Characterization of a novel PL 17 family alginate lyase with exolytic and endolytic cleavage activity from marine bacterium Microbulbifer sp. SH-1.

Alginate lyases are essential tools for depolymerizing alginate into bioactive oligosaccharides and fermentable monosaccharides. Herein, we characterized a novel polysaccharide lyase AlgSH17 from marine bacterium Microbulbifer sp. SH-1. The recombinant enzyme exhibited the maximum activity at 30 °C, pH 7.0 and retained 86.20% and 65.43% of its maximum activity at 20 °C and 15 °C, respectively, indicating that AlgSH17 has an excellent cold-adapted property. The final products of AlgSH17 mainly consisted of monosaccharides with small amounts of oligosaccharides with degrees of polymerization (DP) 2-6, suggesting that AlgSH17 possesses both exolytic and endolytic activity. Degradation pattern analysis indicated that AlgSH17 could degrade DP ≥ 4 oligosaccharides into disaccharides and trisaccharides by cleaving the endo-glycosidic bonds and further digest disaccharides and trisaccharides into monosaccharides in an exolytic manner. Products distribution and molecular docking analysis revealed that AlgSH17 could cleave the glycosidic bonds between -1 and +2 within the substrate. Furthermore, The ABTS+, hydroxyl and DPPH radicals scavenging activity of the enzymatic hydrolysates prepared by AlgSH17 reached up to 91.53%, 81.23% and 61.06%, respectively, and the enzymatic hydrolysates displayed an excellent preservation effect on fresh-cut apples. The above results suggested that AlgSH17 could be utilized for the production of monosaccharides, antioxidants and food additives.