Characterization of a thermostable endo-1,3(4)-β-glucanase from Caldicellulosiruptor sp. strain F32 and its application for yeast lysis.

β-1,3-Glucans, important structural components of cell wall or nutritional components of the endosperm, are extensively found in bacteria, fungi, yeast, algae, and plants. The structural complexity of β-1,3-glucans implies that the enzymatic depolymerization of polysaccharides needs combined activities of distinct enzymes. In this study, Lam16A-GH, the catalytic module of a putative glycoside hydrolase (GH) family 16 laminarinase/lichenase from thermophilic bacterium Caldicellulosiruptor sp. F32, was purified and characterized through heterologous expression in Escherichia coli. Lam16A-GH can hydrolyze both β-1,3-glucan (laminarin) and β-1,3-1,4-glucan (barley β-glucan) revealed by analysis of the products of polysaccharide degradation using thin-layer chromatography (TLC). The time required for the loss of 50 % of its activity is 45 h under the optimal condition of 75 °C and pH 6.5. Oligosaccharides degradation assay indicated that Lam16A-GH can catalyze endo-hydrolysis of the β-1,4 glycosidic linkage adjacent to a 3-O-substituted glucosyl residue in the mixed linked β-glucans, as well as the β-1,3 linkage. The survival rate of Saccharomyces cerevisiae cells depends on the addition of Lam16A-GH, and the cytoplasm protein was released from the apparently deconstructed yeast cells. These results indicate that the bi-functional thermostable Lam16A-GH exhibits unique enzymatic properties and potential for yeast lysis.