Biochemical characterization and elucidation the action mode of a new PL25 family ulvan lyase from marine bacterium Alteromonas sp. TK-45 (2)

Ulvan, extracted from the marine green algae belonging to the genus Ulva, is a complex water-soluble sulfated polysaccharide which mainly composed of four monosaccharides consisting of rhamnose, xylose, glucuronic acid and iduronic acid. Its complex monosaccharide composition gives ulvan great potential for application in the fields of food, pharmaceuticals, and chemistry. And it can be degraded by ulvan lyases mainly from Polysaccharide Lyases (PL) family of PL24, PL25 and PL28 through β-elimination mechanism, which cleaves the β-glycosidic bond between sulfated rhamnose and glucuronic acid or iduronic acid, thereby producing an Ulva oligosaccharide with unsaturated bond. In this study, we have identified a putative ulvan lyase from Alteromonas sp. TK-45 (2). We heterologously expressed, purified, and biochemically characterized the ulvan lyase, which has removed signal peptide. The results show that ULA-1 had best activity at 45 °C and pH 8.0. The K_m and V_max values were 13.25 μg·mL⁻¹ and 1.719 μmol·min⁻¹·mL⁻¹, respectively. The thermostability of ULA-1 was excellent, and its activity hardly decreased after incubation at 45 °C for 1 h. ESI-MS analysis showed that the primary end-product were disaccharides to tetrasaccharides. In conclusion, our research has expanded the database of ulvan lyase, and provided the possibility to make full use of ulvan, a huge marine biomass resource.