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

• DOI: 10.1093/jb/mvq094
• Publication Date: 2010-08-26T21:14:08Z
• Authors: M. A. Hossain; R. Nakano; K. Nakamura; M. T. Hossain; Y. Kimura
• Keywords: Models, Molecular; 0301 basic medicine; 2. Zero hunger; 1-Deoxynojirimycin; Base Sequence; Swainsonine; Molecular Sequence Data; Temperature; Hydrogen-Ion Concentration; Recombinant Proteins; Substrate Specificity; 03 medical and health sciences; Solanum lycopersicum; Polysaccharides; alpha-Mannosidase; Fruit; Amino Acid Sequence; Cloning, Molecular; Lysosomes; Sequence Alignment; Phylogeny; Glycoproteins

It has been reported that acidic α-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 α-mannosidase activity and fruit maturation at the molecular level, we have already purified and characterized an α-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 α-mannosidase gene using the yeast-expression system. The α-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 α-mannosidase, like the native enzyme, could cleave α1-2, 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 α-mannosidase could be superimposed on those of tomato α-mannosidase, suggesting that active site conformation is highly conserved between plant acidic α-mannosidase and animal lysosomal α-mannosidase.