title: Chlorophyll triplet quenching and photoprotection in the higher plant monomeric antenna protein Lhcb5.
abstract: In oxygenic photosynthetic organisms, chlorophyll triplets are harmful excited states readily reacting with molecular oxygen to yield the reactive oxygen species (ROS) singlet oxygen. Carotenoids have a photoprotective role in photosynthetic membranes by preventing photoxidative damage through quenching of chlorophyll singlets and triplets. In this work we used mutation analysis to investigate the architecture of chlorophyll triplet quenching sites within Lhcb5, a monomeric antenna protein of Photosystem II. The carotenoid and chlorophyll triplet formation as well as the production of ROS molecules were studied in a family of recombinant Lhcb5 proteins either with WT sequence, mutated into individual chlorophyll binding residues or refolded in vitro to bind different xanthophyll complements. We observed a site-specific effect in the efficiency of chlorophyll-carotenoid triplet-triplet energy transfer. Thus chlorophyll (Chl) 602 and 603 appear to be particularly important for triplet-triplet energy transfer to the xanthophyll bound into site L2. Surprisingly, mutation on Chl 612, the chlorophyll with the lower energy associated and in close contact with lutein in site L1, had no effect on quenching chlorophyll triplet excited states. Finally, we present evidence for an indirect role of neoxanthin in chlorophyll triplet quenching and show that quenching of both singlet and triplet states is necessary for minimizing singlet oxygen formation.
authors.affiliation: Dipartimento di Biotecnologie, Università di Verona , Ca' Vignal 1, strada le Grazie 15, I-37134 Verona, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Ballottari
authors.forename: Milena
authors.initials: M
authors.lastname: Mozzo
authors.forename: Julien
authors.initials: J
authors.lastname: Girardon
authors.forename: Rainer
authors.initials: R
authors.lastname: Hienerwadel
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
mesh_terms: D017360:Arabidopsis / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002338:Carotenoids / Q000737:chemistry; D002734:Chlorophyll / Q000737:chemistry*; D061146:Chlorophyll Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004735:Energy Transfer; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D026082:Singlet Oxygen / Q000737:chemistry / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D061146:Chlorophyll Binding Proteins; C490432:LHCB5 protein, Arabidopsis; D045332:Photosystem II Protein Complex; D011994:Recombinant Proteins; D002734:Chlorophyll; D026082:Singlet Oxygen; D002338:Carotenoids