Cloning and characterization of cDNAS encoding carboxypeptidase-like proteins from the gut of Hessian fly larvae [Mayetiola destructor (Say)]

Transcriptomic analysis of the gut from Hessian fly larvae [Mayetiola destructor (Say)] identified nine cDNA clones that encode different carboxypeptidase-like proteins. Sequence comparison revealed that five of the nine cDNAs encoded very similar proteins with amino acid sequence identity over 96%. The other four cDNAs encoded diversified proteins with amino acid sequence identity less than 60%. Further sequence comparison with well characterized carboxypeptidases from other organisms revealed that these cDNAs encoded MDCP (M. destructor carboxypeptidase)-A1, MDCP-A2, MDCP-B, MDCP-BL, and MDCP-D. All residues characteristic of metallocarboxypeptidases including the HXXE motif were conserved among members. Northern blot analysis revealed various expression patterns for different gene groups in different developmental stages of M. destructor, suggesting that individual carboxypeptidases perform specific functions or have different specificities. Enzymatic activity assays demonstrated that both carboxypeptidases A and B are predominant in the larval stage, the only feeding stage of M. destructor, indicating a role in food digestion. The digestive role is further supported by the fact that 80% of the enzymatic activity in larvae occurred in the gut. Among these two types of enzymes, the activity of carboxypeptidase A was at least four times higher than that of carboxypeptidase B under the same conditions, suggesting that carboxypeptidase A is the major digestive enzyme in the gut of M. destructor larvae.