title: Identification of the chromophores involved in aggregation-dependent energy quenching of the monomeric photosystem II antenna protein Lhcb5.
abstract: Non-photochemical quenching (NPQ) of excess absorbed light energy is a fundamental process that regulates photosynthetic light harvesting in higher plants. Among several proposed NPQ mechanisms, aggregation-dependent quenching (ADQ) and charge transfer quenching have received the most attention. In vitro spectroscopic features of both mechanisms correlate with very similar signals detected in more intact systems and in vivo, where full NPQ can be observed. A major difference between the models is the proposed quenching site, which is predominantly the major trimeric light-harvesting complex II in ADQ and exclusively monomeric Lhcb proteins in charge transfer quenching. Here, we studied ADQ in both monomeric and trimeric Lhcb proteins, investigating the activities of each antenna subunit and their dependence on zeaxanthin, a major modulator of NPQ in vivo. We found that monomeric Lhcb proteins undergo stronger quenching than light-harvesting complex II during aggregation and that this is enhanced by binding to zeaxanthin, as occurs during NPQ in vivo. Finally, the analysis of Lhcb5 mutants showed that chlorophyll 612 and 613, in close contact with lutein bound at site L1, are important facilitators of ADQ.
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: Julien
authors.initials: J
authors.lastname: Girardon
authors.forename: Nico
authors.initials: N
authors.lastname: Betterle
authors.forename: Tomas
authors.initials: T
authors.lastname: Morosinotto
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
mesh_terms: D017360:Arabidopsis; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D061146:Chlorophyll Binding Proteins; D004734:Energy Metabolism; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016296:Mutagenesis; D009154:Mutation; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010858:Pigmentation; D055503:Protein Multimerization; D020673:Protein Renaturation; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013997:Time Factors; D024341:Xanthophylls / Q000378:metabolism; D065146:Zeaxanthins
chemical_list: D029681:Arabidopsis Proteins; D061146:Chlorophyll Binding Proteins; C490432:LHCB5 protein, Arabidopsis; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D021122:Protein Subunits; D024341:Xanthophylls; D065146:Zeaxanthins; D002734:Chlorophyll; D000077194:Chlorophyll A