Acasp, a gene encoding a cathepsin D-like aspartic protease from the hookworm Ancylostoma caninum

Intestinal infection with the zoonotic hookworm Ancylostoma caninum can provoke human eosinophilic enteritis. A cDNA was isolated from A. caninum, using an oligonucleotide primer designed to hybridize to the region encoding the consensus, catalytic site residues D32TGSSNLW of aspartic proteases. This novel cDNA encoded an aspartic protease zymogen of 422 amino acids, exhibiting 47% identity to the lysosomal aspartic protease of Aedes aegypti, 46% identity to the aspartic protease of Schistosoma japonicum, and 48.5% to human cathepsin D. Its deduced structure differed from that of cathepsin D in the loop 2 "flap," which holds the substrate at the active site, and by the presence of a COOH-terminal extension of approximately 30 residues.