Cloning and characterization of midgut-specific gene/gene products in the mosquito Aedes aegypti

Abstract

The yellow fever and dengue fever carrying mosquito, Aedes aegypti, requires blood feeding for egg production. The blood proteins are digested in the midgut to yield amino acids which are the nutritional source for oogenesis. Serine proteases are important enzymes that participate in the process of blood protein digestion. The identification of the corresponding genes may have significant implications in the control of mosquito-borne diseases. A gut-specific chymotrypsin-like cDNA was isolated and sequenced. The 938 bp clone encodes a preproenzyme with a putative 18 amino acid signal peptide sequence, a 7 amino acid activation peptide sequence rich in serine and charged residues, and a mature enzyme of 268 amino acids. The deduced amino acid sequence has a typical catalytic triad region for serine proteases (His 57, Asp 102 and Ser 195 in bovine chymotrypsin numbering system), and the hydrophobic substrate binding pocket with most features of chymotrypsins. Six cysteine residues are present in the sequence which are characteristically involved in disulfide bond formation in invertebrate serine proteases. Characterization of the gene expression and the protein synthesis, as well as the enzymatic activity in the midgut, clearly demonstrated that (1) the chymotrypsin gene is newly transcribed after eclosion and the mRNA is present almost steadily during the digestion of a meal; (2) the chymotrypsin synthesis and its corresponding activity are induced and increased significantly by the ingestion of a meal. In vitro studies of the recombinant protease derived from the cDNA clone indicated several unique properties of the mosquito chymotrypsin compared with its bovine analog.