Purification and characterization of an extracellular β-glucosidase from the filamentous fungus Acremonium persicinum and its probable role in β-glucan degradation

Abstract

A β-glucosidase from the culture filtrates of the filamentous fungus Acremonium persicinum has been purified by (NH 4) 2SO 4 precipitation followed by anion-exchange and gel filtration chromatography. SDS-PAGE of the purified enzyme gave a single band with an apparent molecular mass of 128 kDa. The enzyme is a monomeric protein with an isoelectric point of 4.3 and a pH optimum of 5.5. Comparison of the n-terminal amino acid sequence revealed similarities between the A. persicinum enzyme and several other extracellular fungal β-glucosidases including those from Trichoderma reesei, Aspergillus aculeatus, Saccharomycopsis fibuligera, and Pichia anomala. In addition to the hydrolysis of p-nitrophenyl-β-glucoside, the enzyme was also active against several other aryl-β-glucosides as well as a range of β-linked oligoglucosides including laminaribiose, gentiobiose, cellobiose, and sophorose. d-Glucono-1,5-lactone and glucose are competitive inhibitors while the enzyme was also inhibited by n-bromosuccinimide, n-acetylimidazole, dicyclohexyl carbodiimide, Woodward's Reagent K, 2-hydroxy-5-nitrobenzyl bromide, KMnO 4, and some metal ions. Possible roles for this enzyme in the noncellulolytic fungus A. persicinum are discussed in light of the increase in the rate of reducing sugar release from β-glucans by (1 → 3)- and (1 → 6)-β-glucanases when the β-glucosidase is also present in the reaction mixtures.