Discovery of a sulfated fucan-specific carbohydrate-binding module: The first member of a new carbohydrate-binding module family

Sulfated fucan is an important functional polysaccharide with various physiological activities. Carbohydrate-binding module (CBM) is a representative class of carbohydrate-binding protein, which could be employed as a favorable tool for the investigations and applications of polysaccharides. Nevertheless, only one confirmed sulfated fucan-binding CBM has been hitherto reported. In the present study, an unknown domain with a predicted β-sandwich fold was discovered from a fucanase Fun174A, and further cloned and heterologously expressed in Escherichia coli. The expressed protein Fun174A-CBM displayed a specific binding capacity to sulfated fucan. The bio-layer interferometry assays showed that the protein could bind to the sulfated fucan tetrasaccharide with an affinity constant of 2.83 × 10−4 M. Fun174A-CBM shared no significant sequence similarity to any identified CBMs, indicating that it represents a new CBM family. The discovery of Fun174-CBM and the novel CBM family would be beneficial to the investigations of sulfated fucan-binding proteins.