Serine Protease Inhibitors from the Serpin Gene Family in Manduca sexta and Drosophila melanogaster

Abstract

The hemolymph of lepidopteran insects has been shown to contain two classes of proteins that inhibit serine proteases (reviewed in Kanost et al., 1990). Low molecular weight proteins (7–9 kDa) from both Bombyx mori (Sasaki, 1984) and Manduca sexta (Ramesh et al., 1988) have been shown to be homologous with the vertebrate Kunitz-type inhibitors such as pancreatic trypsin inhibitor. A group of larger proteins (42–47 kDa) are members of the serpin family of serine protease inhibitors (Kanost et al., 1989). The serpins include mammalian serum proteins such as α1-antitrypsin, antithrombin, β2-antiplasmin, and plasminogen activator inhibitor (Boswell and Carrell, 1988). A trypsin inhibitor (42 kDa) and a chymotrypsin inhibitor (43 kDa) from hemolymph of B. mori larvae (Sasaki and Kobayashi, 1984; Eguchi and Shomoto, 1985) have properties similar to the vertebrate serpins, including a mechanism in which the enzyme and inhibitor form a stable complex after cleavage of a reactive site near the inhibitor’s COOH-terminal (Sasaki, 1985; Sasaki et al., 1987).