Two types of fucoxanthin-chlorophyll-binding proteins I tightly bound to the photosystem I core complex in marine centric diatoms

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Abstract

Intact fucoxanthin (Fucox)-chlorophyll (Chl)-binding protein I-photosystem I supercomplexes (FCPI-PSIs) were prepared by a newly developed simple fast procedure from centric diatoms Chaetoceros gracilis and Thalassiosira pseudonana to study the mechanism of their efficient solar energy accumulation. FCPI-PSI purified from C. gracilis contained 252 Chl a, 23 Chl c, 56 Fucox, 34 diadinoxanthin + diatoxanthin, 1 violaxanthin, 21 ß-carotene, and 2 menaquinone-4 per P700. The complex showed a high electron transfer activity at 185,000 μmol mg Chl a 1 · h 1 to reduce methyl viologen from added cytochrome c6. We identified 14 and 21 FCP proteins in FCPI-PSI of C. gracilis and T. pseudonana, respectively, determined by N-terminal and internal amino acid sequences and liquid chromatography–tandem mass spectrometry (LC–MS/MS) analyses. PsaO and a red lineage Chla/b-binding-like protein (RedCAP), Thaps3:270215, were also identified. Severe detergent treatment of FCPI-PSI released FCPI-1 first, leaving the FCPI-2-PSI-core complex. FCPI-1 contained more Chl c and showed Chl a fluorescence at a shorter wavelength than FCPI-2, suggesting an excitation-energy transfer from FCPI-1 to FCPI-2 and then to the PSI core. Fluorescence emission spectra at 17 K in FCPI-2 varied depending on the excitation wavelength, suggesting two independent energy transfer routes. We formulated a model of FCPI-PSI based on the biochemical assay results.

Highlights

► A simple fast procedure from two centric diatoms was developed. ► PSI complexes have a high transport activity. ► A red lineage Chla/b-binding-like protein (RedCAP) was found. ► Two types of fucoxanthin-chlorophyll-binding proteins I in diatom PSI is proposed.

Abbreviations

Chl
chlorophyll
PSI and PSII
photosystems I and II
LHC
light-harvesting chlorophyll-binding protein
FCPI
fucoxanthin-chlorophyll-binding protein I
LIL protein
light-harvesting-like protein
RedCAP
red lineage Chla/b-binding-like protein
P700
primary electron donor chlorophyll dimer of Photosystem I
DDM
n-dodecyl-ß-d-maltoside
SDS–PAGE
sodium dodecyl sulfate–polyacrylamide gel electrophoresis
BN-PAGE
blue native polyacrylamide gel electrophoresis
SDG
sucrose density gradient
LC–MS/MS
liquid chromatography–tandem mass spectrometry
HPLC
high-performance liquid chromatography
Fucox
fucoxanthin
Ddx
diadinoxanthin
Dtx
diatoxanthin
Vx
violaxanthin
MK-4
menaquinone-4

Keywords

Photosystem I
Fucoxanthin-chlorophyll-binding protein I
Diatom
Chaetoceros gracilis
Thalassiosira pseudonana

Cited by (0)

1

Current address: Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan.

2

Current address: Center for Gene Research, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8601, Japan.

3

Current address: Department of Life Science, Faculty of Science and Engineering, University of Chuo, 1-13-27 Kasuga, Bunkyo, Tokyo 112-8551, Japan.