Copy-DNA cloning and characterisation of a potato alpha-glucosidase: expression in Escherichia coli and effects of down-regulation in transgenic potato

Biocatalytic synthesis of 2-O-α-D-glucopyranosyl-L-ascorbic acid using an extracellular expressed α-glucosidase from Oryza sativa

BACKGROUND

2-O-α-D-Glucopyranosyl-L-ascorbic acid (AA-2G) is an important derivative of L-ascorbic acid (L-AA), which has the distinct advantages of non-reducibility, antioxidation, and reproducible decomposition into L-AA and glucose. Enzymatic synthesis is a preferred method for AA-2G production over alternative chemical synthesis owing to the regioselective glycosylation reaction. α-Glucosidase, an enzyme classed into O-glycoside hydrolases, might be used in glycosylation reactions to synthesize AA-2G.

MAIN METHODS AND MAJOR RESULTS

Here, an α-glucosidase from Oryza sativa was heterologously produced in Pichia pastoris GS115 and used for biosynthesis of AA-2G with few intermediates and byproducts. The extracellular recombinant α-glucosidase (rAGL) reached 9.11 U mL^-1 after fed-batch cultivation for 102 h in a 5 L fermenter. The specific activity of purified rAGL is 49.83 U mg^-1 at 37°C and pH 4.0. The optimal temperature of rAGL was 65°C, and it was stable below 55°C. rAGL was active over the range of pH 3.0-7.0, with the maximal activity at pH 4.0. Under the condition of 37°C, pH 4.0, equimolar maltose and ascorbic acid sodium salt, 8.7 ± 0.4 g L^-1  of AA-2G was synthesized by rAGL.

CONCLUSIONS AND IMPLICATIONS

The production of rAGL in P. pastoris was proved to be beneficial in providing enough enzyme and promoting biocatalytic synthesis of AA-2G. These studies lay the basis for the industrial application of α-glucosidase.

GRAPHICAL ABSTRACT LAY SUMMARY

2-O-α-D-Glucopyranosyl-L-ascorbic acid (AA-2G) is an important industrial derivative of L-ascorbic acid (L-AA), which has the distinct advantages of non-reducibility, antioxidation, and reproducible decomposition into L-AA and glucose. In this study, the authors characterized an α-glucosidase from Oryza sativa, which was recombinantly produced in Pichia pastoris GS115, and its potential for AA-2G production via transglycosylation of L-AA was investigated. These studies lay the basis for the industrial application of recombinant α-glucosidase.

Multiple forms of α-glucosidase in rice seeds (Oryza sativa L., var Nipponbare)

Two isoforms of alpha-glucosidases (ONG2-I and ONG2-II) were purified from dry rice seeds (Oryza sativa L., var Nipponbare). Both ONG2-I and ONG2-II were the gene products of ONG2 mRNA expressed in ripening seeds. Each enzyme consisted of two components of 6kDa-peptide and 88kDa-peptide encoded by this order in ONG2 cDNA (ong2), and generated by post-translational proteolysis. The 88kDa-peptide of ONG2-II had 10 additional N-terminal amino acids compared with the 88kDa-peptide of ONG2-I. The peptides between 6kDa and 88kDa components (26 amino acids for ONG2-I and 16 for ONG2-II) were removed by post-translational proteolysis. Proteolysis induced changes in adsorption and degradation of insoluble starch granules. We also obtained three alpha-glucosidase cDNAs (ong1, ong3, and ong4) from ripening seeds. The ONG1, ONG2, and ONG4 genes were situated in distinct locus of rice genome. The transcripts encoding ONG2 and ONG3 were generated by alternative splicing. Members of alpha-glucosidase multigene family are differentially expressed during ripening and germinating stages in rice.

Changes in alpha-xylosidase during intact and auxin-induced growth of pine hypocotyls

A complete cDNA from Pinus pinaster Aiton, potentially coding for an alpha-xylosidase able to remove the xylose residue from xyloglucan oligosaccharides, has been cloned. Its sequence was homologous to previously published alpha-xylosidase genes from Arabidopsis and nasturtium. The protein also showed the two signature regions of family 31 of glycosyl hydrolases. The gene expression level was quantified by competitive RT-PCR, under different growth conditions, throughout seedling development, in different regions along the hypocotyls and in auxin-treated hypocotyl segments, and related with growth capacity and alpha-xylosidase activity. A role of alpha-xylosidase in regulating the level of xyloglucan oligosaccharides within the apoplast is proposed. The action of an alpha-xylosidase removing the xylose residue, would make possible the action of a beta-glucosidase deblocking the xyloglucan oligosaccharide degradation and it could serve as a control point for the regulation of the apoplastic levels of xyloglucan oligosaccharides.