Masayuki Komura

University of Hyogo, Kōbe-shi, Hyogo-ken, Japan

Are you Masayuki Komura?

Claim your profile

Publications (11)33.22 Total impact

  • Source
    [Show abstract] [Hide abstract]
    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.
  • Source
    [Show abstract] [Hide abstract]
    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 showedChl a fluorescence at a shorter wavelength than FCPI-2, suggesting an excitation-energy transfer fromFCPI-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 amodel of FCPI-PSI based on the biochemical assay results.
  • Source
    [Show abstract] [Hide abstract]
    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 185,000μmolmg 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 17K 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.
    Biochimica et Biophysica Acta 02/2013; 1827:529-539. · 4.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A time-resolved fluorescence study of living lichen thalli at 5 K was conducted to clarify the dynamics and mechanism of the effective dissipation of excess light energy taking place in lichen under extreme drought conditions. The decay-associated spectra obtained from the experiment at 5 K were characterized by a drastically sharpened spectral band which could not be resolved by experiments at higher temperatures. The present results indicated the existence of two distinct dissipation components of excess light energy in desiccated lichen; one is characterized as rapid fluorescence decay with a time constant of 27 ps in the far-red region that was absent in wet lichen thalli, and the other is recognized as accelerated fluorescence decay in the 685-700 nm spectral region. The former energy-dissipation component with extremely high quenching efficiency is most probably ascribed to the emergence of a rapid quenching state in the peripheral-antenna system of photosystem II (PS II) on desiccation. This is an extremely effective protection mechanism of PS II under desiccation, which lichens have developed to survive in the severely desiccated environments. The latter, which is less efficient at 5 K, might have a supplementary role and take place either in the core antenna of PS II or aggregated peripheral antenna of PS II.
    Photosynthesis Research 10/2011; 110(1):39-48. · 3.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The ultrafast fluorescence dynamics of photosystem I (PS I) purified from a marine centric diatom, Chaetoceros gracilis, at 17 K was studied using fluorescence up-conversion and streak-camera setups. The experiments were done for two kinds of sample preparations containing different amounts of the peripheral antenna proteins, the fucoxanthin-chlorophyll (Chl) binding proteins associated with PS I (FCPI). Upon excitation at 430 nm, which selectively excites Chl a mainly contained in the core complex, the fluorescence dynamics of both samples was roughly expressed by four decay-associated spectra (DASs) with time constants of ca. 5, ca. 22, ca. 100, and ca. 400 ps. These DAS components have corresponding counterparts in the results of a previous study of Thermosynechococcus elongatus PS I (Shibata et al. J. Phys. Chem. B 2010, 114, 2954) except for that with a time constant of ca. 22 ps. The similar distribution of the time constants suggests a shared light-harvesting pathway by PS I of these two organisms. The DAS with a ca. 400 ps time constant has its peak wavelength at around 710 nm, suggesting the presence of antenna pigment states with slightly lower excitation energy than that of P700. This antenna state acts as a shallow sink in the core complex of the diatom PS I and causes a specific temperature dependence of its fluorescence spectrum below 77 K. Excitation energy funneling into the shallow-sink state seems to take place within 0.2 ps, suggesting an extremely efficient energy transfer. Upon the selective excitation of Chl c in FCPI by a 460 nm laser, three DAS components suggesting excitation energy transfers were obtained. The 0.2 ps DAS shows the energy transfer from Chl c to Chl a within FCPI, while the 0.7 and 40 ps DASs suggest the energy transfer from FCPI to the core complex. The excitation energy seems to be effectively transferred from FCPI to the core complex in diatom PS I because the selective excitation of Chl c in FCPI does not induce a severe retardation of the overall light-harvesting kinetics.
    The Journal of Physical Chemistry B 07/2010; 114(27):9031-8. · 3.61 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The mechanism of the severe quenching of chlorophyll (Chl) fluorescence under drought stress was studied in a lichen Physciella melanchla, which contains a photobiont green alga, Trebouxia sp., using a streak camera and a reflection-mode fluorescence up-conversion system. We detected a large 0.31 ps rise of fluorescence at 715 and 740 nm in the dry lichen suggesting the rapid energy influx to the 715-740 nm bands from the shorter-wavelength Chls with a small contribution from the internal conversion from Soret bands. The fluorescence, then, decayed with time constants of 23 and 112 ps, suggesting the rapid dissipation into heat through the quencher. The result confirms the accelerated 40 ps decay of fluorescence reported in another lichen (Veerman et al., 2007 [36]) and gives a direct evidence for the rapid energy transfer from bulk Chls to the longer-wavelength quencher. We simulated the entire PS II fluorescence kinetics by a global analysis and estimated the 20.2 ns(-1) or 55.0 ns(-1) energy transfer rate to the quencher that is connected either to the LHC II or to the PS II core antenna. The strong quenching with the 3-12 times higher rate compared to the reported NPQ rate, suggests the operation of a new type of quenching, such as the extreme case of Chl-aggregation in LHCII or a new type of quenching in PS II core antenna in dry lichens.
    Biochimica et Biophysica Acta 12/2009; 1797(3):331-8. · 4.66 Impact Factor
  • Source
    Masayuki Komura, Shigeru Itoh
    [Show abstract] [Hide abstract]
    ABSTRACT: We describe here a recently developed fluorescence measurement system that uses a streak camera to detect fluorescence decay in a single photon-counting mode. This system allows for easy measurements of various samples and provides 2D images of fluorescence in the wavelength and time domains. The great advantage of the system is that the data can be handled with ease; furthermore, the data are amenable to detailed analysis. We describe the picosecond kinetics of fluorescence in spinach Photosystem (PS) II particles at 4-77 K as a typical experimental example. Through the global analysis of the data, we have identified a new fluorescence band (F689) in addition to the already established F680, F685, and F695 emission bands. The blue shift of the steady-state fluorescence spectrum upon cooling below 77 K can be interpreted as an increase of the shorter-wavelength fluorescence, especially F689, due to the slowdown of the excitation energy transfer process. The F685 and F695 bands seem to be thermally equilibrated at 77 K but not at 4 K. The simple and efficient photon accumulation feature of the system allows us to measure fluorescence from leaves, solutions, single colonies, and even single cells. The 2D fluorescence images obtained by this system are presented for isolated spinach PS II particles, intact leaves of Arabidopsis thaliana, the PS I super-complex of a marine centric diatom, Chaetoceros gracilis, isolated membranes of a purple photosynthetic bacterium, Acidiphilium rubrum, which contains Zn-BChl a, and a coral that contains a green fluorescent protein and an algal endosymbiont, Zooxanthella.
    Photosynthesis Research 08/2009; 101(2-3):119-33. · 3.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To analyze the role of phosphatidylglycerol (PG) in photosynthetic membranes of cyanobacteria we used two mutants of Synechocystis sp. PCC6803: the PAL mutant which has no phycobilisomes and shows a high PSII/ PSI ratio, and a mutant derived from it by inactivating its cdsA gene encoding cytidine 5'-diphosphate diacylglycerol synthase, a key enzyme in PG synthesis. In a medium supplemented with PG the PAL/ΔcdsA mutant cells grew photoautotrophically. Depletion of PG in the medium resulted (a) in an arrest of cell growth and division, (b) in a slowdown of electron transfer from the acceptor QA to QB in PSII and (c) in a modification of chlorophyll fluorescence curve. The depletion of PG affected neither the redox levels of QA nor the S2 state of the oxygen-evolving manganese complex, as indicated by thermoluminescence studies. Two-dimensional PAGE showed that in the absence of PG (a) the PSII dimer was decomposed into monomers, and (b) the CP43 protein was detached from a major part of the PSII core complex. [35S]-methionine labeling confirmed that PG depletion did not block de novo synthesis of the PSII proteins. We conclude that PG is required for the binding of CP43 within the PSII core complex
    Biochimica et Biophysica Acta 06/2008; · 4.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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 (approximately 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 A1 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.
    Biochimica et Biophysica Acta 05/2008; 1777(4):351-61. · 4.66 Impact Factor
  • Masayuki Komura, Ikuko Iwasaki, Shigeru Itoh
    [Show abstract] [Hide abstract]
    ABSTRACT: Lichens survive under the extreme drought environments. It has been suggested that dried lichens convert excess light energy into heat by unknown mechanism to prevent the accumulation of harmful photoproducts. We studied 18 lichen species by their steady-state fluorescence spectra, PAM and picosecond time-resolved fluorescence decay profiles at 4–300 K. Quantitative analyses of the decay profiles were applied. We obtained the following results: (1) All dried lichens showed a low intensity of PS II fluorescence; (2) the picosecond decays of PS II fluorescence were fast (<10 ps) in most dry lichens; (3) the excitation energy transfer from LHC II to CP43/CP47 was still active; (4) the lifetime of the PS I fluorescence was little affected; (5) the changes were fully reversed within 1 min after the re-hydration; and (6) some lichens showed no fast decay of PS II fluorescence. We noticed two different types of drought-induced energy dissipation mechanisms: Most of lichens dissipated almost all the excitation energy in a few picoseconds by an unknown quencher; some lichens decreased the antenna size of PS II by the state transition mechanism. The new type of the quencher found in this study seems to be situated in the core antenna, and is different from the well-known non-photochemical quenching mechanism.
    12/2007: pages 1023-1026;
  • Source
    Masayuki Komura, Yutaka Shibata, Shigeru Itoh
    [Show abstract] [Hide abstract]
    ABSTRACT: We performed picosecond time-resolved fluorescence spectroscopy in spinach photosystem II (PS II) particles at 4, 40, and 77 K and identified a new fluorescence band, F689. F689 was identified in addition to the well-known F685 and F695 bands in both analyses of decay-associated spectra and global Gaussian deconvolution of time-resolved spectra. Its fast decay suggests the energy transfer directly from F689 to the reaction center chlorophyll P680. The contribution of F689, which increases only at low temperature, explains the unusually broad and variable bandwidth of F695 at low temperature. Global analysis revealed the three types of excitation energy transfer/dissipation processes: (1) energy transfer from the peripheral antenna to the three core antenna bands F685, F689, and F695 with time constants of 29 and 171 ps at 77 and 4 K, respectively; (2) between the three core bands (0.18 and 0.82 ns); and (3) the decays of F689 (0.69 and 3.02 ns) and F695 (2.18 and 4.37 ns). The retardations of these energy transfer rates and the slow F689 decay rate produced the strong blue shift of the PS II fluorescence upon the cooling below 77 K.
    Biochimica et Biophysica Acta 01/2007; 1757(12):1657-68. · 4.66 Impact Factor