Biochemical characterization and immobilization of a PL25 family ulvan lyase for efficient degradation of Enteromorpha polysaccharide

Green algal polysaccharides such as ulvan and Enteromorpha polysaccharides (EPs) with versatile physiological activities have drawn increasing attentions as a renewable biomass resource. However, their activities and applications have been greatly limited by its high molecular weight and low solubility. Herein, a novel polysaccharide lyase (PL) family 25 ulvan lyase, termed EPD2, has been identified, heterologously expressed and biochemically characterized to efficient preparation of ulvan and Enteromorpha oligosaccharides. It consisted of 446 amino acids with a molecular weight of 50.28 kDa and shared the highest identity with the ulvan lyases of PL25 family. The EPD2 exhibited optimal activity (1764.95 U/mg and 179.9 U/mg for ulvan and EPs, respectively) at 50 °C. It also exhibited robust salt tolerance and could maintain high activity under high NaCl concentrations (0.4-1.2 M). The molecular docking results indicated that EPD2 produce oligosaccharides with degrees of polymerization (DPs) of 2-4 in an endolytic manner. To expand its applications, EPD2 was then immobilized onto sodium alginate and its structure was characterized. After immobilization, its stability at 40 °C was significantly enhanced. This research enriched the enzyme tools library for degrading Enteromorpha polysaccharide and facilitates the expanded application of these enzymes in preparation of oligosaccharides.