Cystatin-like domain of mouse countertrypin, a member of mammalian fetuin family, is responsible for the inhibition of trypsin. Evidence from site-directed mutagenesis.

Abstract

Members of mammalian fetuin family, such as human alpha 2 HS glycoprotein and bovine fetuin, consist of three domains, two tandemly arranged cystatin-like domains and an unrelated domain, but they have no inhibitory activity against cysteine proteinases. We found that countertrypin, a novel trypsin inhibitor, is mouse counterpart of human alpha 2 HS glycoprotein, and that human alpha 2 HS glycoprotein and bovine fetuin which were prepared without use of ethanol are capable of inhibiting trypsin (Yamamoto, K. and Sinohara, H. (1993) J. Biol. Chem, 268, 17750-17753). In the present study, cDNA encoding countertrypin was isolated and sequenced, and evidence is presented, based on the site-directed mutagenesis, that lysine-231 in the second cystatin domain is the P1 site for trypsin inhibition.