Characterization of an Endo-1,3-fucanase from Glycoside Hydrolase Family 187 Within a Polysaccharide Utilization Locus of Wenyingzhuangia aestuarii OF219

Sulfated fucan is a bioactive component prevalent in brown algae and echinoderms. Endo-1,3-fucanase plays a pivotal role in the structure analysis and oligosaccharide preparation of sulfated fucans. However, the action mode and molecular mechanism of endo-1,3-fucanase remain largely unexplored. This study identified a new endo-1,3-fucanase Fun187B within the GH187 family, which exhibits only a 26.2% sequence identity to the sole characterized member of the family (Fun187A). Fun187B could cleave sulfated fucan from Thelenota ananas in an endoacting mode and produced the trisaccharide α-l-Fucp2(OSO₃^-)-1→3-α-l-Fucp-1→3-α-l-Fucp2(OSO₃^-) as the major product, which is distinct from Fun187A. Structure prediction by Alphafold3 combined with molecular docking showed that Fun187B recognized the substrate through a series of polar amino acids. The structural analogues of Fun187B are widely distributed among polysaccharide-degrading specialized bacteria. This study provides novel perspectives on the GH187 endo-1,3-fucanase, introducing a favorable tool for enhancing investigations and applications associated with sulfated fucans.