The first characterized asparaginase from a basidiomycete, Flammulina velutipes

Abstract

Flammulina velutipes enjoys high popularity as an edible mushroom in Asian cuisines. Investigating the secretion of peptidases in nutrient media enriched with gluten, an enzyme was noticed that catalyzed the deamidation of L-asparagine and L-glutamine. The enzyme was purified to electrophoretic homogeneity by foaming and SEC. PAGE analysis revealed a protein of about 85 kDa with 13 kDa subunits indicating a hexameric protein. Degenerated primers were deduced from peptide fragments and the complete coding sequence of 372 bp was determined. The gene of Flammulina velutipes asparaginase (FvNase) over expressed in E. coli achieved an L-asparagine-hydrolyzing activity of 16 U/mL in crude extract, which was five times higher than its L-glutamine-hydrolyzing ability. The enzyme showed a pH-optimum at pH 7, remarkable tolerance towards elevated temperature and sodium chloride concentration in both the native and recombinant form, and no significant homology to any conserved domains of published asparaginases or glutaminases.