Characterization of highly purified photosystem I complexes from the chlorophyll d-dominated cyanobacterium Acaryochloris marina MBIC 11017.
Photochemically active photosystem (PS) I complexes were purified from the chlorophyll (Chl) d-dominated cyanobacterium Acaryochloris marina MBIC 11017, and several of their properties were characterized. PS I complexes consist of 11 subunits, including PsaK1 and PsaK2; a new small subunit was identified and named Psa27. The new subunit might replace the function of PsaI that is absent in A. marina. The amounts of pigments per one molecule of Chl d' were 97.0 +/- 11.0 Chl d, 1.9 +/- 0.5 Chl a, 25.2 +/- 2.4 alpha-carotene, and two phylloquinone molecules. The light-induced Fourier transform infrared difference spectroscopy and light-induced difference absorption spectra reconfirmed that the primary electron donor of PS I (P740) was the Chl d dimer. In addition to P740, the difference spectrum contained an additional band at 728 nm. The redox potentials of P740 were estimated to be 439 mV by spectroelectrochemistry; this value was comparable with the potential of P700 in other cyanobacteria and higher plants. This suggests that the overall energetics of the PS I reaction were adjusted to the electron acceptor side to utilize the lower light energy gained by P740. The distribution of charge in P740 was estimated by a density functional theory calculation, and a partial localization of charge was predicted to P1 Chl (special pair Chl on PsaA). Based on differences in the protein matrix and optical properties of P740, construction of the PS I core in A. marina was discussed.
Tomo
Tatsuya
T
Department of Technology and Ecology, Hall of Global Environmental Research, Kyoto University, Kyoto, Japan. tomo@z05.mbox.media.kyoto-u.ac.jp
Kato
Yuki
Y
Suzuki
Takehiro
T
Akimoto
Seiji
S
Okubo
Tatsunori
T
Noguchi
Takumi
T
Hasegawa
Koji
K
Tsuchiya
Tohru
T
Tanaka
Kazunori
K
Fukuya
Michitaka
M
Dohmae
Naoshi
N
Watanabe
Tadashi
T
Mimuro
Mamoru
M
D000595:Amino Acid Sequence; D002734:Chlorophyll / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism*; D019281:Dimerization; D004583:Electrons; D008027:Light; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D013053:Spectrophotometry / Q000379:methods; D017550:Spectroscopy, Fourier Transform Infrared
D045331:Photosystem I Protein Complex; D002734:Chlorophyll; C107509:chlorophyll d