A Novel Thermostable Laminarinase with High Activity from Streptomyces albus and Its Catalytic Characteristics in Laminarin Degradation

Laminarin oligosaccharides (LOSs) degraded from laminarin present nutritional functions. Laminarinases with high activity and good stability are significant tools for LOS production. OUC-SaLam66, a novel GH128 laminarinase from Streptomyces albus, was heterologously expressed. OUC-SaLam66 harbored a significant activity advantage up to 2294.80 U/mg at 45 °C and pH 4.0; meanwhile, it could preserve 80% activity at 45 °C for 12 h, indicating good stability. Significantly, its residual activity was over 75% after incubating at 100 °C for 1 h. Differential scanning calorimetry and molecular dynamic modeling revealed that its melting point and RMSD average point were 114.83 °C and 0.125 nm at 100 °C, respectively, which further proved its superior stability. Its apparent Km and Vmax against laminarin were 6.437 mM and 2.5 μg/min/mg, respectively. Hydrolysis products were mainly composed of laminaritriose and laminaribiose. The high activity and thermostability of OUC-SaLam66 make it a promising candidate for LOS preparation.