Elucidation of Domain Function of a Novel Multifunctional Glycoside Hydrolase and Its Use in Efficient Preparation of Oligosaccharides from Kelp Powder

Kelp contained laminarin, cellulose, and alginate as major polysaccharides and could be utilized as functional oligosaccharides. A new multifunctional glycoside hydrolase CelA was identified and characterized for the efficient degradation of kelp powder. It displayed cellulase (2308.38 U/mg), alginate lyase (578.68 U/mg), and laminarinase (720.97 U/mg) activities. It exhibited maximal activity on both sodium alginate and laminarin at 50 °C and pH 8.0, while it could degrade sodium carboxymethylcellulose (CMC-Na) by maximal activity at 40 °C and pH 7.0. The action mode analysis by thin layer chromatography and electrospray ionization mass spectrometry indicated that CelA adopted an endolytic manner to degrade CMC-Na, sodium alginate, and laminarin releasing oligosaccharides with degrees of polymerization (Dps) of 2–5. According to domain analysis, CelA contained a GH5 module and a PL6 module, and both of them exhibited glycoside hydrolase and polysaccharide lyase activity. The docking results revealed that Glu163 and Glu250 are essential in cellulose and laminarin degradation. As to the degradation of alginate, Asn376, Lys436, Arg464, Asp496, and Asn551 could bind alginate and Tyr492 and Lys529 acted as catalytic sites. CelA displayed high hydrolysis efficiency for cellulose, β-glucan, laminarin, alginate, and kelp powder. Thus, it has strong potential in food and feed industries as a catalyst for bioconversion of algal biomass into value-added products oligosaccharides.