Construction and characterization of a novel fusion alginate lyase with endolytic and exolytic cleavage activity for industrial preparation of alginate oligosaccharides

Alginate lyases with high activity and good thermostability are lacking for the preparation of alginate oligosaccharides (AOS) with various biological activities. We constructed a fusion alginate lyase with both endo -and exo -activities. Aly Rm 6A- Zu 7 was successfully constructed by connecting the highly thermostable Aly Rm 6A to a new exotype lyase, Aly Zu 7. The fusion enzyme exhibited high catalytic activity and thermostability. It transformed sodium alginate into oligosaccharides with degrees of polymerization (DP) of 2 -4 while producing 4deoxy-L- erythro -5-hexoseulose uronic acid (DEH). The maximum reducing sugar, AOS, and DP1 + DEH yields were 75 %, 45 %, and 40 %, respectively. Molecular docking confirmed the formation of a stable complex between the substrate and Aly Rm 6A- Zu 7. Protein interactions increased the thermostability of Aly Zu 7. This work provides new insights into the industrial formation of AOS and monosaccharide DEH using thermally stable fusion enzymes, which has a positive effect in the fields of functional oligosaccharide production and biofuel formation.