Photooxidative stress-inducible orange and pink water-soluble astaxanthin-binding proteins in eukaryotic microalga

• Published in: Communications biology Vol. 3; no. 1; p. 490
• Main Authors: Kawasaki, Shinji, Yamazaki, Keita, Nishikata, Tohya, Ishige, Taichiro, Toyoshima, Hiroki, Miyata, Ami
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 07.09.2020; Nature Publishing Group
• Subjects: 14/19; 38/39; 45/91; 631/449/2667; 631/449/2686; 82/81; 82/83; Algae; Algal Proteins - chemistry; Algal Proteins - isolation & purification; Algal Proteins - metabolism; Amino Acid Sequence; Antioxidants; Astaxanthin; Biology; Biomedical and Life Sciences; Carrier Proteins - chemistry; Carrier Proteins - isolation & purification; Carrier Proteins - metabolism; Color; Free Radical Scavengers - metabolism; Glycosylation; Glycosylphosphatidylinositol; Isoelectric points; Life Sciences; Light; Microalgae - metabolism; Oxidative Stress - radiation effects; Proteins; PTEN-induced putative kinase; Scenedesmus; Scenedesmus - metabolism; Singlet Oxygen - metabolism; Solubility; Solutions; Water - chemistry; Xanthophylls - metabolism
• ISSN: 2399-3642; 2399-3642
• DOI: 10.1038/s42003-020-01206-7

Lipid astaxanthin, a potent antioxidant known as a natural sunscreen, accumulates in eukaryotic microalgae and confers photoprotection. We previously identified a photooxidative stress-inducible water-soluble astaxanthin-binding carotenoprotein (AstaP) in a eukaryotic microalga ( Coelastrella astaxanthina Ki-4) isolated from an extreme environment. The distribution in eukaryotic microalgae remains unknown. Here we identified three novel AstaP orthologs in a eukaryotic microalga, Scenedesmus sp. Oki-4N. The purified proteins, named AstaP-orange2, AstaP-pink1, and AstaP-pink2, were identified as secreted fasciclin proteins with potent 1 O 2 quenching activity in aqueous solution, which are characteristics shared with Ki-4 AstaP. Nonetheless, the absence of glycosylation in the AstaP-pinks, the presence of a glycosylphosphatidylinositol (GPI) anchor motif in AstaP-orange2, and highly acidic isoelectric points (pI = 3.6–4.7), differed significantly from that of AstaP-orange1 (pI = 10.5). These results provide unique examples on the use of water-soluble forms of astaxanthin in photosynthetic organisms as novel strategies for protecting single cells against severe photooxidative stresses. Kawasaki et al. identified three water-soluble astaxanthin binding proteins (AstaP) orthologs, AstaP-orange2, AstaP-pink1, and AstaP-pink2, in the eukaryotic microalga Scenedesmus sp. Oki-4N, grown under stress conditions. Their detailed characterisation showed that each AstaP ortholog had a specific absorption feature, but all were capable of quenching single oxygen. They envision that AstaP accumulation might have protective functions against photooxidative stress.