The inter-monomer interface of the major light-harvesting chlorophyll a/b complexes of photosystem II (LHCII) influences the chlorophyll triplet distribution.
Under strong light conditions, long-lived chlorophyll triplets ((3)Chls) are formed, which can sensitize singlet oxygen, a species harmful to the photosynthetic apparatus of plants. Plants have developed multiple photoprotective mechanisms to quench (3)Chl and scavenge singlet oxygen in order to sustain the photosynthetic activities. The lumenal loop of light-harvesting chlorophyll a/b complex of photosystem II (LHCII) plays important roles in regulating the pigment conformation and energy dissipation. In this study, site-directed mutagenesis analysis was applied to investigate triplet-triplet energy transfer and quenching of (3)Chl in LHCII. We mutated the amino acid at site 123 located in this region to Gly, Pro, Gln, Thr and Tyr, respectively, and recorded fluorescence excitation spectra, triplet-minus-singlet (TmS) spectra and kinetics of carotenoid triplet decay for wild type and all the mutants. A red-shift was evident in the TmS spectra of the mutants S123T and S123P, and all of the mutants except S123Y showed a decrease in the triplet energy transfer efficiency. We propose, on the basis of the available structural information, that these phenomena are related to the involvement, due to conformational changes in the lumenal region, of a long-wavelength lutein (Lut2) involved in quenching (3)Chl.
Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Lei
L
Zhang
Department of Physics, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
Thor Bernt
TB
Melø
Department of Physics, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
Heng
H
Li
Department of Physics, Norwegian University of Science and Technology, 7491 Trondheim, Norway. Electronic address: razi.naqvi@ntnu.no.
K Razi
KR
Naqvi
Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China. Electronic address: yangch@ibcas.ac.cn.
Chunhong
C
Yang
D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D000077194:Chlorophyll A; D002942:Circular Dichroism; D004735:Energy Transfer; D005453:Fluorescence; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014975:Lutein / Q000378:metabolism; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D018532:Pisum sativum / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D038761:Photobleaching; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding
D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C037184:chlorophyll b; D014975:Lutein; D000077194:Chlorophyll A
Chlorophyll triplet; Conformation; Light-harvesting chlorophyll a/b complexes; Lutein; Mutagenesis