Dual α-1,4-and β-1,4-Glycosidase Activities by the Novel Carbohydrate-Binding Module in α-L-Fucosidase from Vibrio sp. Strain EJY3

Carbohydrates are structurally and functionally diverse materials including polysaccharides, and marine organisms are known to have many enzymes for the breakdown of complex polysaccharides. Here, we identified an alpha-L-fucosidase enzyme from the marine bacterium Vibrio sp. strain EJY3 (VejFCD) that has dual alpha-1,4-glucosidic and beta-1,4-galactosidic specificities. We determined the crystal structure of VejFCD and provided the structural basis underlying the dual alpha- and beta-glycosidase activities of the enzyme. Unlike other three-domain FCDs, in VejFCD, carbohydrate-binding module-B (CBM-B) with a novel beta-sandwich fold tightly contacts with the CatD/CBM-B main body and provides key residues for the beta-1,4-glycosidase activity of the enzyme. The phylogenetic tree analysis suggests that only a few FCDs from marine microorganisms have the key structural features for dual alpha-1,4-and beta-1,4-glycosidase activities. This study provides the structural insights into the mechanism underlying the novel glycoside hydrolase activities and could be applied for more efficient utilization in the hydrolysis of complex carbohydrates in biotechnological applications.