Study of protease activity from Aspergillus awamori INCQS2B.361U2/1 extracellular fraction and modification of culture medium composition to isolate a novel aspartic protease.

Abstract

Aspergillus awamori was cultivated in a modified Breccia medium, and the extracellular fraction was obtained, which presented 260 ± 15µg of protein/mg and specific protease activity of 3.87 ± 0.52mM.min-1.mg of protein-1 using Nα-p-tosyl-L-arginine methyl ester hydrochloride (L-TAME) as substrate. This fraction showed major proteins about 104 and 44kDa and maximal protease activity at pH 5.5, 6.5, and 9.0, suggesting that A. awamori secretes acidic, neutral, and alkaline proteases with expressive thermal stability, however, aspartic protease was the most important activity. When yeast extract was supplemented to a modified Breccia medium, A. awamori protein secretion and protease activity were maximal and the affinity chromatography on pepstatin-agarose was employed to isolate the aspartic protease activity, which was called ASPA, with approximately 75kDa. ASPA maximal activity was obtained at pH 4.5 and 6.5, and 50°C. Pepstatin inhibited about 80% of ASPA activity, with IC50 and Ki values of 0.154 and 0.072μM, respectively. ASPA cleaved protein and peptides substrates with the highest activity against gelatin (95 U/mg) and good peptidase activity with KM 0.0589mM and Vmax 1.909mM.min-1.mg protein-1, using L-TAME as substrate. A. awamori extracellular fraction is a source of proteases with important activity, and the supplementation of modified Breccia medium increased the aspartic protease production. This enzyme presented different biochemical characteristics from the previously reported A. awamori aspartic proteases. Therefore, ASPA is an excellent candidate for biotechnological application due to its important activity and thermostability.