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Articles by K. Yamamoto
Total Records ( 8 ) for K. Yamamoto
  R. J Scougall Vilchis , S Saku , H Kotake and K. Yamamoto

The aim of this study was to evaluate the influence of six self-etching primers (SEPs) on the shear/peel bond strength (SPBS) of orthodontic lingual buttons. A total of 150 extracted human premolars were randomly divided into six equal groups. In all groups, the lingual buttons were bonded with BeautyOrtho BondTM and the enamel was conditioned with the following—group I (Control): Primers A & BTM; group II: Transbond Plus SEPTM; group III: Clearfil Mega Bond FATM; group IV: AdheSETM; group V: Peak SE & Peak LC BondTM; and group VI: Bond ForceTM. The teeth were stored at 37°C for 24 hours and the SPBS was tested (0.5 mm/minute). The results were calculated in mega pascals (MPa) and statistically analysed [mean, standard deviation, Scheffè, analysis of variance (P < 0.05)]. The adhesive remnant index (ARI) was also evaluated and statistically analysed with a chi-square test.

All groups demonstrated higher SPBS than the force suggested as necessary to accomplish orthodontic tooth movement, except group IV (7.7 ± 1.7 MPa), which showed a significantly lower value than groups I (10.7 ± 2.4 MPa), II (11.3 ± 3.1 MPa), and V (10.9 ± 2.8 MPa). The values of groups III (9.9 ± 1.6 MPa) and VI (10.5 ± 1.6 MPa) were comparable with those of groups I and V. Significant differences (P < 0.05) were found among the groups in ARI scores.

The SPBS values of all groups could be clinically acceptable and lingual buttons might be successfully bonded with any of these SEPs except AdheSETM since that conditioner significantly influenced bond strength. As the SPBS was lower in all groups than the value at which enamel fractures have been found, a sound enamel surface might be left after removal of lingual buttons.

  H Ashida , A Miyake , M Kiyohara , J Wada , E Yoshida , H Kumagai , T Katayama and K. Yamamoto

Bifidobacteria are predominant bacteria present in the intestines of breast-fed infants and offer important health benefits for the host. Human milk oligosaccharides are one of the most important growth factors for bifidobacteria and are frequently fucosylated at their non-reducing termini. Previously, we identified 1,2--l-fucosidase (AfcA) belonging to the novel glycoside hydrolase (GH) family 95, from Bifidobacterium bifidum JCM1254 (Katayama T, Sakuma A, Kimura T, Makimura Y, Hiratake J, Sakata K, Yamanoi T, Kumagai H, Yamamoto K. 2004. Molecular cloning and characterization of Bifidobacterium bifidum 1,2--l-fucosidase (AfcA), a novel inverting glycosidase (glycoside hydrolase family 95). J Bacteriol. 186:4885–4893). Here, we identified a gene encoding a novel 1,3–1,4--l-fucosidase from the same strain and termed it afcB. The afcB gene encodes a 1493-amino acid polypeptide containing an N-terminal signal sequence, a GH29 -l-fucosidase domain, a carbohydrate binding module (CBM) 32 domain, a found-in-various-architectures (FIVAR) domain and a C-terminal transmembrane region, in this order. The recombinant enzyme was expressed in Escherichia coli and was characterized. The enzyme specifically released 1,3- and 1,4-linked fucosyl residues from 3-fucosyllactose, various Lewis blood group substances (a, b, x, and y types), and lacto-N-fucopentaose II and III. However, the enzyme did not act on glycoconjugates containing 1,2-fucosyl residue or on synthetic -fucoside (p-nitrophenyl--l-fucoside). The afcA and afcB genes were introduced into the B. longum 105-A strain, which has no intrinsic -l-fucosidase. The transformant carrying afcA could utilize 2'-fucosyllactose as the sole carbon source, whereas that carrying afcB was able to utilize 3-fucosyllactose and lacto-N-fucopentaose II. We suggest that AfcA and AfcB play essential roles in degrading 1,2- and 1,3/4-fucosylated milk oligosaccharides, respectively, and also glycoconjugates, in the gastrointestinal tracts.

  D Hu , Y Kamiya , K Totani , D Kamiya , N Kawasaki , D Yamaguchi , I Matsuo , N Matsumoto , Y Ito , K Kato and K. Yamamoto

Glucosidase II (GII) is a glycan-processing enzyme that trims two 1,3-linked glucose residues from N-glycan on newly synthesized glycoproteins. Trimming of the first 1,3-linked glucose from Glc2Man9GlcNAc2 (G2M9) is important for a glycoprotein to interact with calnexin/calreticulin (CNX/CRT), and cleavage of the innermost glucose from Glc1Man9GlcNAc2 (G1M9) sets glycoproteins free from the CNX/CRT cycle and allows them to proceed to the Golgi apparatus. GII is a heterodimeric complex consisting of a catalytic subunit (GII) and a tightly associated β subunit (GIIβ) that contains a mannose 6-phosphate receptor homology (MRH) domain. A recent study has suggested a possible involvement of the MRH domain of GIIβ (GIIβ-MRH) in the glucose trimming process via its putative sugar-binding activity. However, it remains unknown whether GIIβ-MRH possesses sugar-binding activity and, if so, what role this activity plays in the function of GII. Here, we demonstrate that human GIIβ-MRH binds to high-mannose-type glycans. Frontal affinity chromatography revealed that GIIβ-MRH binds most strongly to the glycans with the 1,2-linked mannobiose structure. GII with the mutant GIIβ that lost the sugar-binding activity of GIIβ-MRH hydrolyzes p-nitrophenyl--glucopyranoside, but the capacity to remove glucose residues from G1M9 and G2M9 is significantly decreased. Our results clearly demonstrate the capacity of the GIIβ-MRH to bind high-mannose-type glycans and its importance in efficient glucose trimming of N-glycans.

  K Mikami , D Yamaguchi , H Tateno , D Hu , S. Y Qin , N Kawasaki , M Yamada , N Matsumoto , J Hirabayashi , Y Ito and K. Yamamoto

Misfolded glycoproteins are translocated from the endoplasmic reticulum (ER) into the cytoplasm for proteasome-mediated degradation. OS-9 protein is thought to participate in ER-associated glycoprotein degradation (ERAD). The recombinant biotinylated mannose 6-phosphate receptor homology (MRH) domain of human OS-9 (OS-9MRH) together with six kinds of mutated OS-9MRH were prepared and mixed with R-phycoerythrin (PE)-labeled streptavidin to form tetramers (OS-9MRH-SA). The PE-labeled OS-9MRH-SA bound to HeLaS3 cells in a metal ion-independent manner through amino acid residues homologous to those participating in sugar binding of the cation-dependent mannose 6-phosphate receptor, and this binding was greatly increased by swainsonine, deoxymannojirimycin, or kifunensine treatment. N-Acetylglucosaminyltransferase I-deficient Lec1 cells, but not Lec2 or Lec8 cells, were also strongly bound by the tetramer. OS-9MRH-SA binding to the cells was strongly inhibited by Man1,6(Man1,3)Man1,6(Man1,3)Man and Man1,6Man. To further determine the specificity of native ligands for OS-9MRH, frontal affinity chromatography was performed using a wide variety of 92 different oligosaccharides. We found that several N-glycans containing terminal 1,6-linked mannose in the Man1,6(Man1,3)Man1,6(Man1,3)Man structure were good ligands for OS-9MRH, having Ka values of approximately 104 M–1 and that trimming of either an 1,6-linked mannose from the C-arm or an 1,3-linked mannose from the B-arm abrogated binding to OS-9MRH. An immunoprecipitation experiment demonstrated that the 1-antitrypsin variant nullHong Kong, but not wild-type 1-antitrypsin, selectively interacted with OS-9 in the cells in a sugar-dependent manner. These results suggest that trimming of the outermost 1,2-linked mannose on the C-arm is a critical process for misfolded proteins to enter ERAD.

  D Yamaguchi , D Hu , N Matsumoto and K. Yamamoto

XTP3-B is a soluble endoplasmic reticulum (ER)-resident protein containing two mannose-6-phosphate receptor homology (MRH) domains in its sequence. XTP3-B interacts with a membrane-associated ubiquitin ligase complex, and, therefore, is thought to participate in ER-associated degradation (ERAD). In this study, the recombinant human XTP3-B fused with IgG-Fc (XTP3-B-Fc), XTP3-B without an N-terminal MRH domain fused with IgG-Fc (XTP3-B1-Fc), or XTP3-B without a C-terminal MRH domain fused with IgG-Fc (XTP3-B2-Fc) were prepared. XTP3-B-Fc and XTP3-B1-Fc bound to Lec1 cells but not to CHO, Lec2, or Lec8 cells, while XTP3-B2-Fc did not bind to any of these cells. The binding of XTP3-B-Fc and XTP3-B1-Fc to Lec1 cells was abrogated by treatment of the cells with endo-β-N-acetylglucosaminidase H, Man1,6Man or Man1,6(Man1,3)Man1,6(Man1,3)Man, or by substitution of Arg428 or Tyr457 in the C-terminal MRH domain with alanine. Arg428 and Tyr457 are homologous to amino acids that mediate glycan binding by the cation-dependent mannose-6-phosphate receptor. An immunoprecipitation experiment using lysates of cells co-expressing wild-type 1-antitrypsin (AT), 1-antitrypsin variant nullHong Kong (ATNHK), and FLAG-tagged XTP3-B, or its mutants, demonstrated that ATNHK, but not AT, specifically co-precipitated with XTP3-B and XTP3-B1. The glycan-binding-deficient XTP3-B2 did not bind either AT or ATNHK. These results suggest that XTP3-B specifically binds to ATNHK, which is a well-known substrate of ERAD, via a C-terminal MRH domain in a glycan-dependent manner.

  Y Tani , T Funatsu , H Ashida , M Ito , S Itonori , M Sugita and K. Yamamoto

Hirsutella rhossiliensis, a nematophagous fungus belonging to the Ascomycota, is resistant to aureobasidin A (AbA). In this fungus, the biosynthetic pathway leading to mannosylinositolphosphoceramides, which is inhibited by AbA, was not detected. Instead, this fungus contains neutral complex glycosphingolipids (GSLs) and monoglycosylceramides. Except for monoglycosylceramides, neutral GSLs share a neogala-series core structure, Galβ1–6Galβ1-Cer. Among the GSLs of H. rhossiliensis, three novel GSLs with terminal Man and Glc residues on the sugar chain were elucidated. We analyzed GSL structure using compositional sugar, fatty acid, and sphingoid analyses, methylation analysis, matrix-assisted laser desorption ionization time-of-flight/mass spectrometry (MALDI-TOF MS), and 1H nuclear magnetic resonance spectroscopy (NMR). The following structures were determined: Man1–3Galβ1–6Galβ1–6Galβ1-Cer; Glc1–2Galβ1–6Galβ1–6Galβ1-Cer; and Man1–3Galβ1–6(Glc1–4)Galβ1–6Galβ1-Cer. In the ceramides, the fatty acids were predominantly saturated h24:0-acids and the sphingoids were predominately t18:0- or t18:1-sphingoids. In contrast, the ceramides of Glcβ1-Cer contained d18:2- and d19:2-sphingoids. These findings indicate the presence of a novel biosynthetic pathway of neogala-series GSLs in fungi.

  M Miwa , T Horimoto , M Kiyohara , T Katayama , M Kitaoka , H Ashida and K. Yamamoto

Bifidobacteria are predominant in the intestines of breast-fed infants and offer health benefits to the host. Human milk oligosaccharides (HMOs) are considered to be one of the most important growth factors for intestinal bifidobacteria. HMOs contain two major structures of core tetrasaccharide: lacto-N-tetraose (Galβ1-3GlcNAcβ1-3Galβ1-4Glc; type 1 chain) and lacto-N-neotetraose (Galβ1-4GlcNAcβ1-3Galβ1-4Glc; type 2 chain). We previously identified the unique metabolic pathway for lacto-N-tetraose in Bifidobacterium bifidum. Here, we clarified the degradation pathway for lacto-N-neotetraose in the same bifidobacteria. We cloned one β-galactosidase (BbgIII) and two β-N-acetylhexosaminidases (BbhI and BbhII), all of which are extracellular membrane-bound enzymes. The recombinant BbgIII hydrolyzed lacto-N-neotetraose into Gal and lacto-N-triose II, and furthermore the recombinant BbhI, but not BbhII, catalyzed the hydrolysis of lacto-N-triose II to GlcNAc and lactose. Since BbgIII and BbhI were highly specific for lacto-N-neotetraose and lacto-N-triose II, respectively, they may play essential roles in degrading the type 2 oligosaccharides in HMOs.

  K. Yamamoto , S. Oohori , H. Yamashita and S. Daido
  We have simulated the flow in a real cordierite DPF using the lattice Boltzmann method. Inner structure of the filter is analyzed by a 3D X-ray CT technique. Two processes of soot deposition for PM trap and soot combustion for filter regeneration process are considered. Especially, the effect of NO2 on the soot oxidation is examined, which is recently proposed as on-board regeneration system. The reaction rate has been determined based on previous experimental data. The estimated values of Arrhenius factor and activation energy are A = 146 1/s, E = 79.5 kJ/mol with NO2, and A = 1.20 1/s, E = 64.9 kJ/mol without NO2. Results show that, the flow field and pressure change inside the filter are clearly visualized. The pressure distribution depends on the non-uniformity of pore structure. The flow is largely changed with soot deposition, with higher pressure drop across the filter (filter back-pressure). The obtained correlation between total accumulated soot and the filter back-pressure is well in accordance with reported experimental results. In combustion simulation, the effect of NO2 addition to promote the soot oxidation is confirmed. These are useful information to develop the future regenerating DPF system.
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