Heterologous expression and characterisation of the Aspergillus aspartic protease involved in the hydrolysis and decolorisation of red‐pigmented proteins

BACKGROUND Aspergillus repens strain MK82 produces an aspartic protease (PepA_MK82) that efficiently decolorises red‐pigmented proteins during dried bonito fermentation. However, further expansion of the industrial applications of PepA_MK82 requires the high‐level production and efficient preparation of the recombinant enzyme. RESULTS The genomic DNA and cDNA fragments encoding the protease were cloned from strain MK82 and sequenced. Phylogenetic analysis of PepA_MK82 and comparisons with previously reported fungal aspartic proteases showed that PepA_MK 82 clusters with different groups of these enzymes. Heterologous expression of PepA_MK82 in Pichia pastoris yielded preparations of higher purity than obtained with an Escherichia coli expression system. Total protease activity in a 100‐mL culture of the P. pastoris transformant was 14 times higher than that from an equivalent culture of A. repense MK82. The recombinant PepA_MK82 was easily obtained via acetone precipitation; the final recovery was 83%. PepA_MK82 and its recombinant had similar characteristics in terms of their optimal pH, thermostability, and decolorisation activity. The recombinant was also able to decolorise flaked, dried bonito and to bleach a blood‐stained cloth. CONCLUSION Given its ability to hydrolyse and decolorise red‐pigmented proteins, recombinant PepA_MK8 can be exploited in the food industry and as a stain‐removal agent in laundry applications. © 2016 Society of Chemical Industry