Biomedical subjects

Takao Sato

Publications and source records attributed to Takao Sato.

10 recordsLinked to original sources

PubMed2004

Structure of bovine carbonic anhydrase II at 1.95 A resolution.

Carbonic anhydrase (CA) is a zinc-containing enzyme that catalyzes the reversible hydration of CO2 to HCO3-. In eukaryotes, the enzyme plays a role in various physiological functions, including interconversion between CO2 and HCO3- in intermediary metabolism, facilitated diffusion of CO2, pH homeostasis and ion transport. The structure of bovine carbonic anhydrase II (BCA II) has been determined by molecular replacement and refined to 1.95 A resolution by simulated-annealing and individual B-factor refinement. The final R factor for the BCA II structure was 19.4%. BCA II has a C-terminal knot structure similar to that observed in human CA II. It contains one zinc ion in the active site coordinated to three histidines and one putative water molecule in a tetrahedral geometry. The structure of BCA II reveals a probable alternative proton-wire pathway that differs from that of HCA II.

Animals↗

PubMed2003

Crystallization and X-ray analysis of the N-terminal core domain of a tumour-associated human DEAD-box RNA helicase, rck/p54.

The RCK gene was cloned on the basis of the t(11;14)(q23;q32) chromosome translocation observed in human B-cell lymphoma cell line RC-K8. This gene was found to be overexpressed in various kinds of tumours. The gene product, rck/p54, consisting of 472 amino-acid residues with molecular weight 53.2 kDa, belongs to the family of DEAD-box RNA helicases. Its ATP-dependent RNA-unwinding activity toward c-myc RNA molecules in vitro has recently been demonstrated. In the present study, limited proteolysis experiments of rck/p54 were used to truncate the N-terminal domain (residues 1-288; 31.8 kDa) of rck/p54, leading to successful crystallization of Nc-rck/p54, i.e. the N-terminal core domain (residues 70-288; 24.5 kDa) of rck/p54. Crystals of Nc-rck/p54 were grown to a size suitable for X-ray structure analysis using polyethylene glycol 3350 as the precipitant. The crystal belongs to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 65.5, b = 73.1, c = 84.8 A, and diffracts X-rays to beyond 2.0 A resolution.

Amino Acid Sequence↗

PubMed2003

A unique dye-decolorizing peroxidase, DyP, from Thanatephorus cucumeris Dec 1: heterologous expression, crystallization and preliminary X-ray analysis.

The dye-decolorizing peroxidase DyP is a key enzyme in the decolorizing fungus Thanatephorus cucumeris Dec 1 that degrades azo and antraquinone dyes. The gene dyp from T. cucumeris Dec 1, which has low homology to other peroxidase genes, was cloned and transformed into Aspergillus oryzae and glycosylated DyP was expressed at high levels. Purified DyP was deglycosylated using GST Endo F1 and then crystallized in a strong magnetic field (10 T) at 283 K using ammonium sulfate as precipitant. X-ray diffraction data to 2.96 A resolution collected from a native crystal at the Photon Factory (Tsukuba, Japan) showed that the crystal belonged to the hexagonal space group P6(5)22, with unit-cell parameters a = b = 136.15, c = 363.46 A. The asymmetric unit of the crystal contained four DyP molecules, with a corresponding Matthews coefficient (V(M)) of 2.50 A(3) Da(-1) and a solvent content of 51%. Heavy-atom derivatives of DyP have been obtained and electron-density maps have been calculated. The haem is visible and continuous electron density between the haem and protein clearly indicates the location of the proximal histidine ligand.

Aspergillus oryzae↗

PubMed2003

Azulene incorporation and release by hydrogel containing methacrylamide propyltrimenthylammonium chloride, and its application to soft contact lens.

We have developed the epoch-making contact lens that is equipped with drug delivery system. The hydrogels contain cationic functional group in its side chain were prepared with 2-hydroxyethyl methacylate (HEMA) and methacrylamide propyltrimethylammonium chloride (MAPTAC). The obtained hydrogel is capable to store the anionic drug such as azulene based on ion-exchange reaction. The incorporated anionic drug would be released in physiological condition. The size change of the hydrogel may occur before and after drug release, but we have discovered that the addition of anionic monomer such as methacrylic acid (MAA) and 2-methacryloxyethyl acid phosphate (MOEP) to the above-mentioned composition is effective to prevent the size change, indicating that this hydrogel has the possibility to be applied as a significant drug delivery system device.

Ammonium Chloride↗

PubMed2003

Structural insight into modest binding of a non-PXXP ligand to the signal transducing adaptor molecule-2 Src homology 3 domain.

Although some exceptional motifs have been identified, it is well known that the PXXP motif is the motif of ligand proteins generally recognized by the Src homology 3 (SH3) domain. SH3-ligand interactions are usually weak, with ordinary KD approximately 10 microM. The structural basis for a tight and specific association (KD = 0.24 microm) between Gads SH3 and a novel motif, PX(V/I)(D/N)RXXKP, was revealed in a previous structural analysis of the complex formed between them. In this paper, we report the crystal structure of the signal transducing adaptor molecule-2 (STAM2) SH3 domain in complex with a peptide with a novel motif derived from a ligand protein, UBPY. The derived KD value for this complex is 27 microM. The notable difference in affinity for these parallel complexes may be explained because the STAM2 SH3 structure does not provide a specificity pocket for binding, whereas the Gads SH3 structure does. Instead, the structure of STAM2 SH3 is analogous to that of Grb2 SH3 which, in addition to normal PXXP ligands, has also been shown to moderately recognize the novel motif discussed herein. Thus, the extremely tight interaction observed between Gads SH3 and the novel motif is caused not by an innate ability of the novel motif but rather by an evolutionary change in the Gads SH3 domain. Instead, SH3 domains of STAM2 and Grb2 retain the moderate characteristics of recognizing their ligand proteins like other SH3 domains for appropriate transient interactions between signaling molecules.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Reversed-phi perception with motion-defined motion stimuli.

Perception of reversed-phi with motion-defined motion (MDM) stimuli was examined while varying various parameters including eccentricity. For peripheral viewing, reversed-phi was observed at all displacements between 30 degrees and 135 degrees. The perception most prominent at 90 degrees, but was disrupted by dichoptic presentation. These results suggest operations of an energy-based motion system similar to the first-order motion system for luminance motion, which most likely resides at a relatively early level (cf. [Vision Res. 33 (1993) 533]). For central viewing, reversed motion was observed only for larger displacements. The perceived motion at smaller displacements was predominantly in the forward direction. Transition between the two modes occurred around 90 degrees displacement. In addition, this motion perception was not disrupted by dichoptic presentation. This indicated the operation of a polarity independent matching-based motion system residing at a higher-level. Thus, the results indicate the involvement of at least two separate mechanisms for MDM detection, and that there is a dominance shift between the two systems according to the eccentricity.

Contrast Sensitivity↗

PubMed2003

Attentional modulation of self-motion perception.

Attentional effects on self-motion perception (vection) were examined by using a large display in which vertical stripes containing upward or downward moving dots were interleaved to balance the total motion energy for the two directions. The dots moving in the same direction had the same colour, and subjects were asked to attend to one of the two colours. Vection was perceived in the direction opposite to that of non-attended motion. This indicates that non-attended visual motion dominates vection. The attentional effect was then compared with effects of relative depth. Clear attentional effects were again found when there was no relative depth between dots moving in opposite directions, but the effect of depth was much stronger for stimuli with a relative depth. Vection was mainly determined by motion in the far depth plane, although some attentional effects were evident even in this case. These results indicate that attentional modulation for vection exists, but that it is overridden when there is a relative depth between the two motion components.

Adult↗

PubMed2002

The 2.0 A crystal structure of catalase-peroxidase from Haloarcula marismortui.

Catalase-peroxidase is a member of the class I peroxidase superfamily. The enzyme exhibits both catalase and peroxidase activities to remove the harmful peroxide molecule from the living cell. The 2.0 A crystal structure of the catalase-peroxidase from Haloarcula marismortui (HmCP) reveals that the enzyme is a dimer of two identical subunits. Each subunit is composed of two structurally homologous domains with a topology similar to that of class I peroxidase. The active site of HmCP is in the N-terminal domain. Although the arrangement of the catalytic residues and the cofactor heme b in the active site is virtually identical to that of class I peroxidases, the heme moiety is buried inside the domain, similar to that in a typical catalase. In the vicinity of the active site, novel covalent bonds are formed among the side chains of three residues, including that of a tryptophan on the distal side of the heme. Together with the C-terminal domain, these covalent bonds fix two long loops on the surface of the enzyme that cover the substrate access channel to the active site. These features provide an explanation for the dual activities of this enzyme.

Amino Acid Sequence↗

PubMed2002

The effect of the poly(ethylene glycol) chain on surface exchange of rigid gas-permeable contact lenses.

PURPOSE: The SEED Company, Ltd. developed the novel SEED S-1, a rigid gas-permeable contact lens (RGPCL) with a hydrophilic monomer grafted onto its surface by polymerization. This article describes the use of the polymerized graft material poly(ethylene glycol) (PEG) used as a biomaterial, and characterizes the surface of the RGPCL. METHODS: The grafting of PEG onto a RGPCL was carried out by plasma treatment and polymerization, and the characteristics of the RGPCL surface were obtained by measuring the water equilibrium contact angle and the surface zeta potential. The zeta potential was measured using an electrophoretic light-scattering photometer. Furthermore, the characteristics of the interaction between the polymer surface and protein was obtained by observing the relationship of adsorption between the protein and lipids and the polymer surfaces. RESULTS: The RGPCL became hydrophilic with increasing ethylene glycol units when the graft was polymerized onto the otherwise hydrophobic surface. After the graft polymerization of PEG onto the RGPCL, the surface zeta potentials increased to a negative static surface with the increased addition of ethylene glycol units. Additionally, the amount of adsorption of protein and lipids were decreased, respectively, as the ethylene glycol chain increased in length. CONCLUSIONS: The hydrophobic surface of the RGPCL was changed to a hydrophilic surface by graft polymerization of PEG. This suggests that novel RGPCL surfaces can be designed by graft polymerization, using such ethylene glycol groups.

Biocompatible Materials↗

PubMed2002

Adaptation to relative and uniform motion.

We compared the discriminability of motion direction with a relative motion stimulus after prolonged exposure to relative or uniform motion. Experiment 1 showed that the velocity threshold for the relative motion test after relative motion exposure was higher than that after uniform motion exposure, whereas no such difference was found when we tested with a uniform motion stimulus. Experiment 2 showed that prolonged exposure to relative motion decreased the discriminability of speed differences more than exposure to uniform motion. These results suggest that the visual system's pathway for relative motion signals is different from that for uniform motion signals.

Adaptation, Physiological↗