title: Utilization of light by fucoxanthin-chlorophyll-binding protein in a marine centric diatom, Chaetoceros gracilis.
abstract: The major light-harvesting pigment protein complex (fucoxanthin-chlorophyll-binding protein complex; FCP) was purified from a marine centric diatom, Chaetoceros gracilis, by mild solubilization followed by sucrose density gradient centrifugation, and then characterized. The dynamic light scattering measurement showed unimodality, indicating that the complex was highly purified. The amount of chlorophyll a (Chl a) bound to the purified FCP accounted for more than 60 % of total cellular Chl a. The complex was composed of three abundant polypeptides, although there are nearly 30 FCP-related genes. The two major components were identified as Fcp3 (Lhcf3)- and Fcp4 (Lhcf4)-equivalent proteins based on their internal amino acid sequences and a two-dimensional isoelectric focusing electrophoresis analysis developed in this work. Compared with the thylakoids, the FCP complex showed higher contents of fucoxanthin and chlorophyll c but lower contents of the xanthophyll cycle pigments diadinoxanthin and diatoxanthin. Fluorescence excitation spectra analyses indicated that light harvesting, rather than photosystem protection, is the major function of the purified FCP complex, which is associated with more than 60 % of total cellular Chl a. These findings suggest that the huge amount of Chl bound to the FCP complex composed of Lhcf3, Lhcf4, and an unidentified minor protein has a light-harvesting function to allow efficient photosynthesis under the dim-light conditions in the ocean.
authors.affiliation: Department of Life Science, Graduate School of Life Science, University of Hyogo, 3-2-1 Kohto, Kamigohri, Ako-gun, Hyogo, 678-1297, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Ishihara
authors.affiliation: Graduate School of Biostudies, Kyoto University, Kyoto, 606-8502, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Ifuku
authors.affiliation: Institute of Protein Research, Osaka University, Suita, Osaka, 565-0871, Japan.
authors.forename: Eiki
authors.initials: E
authors.lastname: Yamashita
authors.affiliation: Department of Life Science, Graduate School of Life Science, University of Hyogo, 3-2-1 Kohto, Kamigohri, Ako-gun, Hyogo, 678-1297, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Fukunaga
authors.affiliation: Department of Life Science, Graduate School of Life Science, University of Hyogo, 3-2-1 Kohto, Kamigohri, Ako-gun, Hyogo, 678-1297, Japan.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Nishino
authors.affiliation: Department of Life Science, Graduate School of Life Science, University of Hyogo, 3-2-1 Kohto, Kamigohri, Ako-gun, Hyogo, 678-1297, Japan.
authors.forename: Atsuo
authors.initials: A
authors.lastname: Miyazawa
authors.affiliation: Department of Life Science, Graduate School of Life Science, University of Hyogo, 3-2-1 Kohto, Kamigohri, Ako-gun, Hyogo, 678-1297, Japan. kashino@sci.u-hyogo.ac.jp.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kashino
authors.affiliation: Department of Life Science, Graduate School of Life Science, University of Hyogo, 3-2-1 Kohto, Kamigohri, Ako-gun, Hyogo, 678-1297, Japan.
authors.forename: Natsuko
authors.initials: N
authors.lastname: Inoue-Kashino
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D017377:Diatoms / Q000378:metabolism* / Q000528:radiation effects; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D020524:Thylakoids / Q000378:metabolism; D024341:Xanthophylls / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D024341:Xanthophylls; C088752:fucoxanthin-, chlorophyll a-c-containing protein; C025164:fucoxanthin; D002734:Chlorophyll; C033808:diadinoxanthin; C064041:chlorophyll c; C103105:diatoxanthin; D000077194:Chlorophyll A
keywords: 2D-PAGE; Chaetoceros gracilis; Diatom; FCP; IEF; Isoelectric focusing