cDNA and deduced amino acid sequence of a blood meal-induced trypsin from the mosquito, Aedes aegypti

A cDNA for a midgut trypsin induced by a blood meal has been cloned and sequenced from the mosquito Aedes aegypti. The 862 base sequence codes for a 257 amino acid protein, which is presumably a trypsin precursor, since the sequence of purified mosquito trypsin begins at residue 26, immediately following an arginine residue in the precursor. The amino terminal 25 amino acids in the precursor are composed of a putative 15 amino acid signal peptide and a 10 amino acid activation peptide. Compared to vertebrate trypsinogens, the putative mosquito trysinogen lacks the four acidic amino acids immediately preceding the basic amino acid at the activation peptide cleavage site, suggesting the mechanism of its activation may be different from the activation of vertebrate trypsinogens. However, since a trypsinogen has not yet been isolated from the mosquito, these conclusions are tentative. The deduced amino acid sequence is homologous to that of other trypsins in those residues around the catalytic triad, and in several residues which are found only in trypsins. However, the sequence of the specificity pocket in mosquito trypsin, KESPC, differs from that found in other trypins, KDSC. The Asp is thought to bind the basic residue of the substrate, and the Glu in the mosquito trypsin may serve the same role. The changes in trypsin protein and mRNA levels following a blood meal indicate that an important component of the regulation of trypsin synthesis is at the transcriptional level.