Catalytic function of a newly purified exo-β-D-glucosaminidase from the entomopathogenic fungus Paecilomyces lilacinus

Abstract

An entomopathogenic fungus, Paecilomyces lilacinus, was found to grow on chitosanase-detecting plates. Besides an endo-chitosanase, an exo-β-D-glucosaminidase was purified by cation-exchange chromatography from this microorganism cultivated in M9 minimal media containing 0.5% chitosan as the sole carbon source. The molecular weight of the enzyme is 95kDa; the optimum pH and temperature for activity are 6.0 and 45°C, respectively. The purified exo-β-D-GlcNase promotes the hydrolysis of 95% deacetylated chitosan from its non-reducing end and liberates 2-amino-2-deoxy-D-glucopyranose (GlcN) as the sole product; however, 2-acetamido-2-deoxy-D-glucopyranose (GlcNAc) was not detected when chitin was used as the substrate. The cleavage pattern confirmed using real-time mass spectrometry shows that exo-β-D-glucosaminidase cleaves the glycosidic bonds between GlcN-GlcN and GlcN-GlcNAc but not between GlcNAc-GlcN or GlcNAc-GlcNAc. In the presence of a 10% solution of various alcohols, many alkyl-β-D-glucosaminides were obtained, indicating that exo-β-D-glucosaminidase is a retaining enzyme.