Serpins from an Insect, Manduca sexta

Abstract

Members of the serpin superfamily have been identified in several invertebrate species, primarily as proteins in the hemolymph of animals from the phylum Arthropoda⁹. Serpin cDNAs have been cloned from horseshoe crabs^14,15, a crayfish¹³, two species of lepidopteran insects^{6,10,17,20,24}, the fruit fly Drosophila melanogaster ³, trematodes from the genus Schistosoma ², and from a parasitic nematode²⁵. The presence of serpins with differing proteinase inhibitory activities in the hemolymph of horseshoe crabs and insects suggests that serpins may function in several physiological processes in invertebrates, as they do in mammals. The number of invertebrate species vastly exceeds the number of vertebrates, with far greater biological diversity. Thus, it may be predicted that as biochemical studies on invertebrates progress, a large number of serpins with diverse activities and functions will be discovered. In our research on serpins from the tobacco hornworm, Manduca sexta, we have identified a family of serpins with different inhibitory activities, and a unique serpin gene structure for generating reactive site diversity.