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The Journal of Biochemistry
Year: 2010  |  Volume: 148  |  Issue: 5  |  Page No.: 603 - 616

Molecular characterization of plant acidic {alpha}-mannosidase, a member of glycosylhydrolase family 38, involved in the turnover of N-glycans during tomato fruit ripening

M. A Hossain, R Nakano, K Nakamura, M. T Hossain and Y. Kimura    

Abstract:

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.

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