Design of chimeric levansucrases with improved transglycosylation activity.

Fructansucrases (FSs), including levansucrases and inulosucrases, are enzymes that synthesize fructose polymers from sucrose by the direct transfer of the fructosyl moiety to a growing polymer chain. These enzymes, particularly the single domain fructansucrases, also possess an important hydrolytic activity, which may account for as much as 70 to 80% of substrate conversion, depending on reaction conditions. Here, we report the construction of four chimeric levansucrases from SacB, a single domain levansucrase produced by Bacillus subtilis. Based on observations derived from the effect of domain deletion in both multidomain fructansucrases and glucansucrases, we attached different extensions to SacB. These extensions included the transitional domain and complete C-terminal domain of Leuconostoc citreum inulosucrase (IslA), Leuconostoc mesenteroides levansucrase (LevC), and a L. mesenteroides glucansucrase (DsrP). It was found that in some cases the hydrolytic activity was reduced to less than 10% of substrate conversion; however, all of the constructs were as stable as SacB. This shift in enzyme specificity was observed even when the SacB catalytic domain was extended only with the transitional region found in multidomain FSs. Specific kinetic analysis revealed that this change in specificity of the SacB chimeric constructs was derived from a 5-fold increase in the transfructosylation k(cat) and not from a reduction of the hydrolytic k(cat), which remained constant.

O-glycosylation expression in fibroadenoma.

Fibroadenomas are human benign breast tumors characterized by proliferation of epithelial and stroma cells of the terminal ductal unit. Expression of O-glycans seems to contribute to the proliferation and transformation events. With this in mind, we evaluated the expression of glycans in fibroadenoma tissue through immunohistochemistry with antibodies against mucin epitopes (Anti CA15-3 and MUC1), as well as with lectins specific for glycans linked to proteins or lipids, and we compared findings with healthy breast specimens. Our results show positive expression of CA15-3 and MUC1 in fibroadenoma tissue, mainly in duct and stroma cells, whereas, in normal samples, staining was observed in duct cells. The lectin from Glycine max recognized equally well duct and stroma cells; this was the only lectin showing co-localization with anti-CA15-3 in healthy and tumor tissues. Dolichos biflorus, Artocarpus integrifolia, and Griffonia simplicifolia lectins recognized duct cells in control healthy tissues as well as in fibroadenoma tissue. The lectin from Amaranthus leucocarpus recognized only duct cells in control samples, whereas, in fibroadenoma tissue, it recognized duct and some stromal cells, suggesting that O-glycans-type mucin linked to proteins and mucin participate in the development of fibroadenomas.