Biochemical characterization of a novel bifunctional cellulase-glucanase and its application for efficient degradation of kelp powder.

Cellulases and glucanases can effectively degrade the seaweed polysaccharides, and the resulting oligosaccharides may be subsequently fermented or used as feed additives. To improve the utilization of marine algae, the study identified and characterized Cel5B, a novel bifunctional cellulase-glucanase from Cellulophaga lytica. Phylogenetic tree analysis indicated that Cel5B belongs to the GH5_2 subfamily. It exhibited high degrading activities towards β-1, 3-glucan (7527.13 U/mg), CMC-Na (3390.93 U/mg) and lichenan (4343.32 U/mg). The optimal temperatures for Cel5B were determined to be 50 °C and 40 °C, respectively, when β-1,3-glucan and CMC-Na were used as substrates, with an optimum pH of 6.0. The action mode and product analysis by TLC, HPLC and ESI-MS indicated Cel5B adopted an endolytic manner to degrade the β-1, 3-glucan, CMC-Na and lichenan releasing oligosaccharides with degrees of polymerization (DP) of 1-6, 1-4 and 1-4 as the main component, respectively. This suggests that Cel5B can degrade both β-1, 3-glycosidic bonds and β-1, 4-glycosidic bonds. Homology modeling and molecular docking showed that Cel5B shared the typical (β/α)-barrel structure of the GH5 family with catalytic residues Glu191 and Glu279. Cel5B was added to the kelp powder solution that had been degraded by alginate lyase, and the total amount of reducing sugar was increased by 21.97 % after the reaction for 3 h. This proved that Cel5B could indeed improve the utilization of seaweeds, and it is expected to be a tool enzyme for the high-value utilization of seaweeds.