Biochemical and milk-clotting properties and mapping of catalytic subsites of an extracellular aspartic peptidase from basidiomycete fungus Phanerochaete chrysosporium

Abstract

For a long time, proteolytic enzymes have been employed as key tools of industrial processes, especially in the dairy industry. In the present work, we used Phanerochaete chrysosporium for biochemical characterization and analysis of catalytic specificity of an aspartic peptidase. Our results revealed an aspartic peptidase with molecular mass ∼38kDa, maximal activity at pH 4.5 and 50°C, and stability above 80% in the pH range of 3-8 and temperature up to 55°C for 1h. In a milk-clotting assay, this peptidase showed maximal milk clotting activity at 60-65°C and maintenance of enzymatic activity above 80% in the presence of 20mM CaCl₂. In a specificity assay, we observed stronger restriction of catalysis at the S₁ subsite, with a preference for lysine, arginine, leucine, tyrosine, and phenylalanine residues. The restricted proteolysis and milk-clotting potential are attractive properties for the use in cheese production.

Keywords: Aspartic protease; FRET; Fungal enzyme; Milk-clotting; Phanerochaete chrysosporium.