Sequence Engineering of an Aspergillus niger Tannase to Produce in Pichia pastoris a Single-Chain Enzyme with High Specific Activity

Abstract

Tannin acyl hydrolases or tannases (E.C.3.1.1.20) are enzymes that hydrolyze the ester bond of tannins to produce gallic acid and glucose. We engineered the Aspergillus niger GH1 tannase sequence and Pichia pastoris strains to produce and secrete the enzyme as a single-chain protein. The recombinant tannase was N-glycosylated, had a molecular mass after N-deglycosylation of 65.4kDa, and showed activity over broad pH and temperature ranges, with optimum pH and temperature of 5.0 and 20°C. Furthermore, the single-chain tannase had an 11-fold increased specific activity in comparison to the double-chain A. niger GH1 tannase, which was also produced in P. pastoris. Structural analysis suggested that the high specific activity may be due to the presence of a flexible loop in the lid domain, which can control and drive the substrate to the active site. In contrast, the low specific activity of the double-chain tannase may be due to the presence of a disordered and flexible loop that could hinder the substrate's access to the binding site. Based on its biochemical properties, high specific activity, and the possibility of its production in P. pastoris, the tannase described could be used in food and beverage processing at low and medium temperatures.