Expression and characterization of a novel lipase from Aspergillus fumigatus with high specific activity

A novel lipase gene from Aspergillus fumigatus, afl1-1, was cloned and expressed with a molecular mass of 38 kDa in Escherichia coli for the first time. The recombinant lipase had a preference for short carbon chain p-nitrophenyl esters, especially toward C2 p-nitrophenyl ester and exhibited potent hydrolysis activity that had not been observed. The optimum pH and temperature of this new enzyme were 8.5 and 65 °C, respectively. The recombinant lipase (AFL1-1) is an alkaline enzyme which was stable in the pH range 6.0∼8.5 for 16 h (at 4 °C) and at 30∼50 °C for 1 h. It is an intracellular enzyme which was purified approximately 8.47-fold with an overall yield of 86.1% by single-step Ni-NTA affinity purification, with a very high specific activity of approximately 1.00 × 10(3) U mg(-1) on a standard substrate of p-nitrophenyl acetate. The Michaelis-Menten kinetic parameters V (max) and K (m) of the lipase were 1.37 mM mg(-1) min(-1) and 14.0 mM, respectively. Ca(2+) and other metal ions could not activate the lipase. According to the homology analysis and site-directed mutagenesis assay, the catalytic triad of the recombinant lipase was identified as Ser-165, Asp-260, and His-290 residues.