Expression, Purification, and Characterization of the Recombinant Pepsin Inhibitor from Ascaris suum

Abstract

Only a few natural inhibitors of aspartic proteinases have been discovered to date. A small number of peptides from bacterial origins have been shown to inhibit members of this protease family.^1-2 Larger proteinaceous inhibitors of aspartic proteases have been discovered in the potato³ (cathepsin D inhibitor), in yeast,⁴ and the intestinal nematode Ascaris.^5–7 Similar genes have been discovered in other parasitic nematodes.⁸ The Ascaris aspartic proteinase inhibitor (PI-3) is a 16.7 kDa protein that specifically inhibits pepsin, gastricsin, and, less strongly, cathepsin E. This inhibitor possesses six cysteine residues which form three disulfide bridges, and it contains helical and strand structural motifs.