Shin-ichi Takata

Static inhomogeneities and dynamic fluctuations of temperature sensitive polymer gels

The static inhomogeneities and dynamic fluctuations in polymer gels have been studied by light scattering as a function of the gel preparation temperature, Tprep, and the cross-link density. The light scattered intensity of polymer gels was decomposed to two parts; the intensities due to the thermal fluctuations, IF, and the frozen inhomogeneities, IC. The analysis employing ensemble (··E) and time averaging (··T) of light scattered intensity disclosed that IFT (the thermal fluctuations) depends neither on the cross-link density nor the temperature of gel preparation, but on the temperature of observation. On the other hand, ICE (the frozen inhomogeneities) is a function of both temperatures at preparation and at observation. This clearly shows that gel is matter with dynamic fluctuations superimposed on the static frozen inhomogeneities. The latter are built-in inhomogeneities due to topological constraints of the gel by cross-linking formation.

In situ lattice strain mapping during tensile loading using the neutron transmission and diffraction methods

In this study, the change in internal lattice strain in an iron plate during tensile deformation was investigated by performing in situ measurements under applied force. The lattice strain was evaluated by neutron diffraction and Bragg-edge transmission. The neutron diffraction results showed that the averaged 110 lattice strain along the direction perpendicular to the applied force was between −422 and −109 × 10−6. The position dependence of the lattice strain and the change in the distribution of elastic strain in an iron plate with notches during tensile deformation was obtained by Bragg-edge transmission. It was also observed that, when the load increased over 30 kN, the area of plastic deformation increased around the positions of the notches.

Spatial arrangement and functional role of α subunits of proteasome activator PA28 in hetero-oligomeric form.

A major form of proteasome activator PA28 is a heteroheptamer composed of interferon-γ-inducible α and β subunits, which share approximately 50% amino acid identity and possess distinct insert loops. This activator forms a complex with the 20S proteasome and thereby stimulates proteasomal degradation of peptides in an ATP-independent manner, giving rise to smaller antigenic peptides presented by major histocompatibility complex class I molecules. In this study, we performed biophysical and biochemical characterization of the structure and function of the PA28 hetero-oligomer. Deuteration-assisted small-angle neutron scattering demonstrated three α and four β subunits are alternately arranged in the heptameric ring. In this arrangement, PA28 loops surround the central pore of the heptameric ring (site for peptide entry). Activating the 20S proteasome with a PA28 mutant that lacked the α subunit loops cleaved model substrates longer than a nonapeptide with better efficiency when compared to wild-type PA28. Based on these data, we hypothesize that the flexible PA28 loops act as gatekeepers, which function to select the length of peptide substrates to be transported between the proteolytic chamber and the extra-proteasomal medium.

The Design and q Resolution of the Small and Wide Angle Neutron Scattering Instrument (TAIKAN) in J-PARC

J-PARC Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan Research Center for Neutron Science and Technology, Comprehensive Research Organization for Science and Society (CROSS), Tokai, Ibaraki 319-1106, Japan J-PARC Center, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan Research Reactor Institute, Kyoto University (KURRI), Kumatori, Osaka 590-0494, Japan

Shape of α-crystallin analyzed by small-angle neutron scattering

The size and shape of aggregates of human recombinant αA-crystallin and αB-crystallin are investigated with small-angle neutron scattering and dynamic light scattering. At a bioactive temperature (310 K), both polypeptides form aggregates with almost the same size and shape. The αB-crystallin maintains an almost identical size and shape at 310 and 288 K, whereas the aggregate of αA-crystallin shows deformation at 288 K. This result suggests that at the lower temperature there is a difference in structural stability between the two aggregates of the polypeptides.

Size-tunable Confined Water in a Room Temperature Ionic Liquid

Department of Materials Science and Engineering, National Defense Academy, Yokosuka 239-8686, Japan Department of Applied Chemistry, National Defense Academy, Yokosuka 239-8686, Japan Department of Applied Chemistry, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan Research Center for Neutron Science and Technology, Comprehensive Research Organization for Science and Society (CROSS), IQBRC Bldg, 162-1 Shirakata, Tokai, Ibaraki 319-1106, Japan Japan Atomic Energy Agency, 2-4 Shirane Shirakata, Tokai, Ibaraki 319-1195, Japan

Contrast variation by dynamic nuclear polarization and time-of-flight small-angle neutron scattering. I. Application to industrial multi-component nanocomposites

Contrast variation small-angle neutron scattering by dynamic nuclear polarization is applied to industrial multi-component nanocomposites.

Dynamical Behavior of Hydration Water Molecules between Phospholipid Membranes

The dynamical behavior of hydration water sandwiched between 1,2-dimyristyl-sn-glycero-3-phosphocholine (DMPC) bilayers was investigated by quasi-elastic neutron scattering (QENS) in the range between 275 and 316 K, where the main transition temperature of DMPC is interposed. The results revealed that the hydration water could be categorized into three types of water: (1) free water, whose dynamical behavior is slightly different from that of bulk water; (2) loosely bound water, whose dynamical behavior is 1 order of magnitude slower than that of the free water; and (3) tightly bound water, whose dynamical behavior is comparable with that of DMPC molecules. The number of loosely bound and tightly bound water molecules per DMPC molecule monotonically decreased and increased with decreasing temperature, respectively, and the sum of these water molecules remained constant. The number of free water molecules per DMPC molecule was constant in the measured temperature range.

Development of a triplet magnetic lens system to focus a pulsed neutron beam

A triplet magnetic lens system composed of three sextupole-magnets and two spin flippers was constructed to focus pulsed neutrons in a wide wavelength range with same focal lengths. In this study, we performed a pulsed neutron beam focusing experiment with the system. The design of the system and the experimental results are shown and discussed.

Direct Evidence of Effect of Glycerol on Hydration and Helix-to-Sheet Transition of Myoglobin

By using wide-angle X-ray scattering (WAXS), small-angle neutron scattering, and theoretical scattering function simulation, we have clarified the effect of glycerol on both the thermal structure transition and the hydration-shell of myoglobin. At the glycerol concentration, ≤ ∼40 % v/v, the decreasing tendency in the maximum dimension and the radius of gyration was observed by X-ray scattering. The neutron scattering result using the inverse contrast variation method directly shows the preservation of the hydration-shell density at the concentration ≤ ∼40 % v/v. This phenomenon is reasonably explained by the preferential exclusion of glycerol from the protein surface to preserve the hydration shell, as suggested by the previous studies. While, at the concentration, ≥ 50 % v/v, the opposite tendency was observed. It suggests the preferential solvation (partial preferential penetration or replacement of glycerol into or with hydration-shell water surrounding the protein surface) occurs at the higher concentration. The observed WAXS scattering data covers the distinct hierarchical structural levels of myoglobin structure ranging from the tertiary structure to the secondary one. Therefore, we have clarified the effect of glycerol on the thermal structural stability myoglobin at different hierarchical structural levels separately. Against the temperature rise, the structural transition temperatures for all hierarchical structural levels were elevated. Especially, the tertiary structure of myoglobin was more stabilized compared with the internal-structure and the helix-to-cross transition. It suggests that the protective action of glycerol on protein structures essentially results from the preservation of the preferential hydration-shell of proteins.