A lepidopteran aminoacylase (L-ACY-1) in Heliothis virescens (Lepidoptera: Noctuidae) gut lumen hydrolyzes fatty acid-amino acid conjugates, elicitors of plant defense

Abstract

Fatty acid-amino acid conjugates (FACs) have been identified in Lepidopteran larvae as elicitors of plant defenses. Plant responses include the production of primary defense compounds and induction of secondary defense strategies including attraction of parasitoid wasps. These elicitors are present despite fitness costs, suggesting that they are important for the larvae's survival. In order to exploit FAC-mediated plant defense responses in agricultural settings, an understanding of FAC purpose and metabolism is crucial. To clarify their role, enzymes involved in this metabolism are being investigated. In this work a previously undiscovered FAC hydrolase was purified from Heliothis virescens frass by liquid chromatography and PAGE techniques and was identified as an aminoacylase-like protein (L-ACY-1) using MALDI-ToF/ToF and Edman sequencing. The full length gene was cloned and expressed in Escherichia coli and a polyclonal antibody against L-ACY-1 was made. L-ACY-1 was confirmed to be responsible for FAC hydrolysis activity through inhibition of N-linolenoyl-l-glutamine hydrolysis by titration with the polyclonal anti-L-ACY-1 antibody. L-ACY-1 activity is dependent on a divalent cation. This is the first time an aminoacylase has been described from an insect. L-ACY-1 appears to play a vastly different role in insects than ACYs do in mammals and may be involved in maintaining glutamine supplies for gut tissue metabolism. Identification of L-ACY-1, a FAC hydrolase, clarifies a previously uncharacterized portion of FAC metabolism.