Biochemical characterization of a novel bifunctional alginate lyase from Microbulbifer arenaceous

Bio‒production of alginate oligosaccharides (AOSs), a type of functional food additive, is a promising way for green utilization of algae, in which alginate hydrolyzing enzymes play a key role. A novel alginate lyase gene (MiAly17A) from a marine bacterium Microbulbifer arenaceous was heterologously expressed in E. coli. The coding sequence of the gene shared the highest identity of 86% with a polysaccharide lyase (PL) family 17 alginate lyase (AlgL17) from Microbulbifer sp. ALW1. The recombinant enzyme (MiAly17A) was purified and biochemically characterized. MiAly17A showed maximal enzyme activity at 40 °C and pH 7.5, respectively. It was stable at the temperatures below 35 °C and within pH 5.0-8.0. The enzyme activities were increased by 5.3 and 5.6 folds in the presence of 100 mM of K⁺ and Na⁺, respectively. MiAly17A was bifunctional and could hydrolyze sodium alginate to release unsaturated monosaccharides and oligosaccharides with degrees of polymerization (DP) 2-7. The enzyme catalyzed the cleavage of glycosidic bonds from the non-reducing ends and the backbone of the tested oligosaccharides (DP ≥ 4), exhibiting both exolytic and endo-lytic activities. Moreover, MiAly17A was used for the production of alginate oligosaccharides from sodium alginate, and the highest conversion ratio of 68% was obtained. The unique properties may possess the enzyme great potential for preparation of alginate oligosaccharides.