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Articles by T Imanaka
Total Records ( 3 ) for T Imanaka
  M. M Sira , T Yoshida , M Takeuchi , Y Kashiwayama , T Futatani , H Kanegane , A Sasahara , Y Ito , M Mizuguchi , T Imanaka and T. Miyawaki

Human colostrum contains many bioactive factors that must promote the development of intestinal mucosal immunity in infants. Especially, the presence of certain cytokines such as transforming growth factor (TGF)-β or IL-10 has been of great interest for IgA production as a function of mucosal immune response. In the present study, we attempted to investigate whether unidentified factors inducing generation of IgA-producing cells from naive B cells might exist in colostrum. For this purpose, colostrum samples were directly added to a culture consisting of naive B cells and dendritic cells from cord blood and CD40 ligand-transfected L cells, comparing with recombinant IL-10 (rIL-10) and/or rTGF-β. It was noted that most colostrum samples alone were able to induce IgA-secreting cells at higher levels than rIL-10 and/or rTGF-β. IgA-inducing activity of colostrum was abolished by neither anti-neutralizing mAbs against IL-10 nor TGF-β, though partially by anti-IL-6 mAb. We prepared partially purified fractions from both pooled colostrums with and without IgA-inducing activity and comparatively performed quantitative proteomic analysis by two-dimensional difference gel electrophoresis followed by liquid chromatography-mass spectrometry. As a result, syntenin-1 was identified as a candidate for IgA-inducing protein in colostrum. Western blot analysis indicated that levels of syntenin-1 in colostrum samples were correlated with their IgA-inducing activities. Moreover, we demonstrated that recombinant syntenin-1 could induce preferentially IgA production from naive B cells. These results suggest that syntenin-1 serves as one of IgA-inducing factors for B cells.

  Q Bashir , N Rashid , F Jamil , T Imanaka and M. Akhtar

l-Threonine dehydrogenase, a key enzyme in the l-threonine metabolism, catalyses the NAD+-dependent conversion of l-threonine to 2-amino-3-ketobutyrate, that non-enzymically decarboxylates to aminoacetone. A search of the genome sequence of hyperthermophilic archaeon, Thermococcus kodakaraensis revealed the presence of a closely related orthologue (TK0916) of archaeal and bacterial l-threonine dehydrogenase genes. Expression in Escherichia coli, purification and characterization of the TK0916 gene product revealed that this gene actually coded for a protein with high levels of l-threonine dehydrogenase activity (7.26 U mg–1). The enzyme exhibited highest activity at pH 12 and 90°C. The Km values for l-threonine and NAD+ at 50°C were 1.6 mM and 0.028 mM, respectively. The enzyme activity was dependent on divalent cations. The half-life of the enzyme was more than 2 h at 85°C and 24 min in boiling water. This is the most thermostable threonine dehydrogenase exhibiting optimal activity at the highest pH (12) reported to date. This is the first report on the characterization of a TDH from genus Thermococcus.

  S Iwashita , M Tsuchida , M Tsukuda , Y Yamashita , Y Emi , Y Kida , M Komori , Y Kashiwayama , T Imanaka and M. Sakaguchi

Most membrane proteins are recognized by a signal recognition particle and are cotranslationally targeted to the endoplasmic reticulum (ER) membrane, whereas almost all peroxisomal membrane proteins are posttranslationally targeted to the destination. Here we examined organelle-targeting properties of the N-terminal portions of the peroxisomal isoform of the ABC transporter PMP70 (ABCD3) using enhanced green fluorescent protein (EGFP) fusion. When the N-terminal 80 amino acid residue (N80)-segment preceding transmembrane segment (TM) 1 was deleted and the TM1–TM2 region was fused to EGFP, the TM1 segment induced ER-targeting and integration in COS cells. When the N80-segment was fused to EGFP, the fusion protein was targeted to the outer mitochondrial membrane. When both the N80-segment and the following TM1–TM2 region were present, the fusion located exclusively to the peroxisome. The full-length PMP70 molecule was clearly located in the ER in the absence of the N80-segment, even when multiple peroxisome-targeting signals were retained. We concluded that the TM1 segment possesses a sufficient ER-targeting function and that the N80-segment is critical for suppressing the ER-targeting function to allow the TM1–TM2 region to localize to the peroxisome. Cooperation of the organelle-targeting signals enables PMP70 to correctly target to peroxisomal membranes.

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