Japan Science and Technology Corporation JST

Saitama, Japan

Japan Science and Technology Corporation JST

Saitama, Japan
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Taniguchi Y.,Japan Advanced Institute of Science and Technology | Khatri B.S.,University of Edinburgh | Brockwell D.J.,University of Leeds | Paci E.,University of Leeds | And 2 more authors.
Biophysical Journal | Year: 2010

The motor protein myosin II plays a crucial role in muscle contraction. The mechanical properties of its coiled-coil region, the myosin rod, are important for effective force transduction during muscle function. Previous studies have investigated the static elastic response of the myosin rod. However, analogous to the study of macroscopic complex fluids, how myosin will respond to physiological time-dependent loads can only be understood from its viscoelastic response. Here, we apply atomic force microscopy using a magnetically driven oscillating cantilever to measure the dissipative properties of single myosin rods that provide unique dynamical information about the coiled-coil structure as a function of force. We find that the friction constant of the single myosin rod has a highly nontrivial variation with force; in particular, the single-molecule friction constant is reduced dramatically and increases again as it passes through the coiled-uncoiled transition. This is a direct indication of a large freeenergy barrier to uncoiling, which may be related to a fine-tuned dynamic mechanosignaling response to large and unexpected physiological loads. Further, from the critical force at which the minimum in friction occurs we determine the asymmetry of the bistable landscape that controls uncoiling of the coiled coil. This work highlights the sensitivity of the dissipative signal in force unfolding to dynamic molecular structure that is hidden to the elastic signal. © 2010 by the Biophysical Society.

Mitome N.,Tokyo Institute of Technology | Ono S.,Tokyo Institute of Technology | Sato H.,Tokyo Institute of Technology | Suzuki T.,Japan Science and Technology Corporation JST | And 4 more authors.
Biochemical Journal | Year: 2010

In FoF1 (FoF1-ATP synthase), proton translocation through Fo drives rotation of the oligomer ring of Fo-c subunits (c-ring) relative to Fo-a. Previous reports have indicated that a conserved arginine residue in Fo-a plays a critical role in the proton transfer at the Fo-a/c-ring interface. Indeed, we show in the present study that thermophilic F oF1s with substitution of this arginine (aR169) to other residues cannot catalyse proton-coupled reactions. However, mutants with substitution of this arginine residue by a small (glycine, alanine, valine) or acidic (glutamate) residue mediate the passive proton translocation. This translocation requires an essential carboxy group of Fo-c (cE56) since the second mutation (cE56Q) blocks the translocation. Rotation of the c-ring is not necessary because the same arginine mutants of the 'rotation-impossible' (c10-a)FoF1, in which the c-ring and Fo-a are fused to a single polypeptide, also exhibits the passive proton translocation. The mutant (aR169G/Q217R), in which the arginine residue is transferred to putatively the same topological position in the F o-a structure, can block the passive proton translocation. Thus the conserved arginine residue in Fo-a ensures proton-coupled c-ring rotation by preventing a futile proton shortcut. © The Authors.

Suzuki T.,Waseda University | Suzuki T.,Japan Science and Technology Corporation JST | Suzuki T.,Tokyo Institute of Technology | Tanaka K.,Japan Science and Technology Corporation JST | And 7 more authors.
Nature Chemical Biology | Year: 2014

The rotary motor enzyme F1-ATPase (F1) is a catalytic subcomplex of FoF1-ATP synthase that produces most of the ATP in respiring cells. Chemomechanical coupling has been studied extensively for bacterial F1 but very little for mitochondrial F1. Here we report ATP-driven rotation of human mitochondrial F1. A rotor-shaft γ-subunit in the stator α3β3 ring rotates 120° per ATP with three catalytic steps: ATP binding to one b-subunit at 0°, inorganic phosphate (Pi) release from another β-subunit at 65° and ATP hydrolysis on the third β-subunit at 90°. Rotation is often interrupted at 90° by persistent ADP binding and is stalled at 65° by a specific inhibitor azide. A mitochondrial endogenous inhibitor for FoF1-ATP synthase, IF1, blocks rotation at 90°. These features differ from those of bacterial F1, in which both ATP hydrolysis and Pi release occur at around 80°, demonstrating that chemomechanical coupling angles of the g-subunit are tuned during evolution. © 2014 Nature America, Inc. All rights reserved.

Shirakihara Y.,National Institute of Genetics | Shiratori A.,National Institute of Genetics | Tanikawa H.,National Institute of Genetics | Nakasako M.,University of Tokyo | And 7 more authors.
FEBS Journal | Year: 2015

F1-ATPase (F1) is the catalytic sector in FoF1-ATP synthase that is responsible for ATP production in living cells. In catalysis, its three catalytic β-subunits undergo nucleotide occupancy-dependent and concerted open-close conformational changes that are accompanied by rotation of the γ-subunit. Bacterial and chloroplast F1 are inhibited by their own ε-subunit. In the ε-inhibited Escherichia coli F1 structure, the ε-subunit stabilizes the overall conformation (half-closed, closed, open) of the β-subunits by inserting its C-terminal helix into the α3β3 cavity. The structure of ε-inhibited thermophilic F1 is similar to that of E. coli F1, showing a similar conformation of the ε-subunit, but the thermophilic ε-subunit stabilizes another unique overall conformation (open, closed, open) of the β-subunits. The ε-C-terminal helix 2 and hook are conserved between the two structures in interactions with target residues and in their positions. Rest of the ε-C-terminal domains are in quite different conformations and positions, and have different modes of interaction with targets. This region is thought to serve ε-inhibition differently. For inhibition, the ε-subunit contacts the second catches of some of the β- and α-subunits, the N- and C-terminal helices, and some of the Rossmann fold segments. Those contacts, as a whole, lead to positioning of those β- and α- second catches in ε-inhibition-specific positions, and prevent rotation of the γ-subunit. Some of the structural features are observed even in IF1 inhibition in mitochondrial F1. Database Structural data are available in the Worldwide Protein Data Bank database under the accession number 4XD7 Bacterial F1-ATPases including thermophilicF1 (TF1) are inhibited by its ε-subunit. The ε-inhibited TF1 structure is solved and compared with ε-inhibited E. coli F1 (EF1). TF1ε-subunit stabilizes one catalytic subunit's conformation in different form from EF1's. The ε-structures are different except their core regions, thus different inhibition properties. Bacterial ε-inhibition mechanism is now better understood in terms of structure. © 2015 FEBS.

Yoshida H.,Osaka University | Yoshida H.,Japan Science and Technology Corporation JST | Inoue K.,Osaka University | Kubo H.,Osaka University | Ozaki M.,Osaka University
Optical Materials Express | Year: 2013

We investigate the dispersibility of spherical gold nanoparticles in three phases of a chiral liquid crystal - blue phase I, blue phase II and the cholesteric phase - by UV-visible spectroscopy and optical microscopy. UV-visible spectroscopy revealed that a gradual red-shift and broadening of local surface plasmon resonance occur in the blue I and cholesteric phases. Moreover, optical microscopy revealed a clear difference in the aggregation behavior of nanoparticles depending on the phase, with uniform textures being observed in the blue II phase, and agglomerates forming in blue I and cholesteric phases. The difference in the dispersibility of nanoparticles is discussed in terms of the structure of each liquid crystal phase. © 2013 Optical Society of America.

Yabu S.,Osaka University | Tanaka Y.,Osaka University | Tagashira K.,Osaka University | Yoshida H.,Osaka University | And 4 more authors.
Optics Letters | Year: 2011

Polarization-independent refractive index (RI) modulation can be achieved in blue phase (BP) liquid crystals (LCs) by applying an electric field parallel to the direction of light transmission. One of the problems limiting the achievable tuning range is the field-induced phase transition to the cholesteric phase, which is birefringent and chiral. Here we report the RI modulation capabilities of gold nanoparticle-doped BPs I and II, and we show that field-induced BP-cholesteric transition is suppressed in nanoparticle-doped BP II. Because the LC remains optically isotropic even at high applied voltages, a larger RI tuning range can be achieved. © 2011 Optical Society of America.

Inoue Y.,Osaka University | Yoshida H.,Osaka University | Yoshida H.,Japan Science and Technology Corporation JST | Kubo H.,Osaka University | Ozaki M.,Osaka University
Advanced Optical Materials | Year: 2013

Fast (~10 μs) and deformation-free electro-optic tuning of a liquid crystal is reported, achieved by macroscopic alignment and switching of nanosized, pseudo-nematic domains. The tuning mode can be achieved by photopolymerizing a mesogenic monomer-liquid crystal mixture in the liquid crystal phase, and forming nanosized pores in the polymer matrix. This concept is particularly effective in liquid crystals with spontaneous structure-forming capabilities: here this concept is applied to a cholesteric liquid crystal and demonstrate scatter-free tuning of the Bragg reflection band. It can also lead to new device applications such as thin-film optical amplitude modulators and linear polarization rotators. Microsecond electro-optic tuning of the Bragg reflection band is demonstrated using a polymer-liquid crystal nanocomposite. Liquid crystalline order promotes formation of nanodomains in the composite, allowing scattering free-tuning of the effective refractive index without deforming the macroscopic helical structure. Nanoconfinement of the liquid crystal enables ultra-fast switching, reaching a decay time of 4 μs. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Yoshida H.,Osaka University | Yoshida H.,Japan Science and Technology Corporation JST | Yabu S.,Osaka University | Tone H.,Osaka University | And 2 more authors.
Applied Physics Express | Year: 2013

The electro-optic properties of cholesteric blue phase (BP) liquid crystals is investigated by two-beam interference microscopy. The technique can facilitate the evaluation of BP materials, since only a single measurement is required to determine the two important electro-optic coefficients, i.e., the Kerr and electrostriction coefficients, of BPs. Moreover, field-induced symmetry transitions can be observed microscopically, making this a powerful tool to investigate the structure-property relationship in BPs. Herein, we observe field-induced transitions from cubic BPs I and II to the centered tetragonal BP X, and investigate the influence of this transition on the Kerr coefficient. © 2013 The Japan Society of Applied Physics.

Inoue Y.,Osaka University | Yoshida H.,Osaka University | Yoshida H.,Japan Science and Technology Corporation JST | Inoue K.,Osaka University | And 4 more authors.
Advanced Materials | Year: 2011

Continuous tuning of lasing wavelength is achieved in cholesteric liquid crystal lasers by embedding a network of nanopores with an average size of 10 nm filled with liquid crystals inside a polymerized matrix with helical order. The device possesses both high transparency and a fast response time because the tuning is driven by local reorientation of the liquid crystal molecules in the nanopores. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Yoshida H.,Osaka University | Yoshida H.,Japan Science and Technology Corporation JST | Yabu S.,Osaka University | Tone H.,Osaka University | And 3 more authors.
Optical Materials Express | Year: 2014

The electro-optic Kerr effect in cubic blue phase liquid crystals comprises two components with different characteristic response times: one attributed to the primary (purely electro-optic) effect and another attributed to the secondary, or indirect (photoelastic) effect. Through simultaneous measurement of the polarized reflection spectrum and transmitted phase, we show that the contribution of the secondary electro-optic effect can be as large as 20% of the total change in refractive index, and that it is suppressed in the polymer-stabilized blue phase. Our results show the importance of stabilizing the lattice structure to realize blue-phase devices with fast response. © 2014 Optical Society of America.

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