Publications by authors named "Hiroyuki Mino"

60 Publications

The evolutionary conserved iron-sulfur protein TCR controls P700 oxidation in photosystem I.

iScience 2021 Feb 13;24(2):102059. Epub 2021 Jan 13.

Department of Life Science and Technology, Tokyo Institute of Technology, Yokohama 226-8501, Japan.

In natural habitats, plants have developed sophisticated regulatory mechanisms to optimize the photosynthetic electron transfer rate at the maximum efficiency and cope with the changing environments. Maintaining proper P700 oxidation at photosystem I (PSI) is the common denominator for most regulatory processes of photosynthetic electron transfers. However, the molecular complexes and cofactors involved in these processes and their function(s) have not been fully clarified. Here, we identified a redox-active chloroplast protein, the triplet-cysteine repeat protein (TCR). TCR shared similar expression profiles with known photosynthetic regulators and contained two triplet-cysteine motifs (CxxxCxxxC). Biochemical analysis indicated that TCR localizes in chloroplasts and has a [3Fe-4S] cluster. Loss of TCR limited the electron sink downstream of PSI during dark-to-light transition. double mutant reduced growth significantly and showed unusual oxidation and reduction of plastoquinone pool. These results indicated that TCR is involved in electron flow(s) downstream of PSI, contributing to P700 oxidation.
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http://dx.doi.org/10.1016/j.isci.2021.102059DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7848650PMC
February 2021

Formation of the High-Spin S State Related to the Extrinsic Proteins in the Oxygen Evolving Complex of Photosystem II.

J Phys Chem Lett 2020 Oct 6;11(20):8908-8913. Epub 2020 Oct 6.

Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, 464-8602 Nagoya, Aichi, Japan.

The high-spin S state was investigated with photosystem II (PSII) from spinach, , and . In extrinsic protein-depleted PSII, high-spin electron paramagnetic resonance (EPR) signals were not detected in either species, whereas all species showed ∼ 5 signals in the presence of a high concentration of Ca instead of the multiline signal. In the intact and PsbP/Q-depleted PSII from spinach, the = 4.1 EPR signal was detected. These results show that formation of the high-spin S state of the manganese cluster is regulated by the extrinsic proteins through a charge located near the Mn4 atom in the MnCaO cluster but is independent of the intrinsic proteins. The shift to the ∼ 5 state is caused by tilting of the -axis in the Mn4 coordinates through hydrogen bonds or external divalent cations. The structural modification may allow insertion of an oxygen atom during the S-to-S transition.
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http://dx.doi.org/10.1021/acs.jpclett.0c02411DOI Listing
October 2020

Molecular Structure of the S State with a = 5 Signal in the Oxygen Evolving Complex of Photosystem II.

J Phys Chem B 2020 07 25;124(27):5531-5537. Epub 2020 Jun 25.

Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, 464-8602 Nagoya, Aichi, Japan.

The -factor shift of the = 4.1 EPR signal was detected in spinach PsbO/P/Q-depleted PS II. The effective -factor of the signal shifts up to ∼4.9, depending on the Ca concentration. Hyperfine structure spacing with about 3 mT was detected in this = 5 (4.9) signal. The shift to = 5 (4.9) was related to the distortion of the manganese cluster, derived from the modification of the chemical bond or the crystalline field of the Mn4(III) in the manganese cluster. Based on the EPR analysis of the = 5 (4.9) spin state, another molecular structure of the S state, a "distant Mn" structure, was discussed as an intermediate state between the S and S states.
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http://dx.doi.org/10.1021/acs.jpcb.0c02913DOI Listing
July 2020

Orientation of Ligand Field for Dangling Manganese in Photosynthetic Oxygen-Evolving Complex of Photosystem II.

J Phys Chem B 2020 01 23;124(1):128-133. Epub 2019 Dec 23.

Division of Material Science, Graduate School of Science , Nagoya University , Furo-cho , Chikusa-ku, 464-8602 Nagoya , Aichi , Japan.

The spin structure in the S state and the crystal structure of the manganese cluster of the oxygen-evolving complex of plant photosystem II were combined by the quantitative evaluation of the magnetic anisotropy of the = 4 signal. The -values of 3.93 and 4.13 were obtained for the = 4 signal in the directions parallel and perpendicular to the membrane normal, respectively. The peak-to-peak separations were 270 and 420 G for the parallel and perpendicular orientations to the membrane, respectively. By comparison with the crystal structure, the -axis of the zero-field splitting was ascribed to the direction of the dangling Mn connecting water oxygen, Mn4-O(W1), in the manganese cluster. The results give the first experimental evidence that the valence of the dangling Mn is Mn(III) in the S high-spin state. We showed that the strong exchange coupling of Mn4 to Mn3 was required for = 4.1 spin state in the four-spin couplings, estimated as > ∼|-30 cm|, indicating that the present closed cubane model in quantum mechanics/molecular mechanics (QM/MM) calculation cannot explain the = 4.1 spin structure. The onsite zero-field splitting of the dangling Mn was evaluated as -2.3 cm under the strong antiferromagnetic couplings (-50 cm) with the dangling Mn to the cubane frame in the four coupled spin state. From the viewpoint of the arrangement of the Mn valences in the cluster, a closed cubane model is effective, but without a large structural deviation from the S state crystal structure.
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http://dx.doi.org/10.1021/acs.jpcb.9b10817DOI Listing
January 2020

Modeling of spike trains in auditory nerves with self-exciting point processes of the von Mises type.

Authors:
Hiroyuki Mino

Biol Cybern 2019 06 19;113(3):347-356. Epub 2019 Apr 19.

Department of Electrical Engineering, Kanto Gakuin University, 1-50-1 Mutsuura E., Kanazawa-ku, Yokohama, 236-8501, Japan.

This article presents the modeling of spike trains in auditory nerve fiber (ANF) models with a one-memory self-exciting point process (SEPP) of the von Mises type. The ANF models were acoustically stimulated by a synaptic current of inner hair cells, or electrically stimulated by sinusoidally amplitude-modulated pulsatile waveforms. It has been shown that the parameters of one-memory SEPP of the von Mises type could be estimated by numerically maximizing the likelihood function from sample realizations of the spike trains in response to acoustic or electric stimulus. Furthermore, it was found that period histograms of the one-memory SEPP generated artificially on the basis of the estimated von Mises parameters agreed well with those of acoustic or electric stimulus, by performing the uniform-scores test. It implies that the waveforms of pulsatile electric stimuli should be selected such that the spike trains can be represented by one-memory SEPP of the von Mises type with appropriate parameters, efficiently carrying information to the cochlear implant user's brain, like that in acoustic stimulation of the healthy ear. The findings presented in this paper may play an important role in determining optimal parameters of pulsatile electric stimuli by using one-memory SEPP of the von Mises type, and further in the design of better cochlear prostheses.
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http://dx.doi.org/10.1007/s00422-019-00799-5DOI Listing
June 2019

Flavin-Radical Formation in the Light-Oxygen-Voltage-Sensing Domain of the Photozipper Blue-light Sensor Protein.

J Phys Chem B 2018 09 11;122(38):8819-8823. Epub 2018 Sep 11.

Division of Material Science, Graduate School of Science , Nagoya University , Chikusa-ku, Furo-cho, Nagoya 464-8602 , Japan.

Formation of the neutral flavin radical in the light-oxygen-voltage-sensing (LOV-sensing) domain of photozipper, based on VfAUREO1, was investigated by electron paramagnetic resonance spectroscopy. The flavin radical was observed in the presence of dithiothreitol by illumination of a LOV-domain mutant (C254S), in which a photoactive cysteine residue in close proximity to flavin was replaced with a serine. The radical did not form under low initial protein-concentration conditions (less than 20 μM). The flavin radicals accumulated with logistic time-dependent kinetics when the protein concentrations were higher than 30 μM. These results indicate that the radical is produced by concerted reactions involving protein interactions and that the radical is formed from the LOV dimer but not the LOV monomer. In contrast, logistic time dependencies were not observed for the sample adapted to the dark following radical formation by illumination, indicating that initialization of the proton pathway is essential for this fast sensing reaction.
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http://dx.doi.org/10.1021/acs.jpcb.8b05808DOI Listing
September 2018

Magnetic structure of manganese cluster in photosystem II investigated by electron paramagnetic resonance.

Biophys Physicobiol 2018 6;15:45-50. Epub 2018 Feb 6.

Division of Material Science (Physics), Graduate School of Science, Nagoya University, Nagoya, Aichi 464-8602, Japan.

The electronic structure of manganese (Mn) cluster in photosystem II was investigated by electron paramagnetic resonance (EPR) spectroscopy. In order to determine the spin density distribution in magnetically coupled Mn in the S state Mn cluster, pulsed electron-electron double resonance (PELDOR) measurement was performed. The local environment of the Mn cluster was investigated by electron-nuclear double resonance (ENDOR). Using spin projections determined by PELDOR, ENDOR signals were assigned to the water molecules ligated to the Mn cluster. The location of a high-affinity Mn site in apo-photosystem II, which is the initial site of photoactivation of the Mn cluster, was determined by PELDOR.
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http://dx.doi.org/10.2142/biophysico.15.0_45DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5873039PMC
February 2018

Location of the extrinsic subunit PsbP in photosystem II studied by pulsed electron-electron double resonance.

Biochim Biophys Acta Bioenerg 2018 May 8;1859(5):394-399. Epub 2018 Mar 8.

Division of Material Science (Physics), Graduate school of Science, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8602, Japan. Electronic address:

The binding site of the extrinsic protein PsbP in plant photosystem II was mapped by pulsed electron-electron double resonance, using mutant spinach PsbP (Pro20Cys, Ser82Cys, Ala111Cys, and Ala186Cys) labeled with 4-maleimido-TEMPO (MSL) spin label. The distances between the spin label and the Tyr160 neutral radical (Y) in PsbD, the D2 subunit of plant photosystem II, were 50.8 ± 3.5 Å, 54.9 ± 4.0 Å, 57.8 ± 4.9 Å, and 58.4 ± 14.1 Å, respectively. The geometry inferred from these distances was fitted to the PsbP crystal structure (PDB: 4RTI) to obtain the coordinates of Y relative to PsbP. These coordinates were then fitted under boundary conditions to the structure of cyanobacterial photosystem II (PDB: 4UB6), by rotating on Euler angles centered at fixed Y coordinates. The result proposed two models which show possible acidic amino acid residues in CP43, CP47 and D2 that can bind the basic amino acids Arg48, Lys143, and Lys160 in PsbP.
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http://dx.doi.org/10.1016/j.bbabio.2018.03.002DOI Listing
May 2018

Dimeric Structure of the Blue Light Sensor Protein Photozipper in the Active State.

Biochemistry 2018 02 21;57(5):494-497. Epub 2017 Dec 21.

Division of Material Science, Graduate School of Science, Nagoya University , Chikusa-ku, Furo-cho, Nagoya 464-8602, Japan.

The light oxygen voltage-sensing (LOV) domain plays a crucial role in blue light (BL) sensing in plants and microorganisms. LOV domains are usually associated with the effector domains and regulate the activities of effector domains in a BL-dependent manner. Photozipper (PZ) is monomeric in the dark state. BL induces reversible dimerization of PZ and subsequently increases its affinity for the target DNA sequence. In this study, we report the analyses of PZ by pulsed electron-electron double resonance (PELDOR). The neutral flavin radical was formed by BL illumination in the presence of dithiothreitol in the LOV-C254S (without the bZIP domain) and PZ-C254S mutants, where the cysteine residue responsible for adduct formation was replaced with serine. The magnetic dipole interactions of 3 MHz between the neutral radicals were detected in both LOV-C254S and PZ-C254S, indicating that these mutants are dimeric in the radical state. The PELDOR simulation showed that the distance between the radical pair is close to that estimated from the dimeric crystal structure in the "light state" [Heintz, U., and Schlichting, I. (2016) eLife 5, e11860], suggesting that in the radical state, LOV domains in PZ-C254S form a dimer similar to that of LOV-C254S, which lacks the bZIP domain.
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http://dx.doi.org/10.1021/acs.biochem.7b01045DOI Listing
February 2018

On a unified point process approach for the characterization of bioelectric discrete phenomena.

Annu Int Conf IEEE Eng Med Biol Soc 2017 Jul;2017:4018-4021

This paper discusses a unified method based on the theory of point processes to characterize various types of bioelectric discrete signals such as heart beat timing, myoelectric activity, discharge of primary sensory neurons or neurons in the central nervous systems. The doubly stochastic point processes, in which the discrete event occurring intensity is stochastic, forms the most general class to characterize the discrete phenomena. In this paper the self-exciting process has been shown to be useful to characterize wide range of discrete biosignals. The modeling of conditional intensity function is the essential part of the characterization. When the intensity has a parametric model, the maximum likelihood parameter estimation will be the useful way to characterize the phenomena. The effectiveness of the method is demonstrated by a specific modeling of the spontaneous neuronal burst discharges recorded from the brain thalamus during the neuro surgery. The first approximation model has four parameters obtained by the instantaneous nonlinearly transformed sinusoidal function. An extended model allows arbitrary periodic intensity with refractory period. Predicted interval histograms show good agreement with the observed ones indicating the validity of the proposed method.
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http://dx.doi.org/10.1109/EMBC.2017.8037737DOI Listing
July 2017

Mechanism of Photodamage of the Oxygen Evolving Mn Cluster of Photosystem II by Excessive Light Energy.

Sci Rep 2017 08 8;7(1):7604. Epub 2017 Aug 8.

Division of Material Science (Physics), Graduate school of Science, Nagoya University, Furo-cho, Chikusa, Nagoya, 464-8602, Japan.

Photodamage to Photosystem II (PSII) has been attributed either to excessive excitation of photosynthetic pigments or by direct of light absorption by MnCaO cluster. Here we investigated the time course of PSII photodamage and release of Mn in PSII-enriched membranes under high light illumination at 460 nm and 660 nm. We found that the loss of PSII activity, assayed by chlorophyll fluorescence, is faster than release of Mn from the MnCaO cluster, assayed by EPR. Loss of PSII activity and Mn release was slower during illumination in the presence of exogenous electron acceptors. Recovery of PSII activity was observed, after 30 min of addition of electron donor post illumination. The same behavior was observed under 460 and 660 nm illumination, suggesting stronger correlation between excessive excitation and photodamage compared to direct light absorption by the cluster. A unified model of PSII photodamage that takes into account present and previous literature reports is presented.
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http://dx.doi.org/10.1038/s41598-017-07671-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5548768PMC
August 2017

Hyperfine Sublevel Correlation Spectroscopy Studies of Iron-Sulfur Cluster in Rieske Protein from Green Sulfur Bacterium Chlorobaculum tepidum.

J Phys Chem B 2017 03 17;121(12):2543-2553. Epub 2017 Mar 17.

Division of Material Science, Graduate School of Science, Nagoya University , Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan.

The magnetic properties of the Rieske protein purified from Chlorobaculum tepidum were investigated using electron paramagnetic resonance and hyperfine sublevel correlation spectroscopy (HYSCORE). The g-values of the FeS center were g = 1.81, g = 1.90, and g = 2.03. Four classes of nitrogen signals were obtained by HYSCORE. Nitrogens 1 and 2 had relatively strong magnetic hyperfine couplings and were assigned as the nitrogen directly ligated to Fe. Nitrogens 3 and 4 had relatively weak magnetic hyperfine couplings and were assigned as the other nitrogen of the His ligands and peptide nitrogen connected to the sulfur atom via hydrogen bonding, respectively. The anisotropy of nitrogen 3 reflects the different spin density distributions on the His ligands, which influences the electron transfer to quinone.
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http://dx.doi.org/10.1021/acs.jpcb.6b12968DOI Listing
March 2017

Regulated Electron Tunneling of Photoinduced Primary Charge-Separated State in the Photosystem II Reaction Center.

J Phys Chem Lett 2017 Mar 27;8(6):1179-1184. Epub 2017 Feb 27.

Department of Chemistry, Graduate School of Science, Kobe University , 1-1 Rokkodaicho, Nada-ku, Kobe 657-8501, Japan.

In initial events of the photosynthesis by higher plants, the photosystem II (PSII) generates photoinduced primary charge-separated (CS) state composed of reduced pheophytin (Pheo) and oxidized special pair (P) in chlorophyll a (Chla) P/P in the D1/D2 heterodimer, ultimately leading to the water oxidation at the oxygen-evolving MnCaO cluster by P. To understand the mechanism of the efficient generation of initially localized CS state (P Pheo), we have characterized cofactor geometries and electronic coupling of the photoinduced primary CS state in quinone prereduced membrane of PSII from spinach using the time-resolved electron paramagnetic resonance method. It has been revealed that the electronic coupling between the charges is significantly weak in the CS state separated by 1.5 nm, showing the importance of regulated cofactor-cofactor electronic interaction between a vinyl substituent in Pheo and an accessory chlorophyll to inhibit the energy-wasting charge recombination after the primary electron-transfer processes.
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http://dx.doi.org/10.1021/acs.jpclett.7b00044DOI Listing
March 2017

Location of Methanol on the S State Mn Cluster in Photosystem II Studied by Proton Matrix Electron Nuclear Double Resonance.

J Phys Chem Lett 2017 Feb 20;8(3):621-625. Epub 2017 Jan 20.

Division of Material Science, Graduate School of Science, Nagoya University , Furo-cho, Chikusa-ku, 464-8602 Nagoya, Aichi, Japan.

Proton matrix electron nuclear double resonance (ENDOR) spectroscopy was performed to specify the location of the methanol molecule near the manganese cluster in photosystem II. Comparison of the ENDOR spectra in the presence of CHOH and CDOH revealed two pairs of hyperfine couplings, 1.2 MHz for A and 2.5 MHz for A, arising from the methyl group in methanol. On the basis of the crystal structure, the possible location of methanol close to the manganese cluster was discussed.
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http://dx.doi.org/10.1021/acs.jpclett.7b00110DOI Listing
February 2017

Proton Matrix ENDOR Studies on Ca2+-depleted and Sr2+-substituted Manganese Cluster in Photosystem II.

J Biol Chem 2015 Nov 5;290(47):28166-28174. Epub 2015 Oct 5.

Graduate School of Science, Nagoya University, Furo-cho, Chikusa, Nagoya, 464-8602, Japan. Electronic address:

Proton matrix ENDOR spectra were measured for Ca(2+)-depleted and Sr(2+)-substituted photosystem II (PSII) membrane samples from spinach and core complexes from Thermosynechococcus vulcanus in the S2 state. The ENDOR spectra obtained were similar for untreated PSII from T. vulcanus and spinach, as well as for Ca(2+)-containing and Sr(2+)-substituted PSII, indicating that the proton arrangements around the manganese cluster in cyanobacterial and higher plant PSII and Ca(2+)-containing and Sr(2+)-substituted PSII are similar in the S2 state, in agreement with the similarity of the crystal structure of both Ca(2+)-containing and Sr(2+)-substituted PSII in the S1 state. Nevertheless, slightly different hyperfine separations were found between Ca(2+)-containing and Sr(2+)-substituted PSII because of modifications of the water protons ligating to the Sr(2+) ion. Importantly, Ca(2+) depletion caused the loss of ENDOR signals with a 1.36-MHz separation because of the loss of the water proton W4 connecting Ca(2+) and YZ directly. With respect to the crystal structure and the functions of Ca(2+) in oxygen evolution, it was concluded that the roles of Ca(2+) and Sr(2+) involve the maintenance of the hydrogen bond network near the Ca(2+) site and electron transfer pathway to the manganese cluster.
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http://dx.doi.org/10.1074/jbc.M115.675496DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4653675PMC
November 2015

Location of the High-Affinity Mn(2+) Site in Photosystem II Detected by PELDOR.

J Phys Chem B 2015 Aug 4;119(32):10139-44. Epub 2015 Aug 4.

Division of Material Science (Physics), Graduate School of Science, Nagoya University, Furo-cho, Chikusa, Nagoya, 464-8602, Japan.

The location of the high-affinity Mn(2+) site in apo-photosystem (PS) II was investigated by pulsed EPR. The electron-electron magnetic dipole interaction of 1.7 MHz between the YD(•) radical and Mn(2+) ion was observed using the pulsed electron-electron double resonance (PELDOR) technique, and the Mn(2+) ion was bound to one apo-PS II in the absence and presence of Ca(2+). PELDOR signals were calculated using the previously determined spin distribution on the YD(•) radical and its known position in the crystal structure, assuming that the specific Mn(2+) site was located in the oxygen evolving complex. The results show that the high-affinity Mn(2+) site is located at the position denoted by Mn4(A) in the native crystal structure. The Mn(2+) is coordinated with axial ligands Asp170 and Glu333 in the D1 polypeptide.
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http://dx.doi.org/10.1021/acs.jpcb.5b03994DOI Listing
August 2015

Site-directed spin labeling-electron spin resonance mapping of the residues of cyanobacterial clock protein KaiA that are affected by KaiA-KaiC interaction.

Genes Cells 2014 Apr 4;19(4):297-324. Epub 2014 Feb 4.

Center for Gene Research, Nagoya University, Furo, Chikusa, Nagoya, Aichi, 464-8602, Japan; Division of Biological Science, Graduate School of Science, Osaka University, Machikaneyama, Toyonaka, Osaka, 560-0043, Japan.

The cyanobacterial clock proteins KaiA, KaiB and KaiC interact with each other to generate circadian oscillations. We have identified the residues of the KaiA homodimer affected through association with hexameric KaiC (KaiC6mer) using a spin-label-tagged KaiA C-terminal domain protein (KaiAc) and performing electron spin resonance (ESR) analysis. Cys substitution and/or the attachment of a spin label to residues located at the bottom area of the KaiAc concave surface, a KaiC-binding groove, hindered the association of KaiAc with KaiC6mer, suggesting that the groove likely mediates the interaction with KaiC6mer. The residues affected by KaiC6mer association were concentrated in the three areas: the concave surface, a lobe-like structure (a mobile lobe near the concave surface) and a region adjacent to both the concave surface and the mobile lobe. The distance between the two E254, D255, L258 and R252 residues located on the mobile lobe decreased after KaiC association, suggesting that the two mobile lobes approach each other during the interaction. Analyzing the molecular dynamics of KaiAc showed that these structural changes suggested by ESR analysis were possible. Furthermore, the analyses identified three asymmetries in KaiAc dynamic structures, which gave us a possible explanation of an asymmetric association of KaiAc with KaiC6mer.
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http://dx.doi.org/10.1111/gtc.12130DOI Listing
April 2014

Effects of the rates of pseudo-spontaneous spikes generated by electric stimuli on information transmission in an auditory nerve fiber model.

Annu Int Conf IEEE Eng Med Biol Soc 2013 ;2013:5246-9

In this study, the effects of the rate of pseudo-spontaneous spikes on information transmission of the spike trains in response to the electric pulsatile stimulus currents in an auditory nerve fiber (ANF) model is investigated through computer simulation. The pseudo-spontaneous spikes can be generated by high rate pulsatile electric stimuli, making it possible to efficiently encode sound stimuli into the spike trains of the ANF in cochlear prostheses. In this investigation, the information rate of the spike trains in response to sinusoidally modulated pulsatile electric stimuli was estimated as the amplitude of the pulsatile electric stimuli (the rate of pseudo-spontaneous spikes) was varied. The results show that the information rates increased, reached a maximum, and then decreased, in several different values of modulation depth, as the rate of pseudo-spontaneous spikes increased. This may imply a resonance phenomenon dependent on the rate of pseudo-spontaneous spikes generated by electric stimuli in the ANF model. These findings may play a key role in the design of better cochlear prostheses.
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http://dx.doi.org/10.1109/EMBC.2013.6610732DOI Listing
August 2015

Reverse stochastic resonance in a hippocampal CA1 neuron model.

Annu Int Conf IEEE Eng Med Biol Soc 2013 ;2013:5242-5

Stochastic resonance (SR) is a ubiquitous and counter- intuitive phenomenon whereby the addition of noise to a non-linear system can improve the detection of sub-threshold signals. The "signal" is normally periodic or deterministic whereas the "noise" is normally stochastic. However, in neural systems, signals are often stochastic. Moreover, periodic signals are applied near neurons to control neural excitability (i.e. deep brain stimulation). We therefore tested the hypothesis that a quasi-periodic signal applied to a neural network could enhance the detection of a stochastic neural signal (reverse stochastic resonance). Using computational methods, a CA1 hippocampal neuron was simulated and a Poisson distributed subthreshold synaptic input ("signal") was applied to the synaptic terminals. A periodic or quasi periodic pulse train at various frequencies ("noise") was applied to an extracellular electrode located near the neuron. The mutual information and information transfer rate between the output and input of the neuron were calculated. The results display the signature of stochastic resonance with information transfer reaching a maximum value for increasing power (or frequency) of the "noise". This result shows that periodic signals applied extracellularly can improve the detection of subthreshold stochastic neural signals. The optimum frequency (110 Hz) is similar to that used in patients with Parkinson's suggesting that this phenomenon could play a role in the therapeutic effect of high frequency stimulation.
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http://dx.doi.org/10.1109/EMBC.2013.6610731DOI Listing
August 2015

Highly resolved proton matrix ENDOR of oriented photosystem II membranes in the S2 state.

Biochim Biophys Acta 2013 Oct 14;1827(10):1165-73. Epub 2013 Jun 14.

Division of Materials Science (Physics), Graduate School of Science, Nagoya University, Furocho, Chikusa, Nagoya 464-8602, Japan.

Proton matrix ENDOR was performed to investigate the protons close to the manganese cluster in oriented samples of photosystem II (PS II). Eight pairs of ENDOR signals were detected in oriented PS II membranes. At an angle of θ=0° between the membrane normal vector n and the external field H0, five pairs of ENDOR signals were exchangeable in D2O medium and three pairs were not exchangeable in D2O medium. The hyperfine splitting of 3.60MHz at θ=0° increased to 3.80MHz at θ=90°. The non-exchangeable signals with 1.73MHz hyperfine splitting at θ=0°, which were assigned to a proton in an amino acid residue, were not detected at θ=90° in oriented PS II or in non-oriented PS II. Highly resolved spectra show that only limited numbers of protons were detected by CW-ENDOR spectra, although many protons were located near the CaMn4O5 cluster. The detected exchangeable protons were proposed to arise from the protons belonging to the water molecules, labeled W1-W4 in the 1.9Å crystal structure, directly ligated to the CaMn4O5 cluster, and nearby amino-acid residue.
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http://dx.doi.org/10.1016/j.bbabio.2013.06.001DOI Listing
October 2013

Effects of rates of spontaneous synaptic vesicle secretions in inner hair cells on information transmission in an auditory nerve fiber model.

Annu Int Conf IEEE Eng Med Biol Soc 2012 ;2012:2993-6

Graduate School of Engineering, Kanto Gakuin University, 1-50-1 Mutsuura E., Kanazawa-ku, Yokohama 236-8501, Japan.

In this article, we investigate how the rates of spontaneous synaptic vesicle secretions affect information transmission of the spike trains in response to the inner hair cell (IHC) synaptic currents in an auditory nerve fiber (ANF) model through computer simulations. The IHC synaptic currents were modeled by a filtered inhomogeneous Poisson process modulated with sinusoidal functions, while the stochastic ion channel model was incorporated into each node of Ranvier in the ANF model with spiral ganglion. The information rates were estimated from the entropies of the inter-spike intervals of the spike trains to evaluate information transmission in the ANF model. The results show that the information rates increased, reached a maximum, and then decreased as the rate of spontaneous secretion increased, implying a resonance phenomenon dependent on the rate of spontaneous IHC synaptic secretions. In conclusion, this phenomenon similar to the regular stochastic resonance may be observed due to that spontaneous IHC synaptic secretions may act as an origin of fluctuation or noise, and these findings may play a key role in the design of better auditory prostheses.
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http://dx.doi.org/10.1109/EMBC.2012.6346593DOI Listing
August 2013

An influence of spontaneous spike rates on information transmission in a spherical bushy neuron model with stochastic ion channels.

Annu Int Conf IEEE Eng Med Biol Soc 2012 ;2012:1370-3

Graduate School of Engineering, Kanto Gakuin University, 1-50-1, Mutsuura E., Kanazawa-ku Yokohama 236-8501, Japan.

This article presents an effect of spontaneous spike firing rates on information transmission of the spike trains in a spherical bushy neuron model of antero-ventral cochlear nuclei. In computer simulations, the synaptic current stimuli ascending from auditory nerve fibers (ANFs) were modeled by a filtered inhomogeneous Poisson process modulated with sinusoidal functions, while the stochastic sodium and stochastic high- and low-threshold potassium channels were incorporated into a single compartment model of the soma in spherical bushy neurons. The information rates were estimated from the entropies of the inter-spike intervals of the spike trains to quantitatively evaluate information transmission in the spherical busy neuron model. The results show that the information rates increased, reached a maximum, and then decreased as the rate of spontaneous spikes from the ANFs increased, implying a resonance phenomenon dependent on the rate of spontaneous spikes from ANFs. In conclusion, this phenomenon similar to the stochastic resonance would be observed due to that spontaneous random spike firings coming from auditory nerves may act as an origin of fluctuation or noise, and these findings may play a key role in the design of better auditory prostheses.
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http://dx.doi.org/10.1109/EMBC.2012.6346193DOI Listing
August 2013

Electronic structure of S(2) state of the oxygen-evolving complex of photosystem II studied by PELDOR.

Biochim Biophys Acta 2013 Mar 8;1827(3):438-45. Epub 2013 Jan 8.

Graduate school of Science, Nagoya University, Chikusa, Nagoya, Japan.

Photosynthetic water splitting is catalyzed by a Mn(4)CaO(5) cluster in photosystem II, whose structure was recently determined at a resolution of 1.9Å [Umena, Y. et al. 2011, Nature, 473:55-60]. To determine the electronic structure of the Mn(4)CaO(5) cluster, pulsed electron-electron double resonance (PELDOR) measurements were performed for the tyrosine residue Y(D)() and S(2) state signals with non-oriented and oriented photosystem II (PS II) samples. Based on these measurements, the spin density distributions were calculated by comparing with the experimental results. The best fitting parameters were obtained with a model in which Mn1 has a large positive projection, Mn3 has a small positive projection, and Mn2 and Mn4 have negative projections (the numbering of Mni (i=1-4) is based on the crystal structure at a 1.9Å resolution), which yielded spin projections of 1.97, -1.20, 1.19 and -0.96 for Mn1-4 ions. The results show that the Mn1 ion, which is coordinated by H332, D342 and E189, has a valence of Mn(III) in the S(2) state. The sign of the exchange interactions J(13) is positive, and the other signs are negative.
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http://dx.doi.org/10.1016/j.bbabio.2012.12.011DOI Listing
March 2013

Aquaporin AqpZ is involved in cell volume regulation and sensitivity to osmotic stress in Synechocystis sp. strain PCC 6803.

J Bacteriol 2012 Dec 5;194(24):6828-36. Epub 2012 Oct 5.

Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama, Sendai, Japan.

The moderately halotolerant cyanobacterium Synechocystis sp. strain PCC 6803 contains a plasma membrane aquaporin, AqpZ. We previously reported that AqpZ plays a role in glucose metabolism under photomixotrophic growth conditions, suggesting involvement of AqpZ in cytosolic osmolarity homeostasis. To further elucidate the physiological role of AqpZ, we have studied its gene expression profile and its function in Synechocystis. The expression level of aqpZ was regulated by the circadian clock. AqpZ activity was insensitive to mercury in Xenopus oocytes and in Synechocystis, indicating that the AqpZ can be categorized as a mercury-insensitive aquaporin. Stopped-flow light-scattering spectrophotometry showed that addition of sorbitol and NaCl led to a slower decrease in cell volume of the Synechocystis ΔaqpZ strain than the wild type. The ΔaqpZ cells were more tolerant to hyperosmotic shock by sorbitol than the wild type. Consistent with this, recovery of oxygen evolution after a hyperosmotic shock by sorbitol was faster in the ΔaqpZ strain than in the wild type. In contrast, NaCl stress had only a small effect on oxygen evolution. The amount of AqpZ protein remained unchanged by the addition of sorbitol but decreased after addition of NaCl. This decrease is likely to be a mechanism to alleviate the effects of high salinity on the cells. Our results indicate that Synechocystis AqpZ functions as a water transport system that responds to daily oscillations of intracellular osmolarity.
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http://dx.doi.org/10.1128/JB.01665-12DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3510584PMC
December 2012

Stochastic resonance with a mixture of sub-and supra-threshold stimuli in a population of neuron models.

Annu Int Conf IEEE Eng Med Biol Soc 2011 ;2011:7328-31

Institute of Science and Technology, Kanto Gakuin University, 1-50-1 Mutsuura E, Kanazawa-ku, Yokohama 236-8501, Japan. gutch

This paper presents a novel type of stochastic resonance (SR) with a mixture of sub- and supra-threshold stimuli in a population of neuron models beyond regular SR and Supra-threshold SR (SSR) phenomena. We investigate through computer simulations if the novel type of SR can be observed or not, using the mutual information (MI) estimated from a population of neural spike trains as an index of information transmission. Computer simulations showed that the MI had a typical type of SR curves, even when the balance between sub-and supra-threshold stimuli was varied, suggesting the novel type of SR. Moreover, the peak of MI increased as the balance of supra-threshold stimuli got stronger, i.e., as the situation was getting close to the SSR from the regular SR. This finding could accelerate our understanding about how fluctuations play a role in processing information carried by a mixture of sub-and supra-threshold stimuli.
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http://dx.doi.org/10.1109/IEMBS.2011.6091709DOI Listing
August 2012

Nonselective excitation of pulsed ELDOR using multi-frequency microwaves.

J Magn Reson 2011 Dec 17;213(1):200-5. Epub 2011 Sep 17.

Division of Material Science (Physics), Graduate School of Science, Nagoya University, Furo, Chikusa, Nagoya 464-8602, Japan.

The use of a polychromatic microwave pulse to expand the pumping bandwidth in pulsed electron-electron double resonance (PELDOR) was investigated. The pumping pulse was applied in resonance with the broad (∼100 mT) electron paramagnetic resonance (EPR) signal of the manganese cluster of photosystem II in the S2 state. The observation pulses were in resonance with the narrow EPR signal of the tyrosine radical, YD·. It was found that in the case of the polychromatic pumping pulse containing five harmonics with the microwave frequencies between 8.5 and 10.5 GHz the PELDOR effect corresponding to the dipole interaction between the Mn cluster and YD· was about 2.9 times larger than that achieved with a monochromatic pulse. In addition to the dipolar modulation, the nuclear modulation effects were observed. The effects could be suppressed by averaging the PELDOR trace over the time interval between the observation microwave pulses. The polychromatic excitation technique described will be useful for improving the PELDOR sensitivity in the measurements of long distances in biological samples, where the pair consists of a radical with a narrow EPR spectrum and slow phase relaxation, and a metal center that has a broad EPR spectrum and a short phase relaxation time.
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http://dx.doi.org/10.1016/j.jmr.2011.09.034DOI Listing
December 2011

Monitoring the aggregation processes of amyloid-β using a spin-labeled, fluorescent nitroxyl radical.

Chem Commun (Camb) 2011 May 25;47(17):5070-2. Epub 2011 Mar 25.

Department of Bio-functional Science, Kyushu University, 3-1-1 Maidashi, Fukuoka, Japan.

Amyloid nitroxyl radical (nitroxide) ligands were used to detect amyloid-β fibrils, the main constituents of senile plaques in Alzheimer's disease, using anisotropic ESR spectra, and were found to affect the aggregation process due to the radical functionality. These compounds have great potential as novel and multifunctional probes, combining spin labels, spin probes, and fluorescence probes.
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http://dx.doi.org/10.1039/c0cc05764aDOI Listing
May 2011

Stochastic resonance can enhance information transmission in neural networks.

IEEE Trans Biomed Eng 2011 Jul 24;58(7):1950-8. Epub 2011 Mar 24.

Institute of Science and Technology, Kanto Gakuin University, Yokohama, 236-8501, Japan.

Stochastic resonance (SR) is a noise-induced phenomenon whereby signal detection can be improved by the addition of background noise in nonlinear systems. SR can also improve the transmission of information within single neurons. Since information processing in the brain is carried out by neural networks and noise is present throughout the brain, the hypothesis that noise and coupling play an important role in the control of information processing within a population of neurons to control was tested. Using computer simulations, we investigate the effect of noise on the transmission of information in an array of neurons, known as array-enhanced SR (AESR) in an interconnected population of hippocampal neurons. A subthreshold synaptic current (signal) modeled by a filtered homogeneous Poisson process was applied to a distal position in each of the apical dendrites, while background synaptic signals (uncorrelated noise) were presented to the midpoint in the basal dendrite. The transmembrane potentials were recorded in each cell of an array of CA1 neuron models, in order to determine spike firing times and to estimate the total and noise entropies from the spike firing times. The results show that the mutual information is maximized for a specific amplitude of uncorrelated noise, implying the presence of AESR. The results also show that the maximum mutual information increases with increased numbers of neurons and the strength of connections. Moreover, the relative levels of excitation and inhibition modulate the mutual information transfer. It is concluded that uncorrelated noise can enhance information transmission of subthreshold synaptic input currents in a population of hippocampal CA1 neuron models. Therefore, endogenous neural noise could play an important role in neural tissue by modulating the transfer of information across the network.
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http://dx.doi.org/10.1109/TBME.2011.2126571DOI Listing
July 2011

Interaction and inhibitory effect of ammonium cation in the oxygen evolving center of photosystem II.

Biochemistry 2011 Apr 3;50(13):2506-14. Epub 2011 Mar 3.

Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.

Photosynthetic O(2) evolution takes place at the Mn cluster in photosystem II (PSII) by oxidation of water. It has been proposed that ammonia, one of water analogues, functions as an inhibitor of O(2) evolution at alkaline pH. However, the detailed mechanism of inhibition has not been understood yet. In this study, we investigated the mechanism of ammonia inhibition by examining the NH(4)Cl-induced inhibition of O(2) evolution in a wide pH range (pH 5.0-8.0) and by detecting the interaction site using Fourier transform infrared (FTIR) spectroscopy. In addition to intact PSII membranes from spinach, PSII membranes depleted of the PsbP and PsbQ extrinsic proteins were used as samples to avoid the effect of the release of these proteins by salt treatments. In both types of samples, oxygen evolution activity decreased by approximately 40% by addition of 100 mM NH(4)Cl in the range of pH 5.0-8.0. The presence of inhibition at acidic pH without significant pH dependence strongly suggests that NH(4)(+) cation functions as a major inhibitor in the acidic pH region, where neutral NH(3) scarcely exists in the buffer. The NH(4)Cl treatment at pH 6.5 and 5.5 induced prominent changes in the COO(-) stretching regions in FTIR difference spectra upon the S(1) → S(2) transition measured at 283 K. The NH(4)Cl concentration dependence of the amplitude of the spectral changes showed a good correlation with that of the inhibition of O(2) evolution. From this observation, it is proposed that NH(4)(+) cation interacts with carboxylate groups coupled to the Mn cluster as direct ligands or proton transfer mediators, causing inhibition of the O(2) evolving reaction.
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http://dx.doi.org/10.1021/bi101952gDOI Listing
April 2011

Unique biogenesis of high-molecular mass multimeric metalloenzyme nitrile hydratase: intermediates and a proposed mechanism for self-subunit swapping maturation.

Biochemistry 2010 Nov;49(44):9638-48

Institute of Applied Biochemistry and Graduate School of Life and Environmental Sciences, The University of Tsukuba, Ibaraki, Japan.

Rhodococcus rhodochrous J1 produces high- and low-molecular mass nitrile hydratases (H-NHase and L-NHase, respectively), depending on the inducer. The incorporation of cobalt into L-NHase has been found to depend on the α-subunit exchange between cobalt-free L-NHase (apo-L-NHase) and its cobalt-containing mediator, NhlAE (holo-NhlAE), this novel mode of post-translational maturation having been named self-subunit swapping and NhlE having been recognized as a self-subunit swapping chaperone. We discovered an H-NHase maturation mediator, NhhAG, consisting of NhhG and the α-subunit of H-NHase. The incorporation of cobalt into H-NHase was confirmed to be dependent on self-subunit swapping. For the first time, particles larger than apo-H-NHase were observed during the swapping process via dynamic light scattering measurements, suggesting the formation of intermediate complexes. On the basis of these findings, we initially proposed a possible mechanism for self-subunit swapping. Electron paramagnetic resonance analysis demonstrated that the coordination environment of a cobalt ion in holo-NhhAG is subtly different from that in H-NHase. Cobalt is inserted into cobalt-free NhhAG (apo-NhhAG) but not into apo-H-NHase, suggesting that NhhG functions not only as a self-subunit swapping chaperone but also as a metallochaperone. In addition, α-subunit swapping did not occur between apo-L-NHase and holo-NhhAG or between apo-H-NHase and holo-NhlAE in vitro. These findings revealed that self-subunit swapping is a subunit-specific reaction.
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http://dx.doi.org/10.1021/bi100651vDOI Listing
November 2010
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