Production, purification, and characterization of an extracellular endo-β-1, 3-glucanase from a monokaryon of Schizophyllum commune ATCC 38548 defective in exo-β-1, 3-glucanase formation

Production of extracellular β-1, 3-glucanase activity by a monokaryotic Schizophyllum commune strain was monitored and results indicated that the β-glucanase activity consisted of an endo- β-1, 3-glucanase activity, besides a negligible amount of β-1, 6-glucanase and β-glucosidase activity. Unlike the β-1, 3-glucanase production of the dikaryotic parent strain S. commune ATCC 38548, the β-1, 3-glucanase formation of the monokaryon was not regulated by catabolite repression. The endo- β-1, 3-glucanase of the monokaryon was purified from the culture filtrate by lyophilization, anion exchange chromatography on Mono Q, and gel filtration on Sephacryl S-100. It appeared homogeneous on SDS-PAGE with a molecular mass of 35.5 kDa and the isoelectric point was 3.95. The enzyme was only active toward glucans containing β-1, 3-linkages, including lichenan, a β-1, 3-1, 4-D-glucan. It attacked laminarin in an endo-like fashion to form laminaribiose, laminaritriose, and high oligosaccharides. While the extracellular β-glucanases from the dikaryotic S. commune ATCC 38548 degraded significant amounts of schizophyllan, the endo- β-1, 3-glucanase from the monokaryon showed greatly reduced activity toward this high molecular mass β-1, 3-/β-1, 6-glucan. The Km of the endoglucanase, using laminarin as substrate, was 0.28 mg/mL. Optimal pH and temperature were 5.5 and 50 °C, respectively. The enzyme was stable between pH 5.5 and 7.0 and at temperatures below 50 °C. The enzyme was completely inhibited by 1 mM Hg2+. Growth of the monokaryotic S. commune strain was not affected by its constitutive endo- β-1, 3-glucanase formation.Key words: endo- β-1, 3-glucanase, Schizophyllum commune, monokaryon, constitutive endo- β-1, 3-glucanase formation.