Characterization of a β-N-acetylhexosaminidase CgNagase20 from Chaetomium globosum with antifungal activity against Fusarium sporotrichioides.

Abstract

Chitinolytic enzymes are capable of hydrolyzing the cell walls of pathogenic fungi, disrupting the exoskeletons of insect pests, and producing N-acetyl-β-D-glucosamine oligomers or monomers. In this study, a new β-N-acetylhexosaminidase gene encoding an enzyme from glycoside hydrolase family 20 (GH 20) was identified from the biocontrol fungus Chaetomium globosum W7. The corresponding protein was designated CgNagase20 and was heterologously expressed in Escherichia coli. The molecular mass of the protein was approximately 66.7 kDa, and this enzyme exhibited maximal activity at 55 °C and pH 4.0. Heavy metal ions, particularly Fe³⁺, Ag⁺, and Hg²⁺, were found to strongly inhibit CgNagase20 activity. CgNagase20 exhibits typical substrate specificity of β-N-acetylhexosaminidase (EC 3.2.1.52), acting on N-acetylglucosides and N-acetylgalactosides, with monosaccharides as the sole end products. The Vmax and Km values for CgNagase20 when acting on 4-nitrophenyl N-acetyl-β-D-glucosaminide (pNP-βGlcNAc) were calculated to be 118.85 µmol/min/mg protein and 1.59 mM, respectively. Additionally, CgNagase20 demonstrated antifungal activity, significantly inhibiting spore germination and hyphal growth of Fusarium sporotrichioides, the causative agent of potato dry rot. In conclusion, CgNagase20 represents the first β-N-acetylhexosaminidase identified and characterized from C. globosum, with potential applications in both the industrial and agricultural sectors.