Heterologous expression and biochemical characterization of acetyl xylan esterase from Coprinopsis cinerea

Acetyl xylan esterase (AXE) from basidiomycete Coprinopsis cinerea Okayama 7 (#130) was functionally expressed in Pichia pastoris with a C-terminal tag under the alcohol oxidase 1 (AOX1) promoter and secreted into the medium at 1.5 mg l(-1). Its molecular mass was estimated to be 65.5 kDa based on the SDS-PAGE analysis, which is higher than the calculated molecular mass of 40 kDa based on amino acid composition. In-silico analysis of the amino acid sequence predicted two potential N-glycosylation sites. Results from PNGase F deglycosylation and mass spectrum confirmed the presence of N-glycosylation on the recombinant AXE with predominant N-glycans HexNAc2Hex9-16. The recombinant AXE showed best activity at 40 °C and pH 8. It showed not only acetyl esterase activity with a Km of 4.3 mM and a Vmax of 2.15 U mg(-1) for hydrolysis of 4-nitrophenyl acetate but also a butyl esterase activity for hydrolysis of 4-nitrophenyl butyrate with a Km of 0.11 mM and Vmax of 0.78 U mg(-1). The presence of two additional amino acid residues at its native N-terminus was found to help stabilize the enzyme against the protease cleavages without affecting its activity.