Comparative characterization of laminarinases from the filamentous marine fungi Chaetomium indicum Corda and Trichoderma aureviride Rifai

Abstract

Marine filamentous fungi (103 strains) isolated from various marine habitats were studied for their ability to produce extracellular O-glycosylhydrolases. Cultural filtrates of these strains were shown to contain a series of glycanases (laminarinases, amylases, cellulases, pustulanases) and glycosidases (β-glucosidases, N-acetyl-β-glucosaminidases, β-galactosidases, α-mannosidases). Two species of marine fungi from different habitats were chosen for isolation of laminarinases and detailed study on enzyme properties. The fungus Chaetomium indicum associated with the alga Fucus evanescens C. Agardh was collected near the Kuril Islands, and Trichoderma aureviride was sampled from bottom deposits of South China Sea. Properties of extracellular laminarinases were similar: temperature optimums (40–45 °C), molecular masses (54–56 kDa), K_m (0.1–0.3 mg mL⁻¹). Temperature stability of laminarinase of C. indicum was significantly higher than those from Trichoderma aureveride. It is shown that these enzymes are specific to β-1,3-bonds in glucans, release predominantly glucose from laminaran and do not catalyze reaction of transglycosylation. Accoding to these data enzymes are exo-1,3-β-D-glucan-glucanohydrolases (EC 3.2.1.58). Inhibitor analysis demonstrated the significant role of tryptophan and tyrosine residues in the catalytic activity of enzymes. Molecules of T. aureviride laminarinase contained the functionally important thiol group.