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Articles by Y. Kimura
Total Records ( 2 ) for Y. Kimura
  M. A Hossain , R Nakano , K Nakamura , M. T Hossain and Y. Kimura

It has been reported that acidic -mannosidase activity increases during tomato fruit ripening, suggesting the turnover of N-glycoproteins is deeply associated with fruit ripening. As part of a study to reveal the relationship between the plant -mannosidase activity and fruit maturation at the molecular level, we have already purified and characterized an -mannosidase from tomato fruit (Hossain et al., Biosci. Biotechnol. Biochem. 2009;73:140–146). In this article, we describe the identification and expression of the tomato acidic -mannosidase gene using the yeast-expression system. The -mannosidase-gene located at chomosome 6 is a 10 kb spanned containing 30 exons. The gene-encoded-protein is single polypeptide chain of 1,028 amino acids containing glycosyl hydrolase domain-38 with predicted molecular mass of 116 kDa. The recombinant enzyme showed maximum activity at pH 5.5, and was almost completely inhibited by both of 1-deoxymannojirimycin and swainsonine. The recombinant -mannosidase, like the native enzyme, could cleave 1-2, 1-3 and 1-6 mannosidic linkage from both high-mannose and truncated complex-type N-glycans. A molecular 3D modelling shows that catalytically important residues of animal lysosomal -mannosidase could be superimposed on those of tomato -mannosidase, suggesting that active site conformation is highly conserved between plant acidic -mannosidase and animal lysosomal -mannosidase.

  M Maeda , M Kimura and Y. Kimura

As a part of the study to reveal the biological significance of de-N-glycosylation in plants, we analysed the structural features of free N-glycans (FNGs) accumulated inside cells and secreted to the extracellular space using a rice cell culture system. The structural analysis of FNGs obtained from the intracellular fraction revealed that the high-mannose type N-glycans with one GlcNAc residue (GN1-type) occurred at a concentration of ~10 nmol/g, while the truncated complex type N-glycans with a N, N'-diacetylchitobiosyl unit (GN2-type) occurred at a concentration of ~1 nmol/g. This result suggested that two kinds of glycoenzymes, cytosolic endo-β-N-acetylglucosaminidase (ENGase) and intracellular acidic peptide:N-glycanse (PNGase), are involved in the production of FNGs in rice cell as well as in other plant cells. On the other hand, in the culture medium, Lewis a epitope-containing complex and high-mannose type FNGs with the N, N'-diacetylchitobiosyl unit were found, suggesting extracellular acidic PNGase to be involved in the release of N-glycans from folded/processed glycoproteins in extracellular space. Furthermore, in the culture medium, we found unusual GN1-FNGs that have a biantennary complex type structure harbouring the Lewis a epitope, suggesting cytosolic ENGase and golgi N-glycan-processing enzymes to be involved in the production of these plant complex type FNGs.

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