Isolation and sequencing of cDNA clones coding for juvenile hormone esterase from Heliothis virescens. Evidence for a catalytic mechanism for the serine carboxylesterases different from that of the serine proteases.

Three cDNA clones containing the entire coding sequence for JH esterase from the noctuid moth Heliothis virescens have been isolated from an expression library using specific antibodies and oligonucleotide probes. The complete sequence of one of the clones shows a 2989-base pair insert that is approximately the length of the single 3.0-kilobase pair mRNA transcript detected by Northern blotting. The clone has an open reading frame of 1714 base pairs that predicts a mature protein (minus signal peptide 19 residues long) of 61,012 Da. The 3'-nontranslated region has three signals for polyadenylation although only one apparently is used. Edman degradation of purified juvenile hormone lesterase indicates two slightly different proteins (one being 75% of the total) while the three cDNA clones differ at three bases in their 5' region causing their predicted sequence to differ at one or two residues of the 35 amino acids sequenced from the major form. Comparison of the predicted protein sequence to other carboxylesterase sequences indicates extensive similarity in the NH2-terminal half of the protein and the active site serine to be at position 201. The lack of conserved histidine and aspartate residues and the presence of conserved arginine and glutamate residues in appropriate positions in the NH2-terminal half of the homologous serine carboxylesterases suggests a catalytic mechanism for the serine carboxylesterases that is different from that of the serine proteases.