title: Excitation dynamics and structural implication of the stress-related complex LHCSR3 from the green alga Chlamydomonas reinhardtii.
abstract: LHCSR3 is a member of the Light-Harvesting Complexes (LHC) family, which is mainly composed of pigment-protein complexes responsible for collecting photons during the first steps of photosynthesis. Unlike related LHCs, LHCSR3 is expressed in stress conditions and has been shown to be essential for the fast component of photoprotection, non-photochemical quenching (NPQ), in the green alga Chlamydomonas reinhardtii. In plants, which do not possess LHCSR homologs, NPQ is triggered by the PSBS protein. Both PSBS and LHCSR3 possess the ability to sense pH changes but, unlike PSBS, LHCSR3 binds multiple pigments. In this work we have analyzed the properties of the pigments bound to LHCSR3 and their excited state dynamics. The data show efficient excitation energy transfer between pigments with rates similar to those observed for the other LHCs. Application of an exciton model based on a template of LHCII, the most abundant LHC, satisfactorily explains the collected steady state and time-resolved spectroscopic data, indicating that LHCSR3 has a LHC-like molecular architecture, although it probably binds less pigments. The model suggests that most of the chlorophylls have similar energy and interactions as in LHCII. The most striking difference is the localization of the lowest energy state, which is not on the Chlorophyll a (Chl a) 610-611-612 triplet as in all the LHCB antennas, but on Chl a613, which is located close to the lumen and to the pH-sensing region of the protein.
authors.affiliation: Department of Physics and Astronomy and Institute for Lasers, Life and Biophotonics, Faculty of Sciences, VU University Amsterdam, De Boelelaan, 1081, 1081, HV, Amsterdam, The Netherlands.
authors.forename: Nicoletta
authors.initials: N
authors.lastname: Liguori
authors.affiliation: A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Leninskie Gory, 119992, Moscow, Russia.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Novoderezhkin
authors.affiliation: Department of Physics and Astronomy and Institute for Lasers, Life and Biophotonics, Faculty of Sciences, VU University Amsterdam, De Boelelaan, 1081, 1081, HV, Amsterdam, The Netherlands.
authors.forename: Laura M
authors.initials: LM
authors.lastname: Roy
authors.affiliation: Department of Physics and Astronomy and Institute for Lasers, Life and Biophotonics, Faculty of Sciences, VU University Amsterdam, De Boelelaan, 1081, 1081, HV, Amsterdam, The Netherlands.
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
authors.affiliation: Department of Physics and Astronomy and Institute for Lasers, Life and Biophotonics, Faculty of Sciences, VU University Amsterdam, De Boelelaan, 1081, 1081, HV, Amsterdam, The Netherlands. Electronic address: r.croce@vu.nl.
authors.forename: Roberta
authors.initials: R
authors.lastname: Croce
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000737:chemistry*; D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry
chemical_list: D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A
keywords: Chlamydomonas reinhardtii; LHCSR3; Light-Harvesting Complex; Redfield model; transient absorption