Photosystem I complexes associated with fucoxanthin-chlorophyll-binding proteins from a marine centric diatom, Chaetoceros gracilis

• Published in: Biochimica et biophysica acta 2008-04, Vol.1777 (4), p.351-361
• Main Authors: Ikeda, Yohei, Komura, Masayuki, Watanabe, Mai, Minami, Chie, Koike, Hiroyuki, Itoh, Shigeru, Kashino, Yasuhiro, Satoh, Kazuhiko
• Format: Article
• Language: English
• Subjects: Cell Fractionation; Chaetoceros gracilis; Diatom; Diatoms - chemistry; Energy Transfer; Fucoxanthin-chlorophyll-binding protein; Light-Harvesting Protein Complexes - metabolism; Photosystem I; Photosystem I Protein Complex - metabolism; Spectrometry, Fluorescence; Spectrophotometry; Thylakoids - chemistry; Time-resolved fluorescence spectra
• ISSN: 0005-2728; 0006-3002; 1879-2650
• DOI: 10.1016/j.bbabio.2008.01.011

Diatoms occupy a key position as a primary producer in the global aquatic ecosystem. We developed methods to isolate highly intact thylakoid membranes and the photosystem I (PS I) complex from a marine centric diatom, Chaetoceros gracilis. The PS I reaction center (RC) was purified as a super complex with light-harvesting fucoxanthin-chlorophyll (Chl)-binding proteins (FCP). The super complex contained 224 Chl a, 22 Chl c, and 55 fucoxanthin molecules per RC. The apparent molecular mass of the purified FCP–PS I super complex (∼ 1000 kDa) indicated that the super complex was composed of a monomer of the PS I RC complex and about 25 copies of FCP. The complex contained menaquinone-4 as the secondary electron acceptor A 1 instead of phylloquinone. Time-resolved fluorescence emission spectra at 77 K indicated that fast (16 ps) energy transfer from a Chl a band at 685 nm on FCP to Chls on the PS I RC complex occurs. The ratio of fucoxanthin to Chl a on the PS I-bound FCP was lower than that of weakly bound FCP, suggesting that PS I-bound FCP specifically functions as the mediator of energy transfer between weakly bound FCPs and the PS I RC.