Efficient Expression of an Alginate Lyase from Vibrio alginolyticus and Its Application in the Preparation of Guluronate Oligosaccharides

In this study, a novel alginate lyase-encoding gene, VaAly7, was identified from Vibrio alginolyticus and efficiently expressed in Pichia pastoris, with an enzyme activity of 413 U/mL. The recombinant enzyme (VaAly7) was purified to electrophoretic homogeneity using QSFF strong anion exchange column chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the molecular mass of the purified enzyme was approximately 44 kDa. The optimal temperature and pH of the enzyme were 30 ℃ and 7.0, respectively. This enzyme was activated by salts, and its activity was increased by about eight folds in the presence of 400 mmol/L NaCl. VaAly7 was a bifunctional alginate lyase with a preference for poly-guluronic acid and the shortest chain substrate that could be degraded by it was pentasaccharide. VaAly7 was used to degrade 10% polyguluronic acid solution, producing guluronate oligosaccharides (AOSs) with a yield of 86%. The degrees of polymerization of the products were in the range of 1–5 with an average molecular mass of 2.1 kDa. The enzyme shows potential in the preparation of guluronate oligosaccharides.