title: Spectral and functional studies on siphonaxanthin-type light-harvesting complex of photosystem II from Bryopsis corticulans.
abstract: Carotenoids with conjugated carbonyl groups possess special photophysical properties which have been studied in some water-soluble light-harvesting proteins (Polívka and Sundström, Chem Rev 104:2021-2071, 2004). However, siphonaxanthin-type light-harvesting complexes of photosystem II (LHCII) in siphonous green alga have received fewer studies. In the present study, we determined sequences of genes for several Bryopsis corticulans Lhcbm proteins, which showed that they belong to the group of major LHCII and diverged early from green algae and higher plants. Analysis of pigment composition indicated that this siphonaxanthin-type LHCII contained in total 3 siphonaxanthin and siphonein but no lutein and violaxanthin. In addition, 2 chlorophylls a in higher plant LHCII were replaced by chlorophyll b. These changes led to an increased absorption in green and blue-green light region compared with higher plant LHCII. The binding sites for chlorophylls, siphonaxanthin, and siphonein were suggested based on the structural comparison with that of higher plant LHCII. All of the ligands for the chlorophylls were completely conserved, suggesting that the two chlorophylls b were replaced by chlorophyll a without changing their binding sites in higher plant LHCII. Comparisons of the absorption spectra of isolated siphonaxanthin and siphonein in different organic solutions and the effect of heat treatment suggested that these pigments existed in a low hydrophobic protein environment, leading to an enhancement of light harvesting in the green light region. This low hydrophobic protein environment was maintained by the presence of more serine and threonine residues in B. corticulans LHCII. Finally, esterization of siphonein may also contribute to the enhanced harvesting of green light.
authors.affiliation: Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, People's Republic of China.
authors.forename: Wenda
authors.initials: W
authors.lastname: Wang
authors.forename: Xiaochun
authors.initials: X
authors.lastname: Qin
authors.forename: Min
authors.initials: M
authors.lastname: Sang
authors.forename: Dongqin
authors.initials: D
authors.lastname: Chen
authors.forename: Kebin
authors.initials: K
authors.lastname: Wang
authors.forename: Rongchen
authors.initials: R
authors.lastname: Lin
authors.forename: Congming
authors.initials: C
authors.lastname: Lu
authors.forename: Jian-Ren
authors.initials: JR
authors.lastname: Shen
authors.forename: Tingyun
authors.initials: T
authors.lastname: Kuang
mesh_terms: D000042:Absorption; D020418:Algal Proteins / Q000737:chemistry; D000595:Amino Acid Sequence; D002499:Centrifugation, Density Gradient; D000460:Chlorophyta / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D045342:Light-Harvesting Protein Complexes / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D045332:Photosystem II Protein Complex / Q000302:isolation & purification / Q000378:metabolism*; D010802:Phylogeny; D010860:Pigments, Biological / Q000378:metabolism; D016415:Sequence Alignment; D012996:Solutions; D012997:Solvents; D013050:Spectrometry, Fluorescence; D013696:Temperature; D024341:Xanthophylls / Q000378:metabolism*
chemical_list: D020418:Algal Proteins; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D012996:Solutions; D012997:Solvents; D024341:Xanthophylls; C003314:siphonaxanthin