title: A novel astaxanthin-binding photooxidative stress-inducible aqueous carotenoprotein from a eukaryotic microalga isolated from asphalt in midsummer.
abstract: Water-soluble orange carotenoid proteins (OCPs) that bind 3'-hydroxyechinenone are found in cyanobacteria, and are thought to play a key role in photoprotection. The distribution of OCPs in eukaryotes remains largely unknown. In this study, we identified a novel OCP that predominantly binds astaxanthin from a eukaryotic microalga, strain Ki-4, isolated from a dry surface of heated asphalt in midsummer. A purified astaxanthin-binding OCP, named AstaP, shows high solubility in water with an absorption peak at 484 nm, and possesses a heat-stable activity that quenches singlet oxygen. The deduced amino acid sequence of AstaP comprises an N-terminal hydrophobic signal peptide, fasciclin domains found in secreted and cell surface proteins, and N-linked glycosylation sites, the first example of a carotenoprotein among fasciclin family proteins. AstaP homologs of unknown function are distributed mainly in organisms from the hydrosphere, such as marine bacteria, cyanobacteria, sea anemone and eukaryotic microalgae; however, AstaP exhibits a unique extraordinarily high isoelectric point (pI) value among homologs. The gene encoding AstaP, as well as the AstaP peptide, is expressed abundantly under conditions of dehydration and salt stress in conjunction with high light exposure. As a unique aqueous carotenoprotein, AstaP will provide a novel function of OCPs in protection against extreme photooxidative stresses.
authors.affiliation: Department of Biosciences, Tokyo University of Agriculture, Setagaya-ku, Tokyo, 156-8502 Japan. kawashin@nodai.ac.jp
authors.forename: Shinji
authors.initials: S
authors.lastname: Kawasaki
authors.forename: Keisuke
authors.initials: K
authors.lastname: Mizuguchi
authors.forename: Masaru
authors.initials: M
authors.lastname: Sato
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Kono
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Shimizu
mesh_terms: D020418:Algal Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D015152:Blotting, Northern; D002338:Carotenoids / Q000378:metabolism; D000460:Chlorophyta / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D005057:Eukaryotic Cells / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects / Q000528:radiation effects; D006838:Hydrocarbons; D008027:Light; D013058:Mass Spectrometry / Q000379:methods; D058086:Microalgae / Q000166:cytology / Q000302:isolation & purification / Q000378:metabolism*; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D018384:Oxidative Stress / Q000528:radiation effects; D010802:Phylogeny; D011485:Protein Binding; D012621:Seasons; D017386:Sequence Homology, Amino Acid; D012965:Sodium Chloride / Q000494:pharmacology; D012995:Solubility; D014867:Water / Q000378:metabolism; D024341:Xanthophylls / Q000378:metabolism
chemical_list: D020418:Algal Proteins; D006838:Hydrocarbons; D024341:Xanthophylls; D014867:Water; D002338:Carotenoids; D012965:Sodium Chloride; C006647:asphalt; C005948:astaxanthine
keywords: Astaxanthin; Carotenoid; Fasciclin; Microalgae; Photooxidative stress; Singlet oxygen