Leuconostoc citreum SK24.002 glucansucrase: Biochemical characterisation and de novo synthesis of α-glucan

• A cell-associated glucansucrase was obtained from Leuconostoc citreum SK24.002.
• The glucansucrase was purified and biochemically characterized.
• Glucansucrase was used for de novo synthesis of α-glucan and acceptor-products.
• NMR spectroscopy showed α-glucan having 58% α-1,6 linkages and 42% α-1,3 bonds.
• LC–MS/MS analysis revealed structure of maltose acceptor products including trisaccharide, tetrasaccharide and pentasaccharide.

The cell-associated glucansucrase from Leuconostoc citreum SK24.002 was isolated, purified, characterized and used for de novo synthesis of α-glucan and acceptor-products. The final specific glucansucrase activity was 1.4 U/mg protein with 13.2-fold purification. The obtained glucansucrase had a molecular weight of 186 kDa, Tm of 61.7 °C and △H of 176.7 kJ/mol. The enzyme showed maximum activity at pH 5.0-6.0 and 45 °C. The enzyme activity was enhanced by Ca2+, Mn2+ or Co2+ ions, whereas the activity decreased as the methanol, ethanol, n-butanol, DMSO or isopropanol concentration increased. The chemical inhibitors including BD, DTNB, EDC or NBS also significantly inhibited enzyme activity. Km, Vmax and kcat of glucansucrase were 10.9 mM, 3.6 U/mg and 306.6 1/s, respectively. For de novo synthesis from sucrose, α-glucan polymer with molecular weight of 1.5 × 107 g/mol and maltose acceptor products (trisaccharide, tetrasaccharide and pentasaccharide) were obtained by glucansucrase via glucosyltransfer reactions, respectively.