity Relationship; D014867:Water / Q000737:chemistry / Q000378:metabolism
chemical_list: D008024:Ligands; D015800:Protozoan Proteins; D013113:Spin Labels; C073227:peridinin chlorophyll-a protein, Dinophyceae; D014867:Water; D002338:Carotenoids
keywords: Carotenoid; PCP; PELDOR; Peridinin; Pulse EPR; Triplet state