Sp22D: a multidomain serine protease with a putative role in insect immunity

Serine proteases play critical roles in a variety of insect immune response s: however, few of the genes that code for these enzymes have been cloned. Here, we describe the molecular characterization of a serine protease gene from the mosquito Anopheles gambiae. Sp22D codes for a 1322 amino acid poly peptide with a complex domain organization. In addition to the carboxy term inal serine protease catalytic domain, Sp22D contains two putative chitin b inding domains, a mucin-like domain, two low density lipoprotein receptor c lass A domains, and two scavenger receptor cysteine rich domains. A typical signal peptide sequence and a lack of potential transmembrane helices sugg est that Sp22D is secreted. Sp22D is expressed constitutively in three immu ne-related cell types: adult hemocytes, fat body cells, and midgut epitheli al cells. Wounding induces no changes in transcript abundance, but within 1 h after injection of bacteria, Sp22D mRNA increases 1.5-fold. Based on dom ain organization, tissue distribution, and transcriptional up-regulation in response to immune challenge, we suggest that Sp22D has an immune function . In addition, we predict that Sp22D is secreted into the hemolymph where i t may interact with pathogen surfaces and initiate an immune response, (C) 2000 Published by Elsevier Science B.V. All rights reserved.