title: Structural and functional analysis of the antiparallel strands in the lumenal loop of the major light-harvesting chlorophyll a/b complex of photosystem II (LHCIIb) by site-directed mutagenesis.
abstract: The light-harvesting chlorophyll a/b-binding protein of photosystem II (LHCIIb) fulfills multiple functions, such as light harvesting and energy dissipation under different illuminations. The crystal structure of LHCIIb at the near atomic resolution reveals an antiparallel strands structure in the lumenal loop between the transmembrane helices B/C. To study the structural and functional significances of this structure, three amino acids (Val-119, His-120, and Ser-123) in this region have been exchanged to Phe, Leu, and Gly, respectively, and the influence of the mutagenesis on the structure and function of LHCIIb has been investigated. The results are as follows. 1) Circular dichroism spectra of the mutations reveals that the antiparallel strands in the lumenal region are very important for adjusting pigment conformation in the neoxanthin domain of LHCIIb. Although the mutagenesis causes only a slight loss of the Neo binding in the complexes (V119F, 0.09; S123G, 0.19; and H120L, 0.27), it imparts remarkable changes to the pigment conformation. 2) Substituting Ser-123 with Gly results in a higher susceptibility to photodamage, an increased tendency to aggregate, and enhanced fluorescence quenching induced by the medium acidification. These results demonstrate that this antiparallel strands domain plays an important role in regulating the pigment conformation and in adjusting the aggregation and the fluorescence yield of LHCIIb.
authors.affiliation: Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Beijing, 100093, China, the; Graduate University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Liu
authors.affiliation: Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Beijing, 100093, China, the; Graduate University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Yajie
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: College of Chemistry, South China University of Technology, Guangzhou 510640, China.
authors.forename: Derong
authors.initials: D
authors.lastname: Cao
authors.affiliation: College of Life Sciences, Capital Normal University, Beijing 100037, China.
authors.forename: Yikun
authors.initials: Y
authors.lastname: He
authors.affiliation: Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Beijing, 100093, China, the; College of Life Sciences, Capital Normal University, Beijing 100037, China.
authors.forename: Tingyun
authors.initials: T
authors.lastname: Kuang
authors.affiliation: Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Beijing, 100093, China, the; Institut für Allgemeine Botanik, Johannes-Gutenberg-Universität Mainz, D-55099 Mainz, Germany. Electronic address: yangch@ibcas.ac.cn.
authors.forename: Chunhong
authors.initials: C
authors.lastname: Yang
mesh_terms: D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D000077194:Chlorophyll A; D002942:Circular Dichroism; D005453:Fluorescence; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed / Q000379:methods*; D009154:Mutation; D018532:Pisum sativum / Q000378:metabolism; D038761:Photobleaching; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A