The arylalkylamine N-acyltransferases (AANATs) are enzymes that catalyze the acyl-CoA-dependent formation of N-acylarylalkylamides: acyl-CoA + arylalkylamine → N-acylarylalkylamides + CoA-SH. Herein, we describe our study of a previously uncharacterized AANAT from Bombyx mori: Bm-iAANAT3. Bm-iAANAT3 catalyzes the direct formation of N-acylarylalkylamides and accepts a broad range of short-chain acyl-CoA thioesters and amines as substrates. Acyl-CoA thioesters possessing an acyl chain length >10 carbon atoms are not substrates for Bm-iAANAT3. We report that Bm-iAANAT3 is a “versatile generalist”, most likely, functioning in amine acetylation – a reaction in amine inactivation/excretion, cuticle sclerotization, and melanism. We propose a kinetic and chemical mechanism for Bm-iAANAT3 that is consistent with our steady-state kinetic analysis, dead-end inhibition studies, determination of the pH-rate profiles, and site-directed mutagenesis of a catalytically important amino acid in Bm-iAANAT3. These mechanistic studies of Bm-iAANAT3 will foster the development of novel compounds targeted against this enzyme and other insect AANATs for the control of insect pests.

Arylalkylamine N-acyltransferases (AANATs) catalyze the formation of an N-acylamide from an acyl-CoA thioester and an amine. One well known example is the production of N-acetylserotonin from acetyl-CoA and serotonin, a reaction in the melatonin biosynthetic pathway from tryptophan. AANATs have been identified from a variety of vertebrates and invertebrates. Considerable efforts have been devoted to the mammalian AANAT because a cell-permeable inhibitor specifically targeted against this enzyme could prove useful to treat diseases related to dysfunction in melatonin production. Insects are an interesting model for the study of AANATs because more than one isoform is typically expressed by a specific insect and the different insect AANATs (iAANATs) serve different roles in the insect cell. In contrast, mammals express only one AANAT. The major role of iAANATs seem to be in the production of N-acetyldopamine, a reaction important in the tanning and sclerotization of the cuticle. Metabolites identified in insects including N-acetylserotonin and long-chain N-fatty acyl derivatives of dopamine, histidine, phenylalanine, serotonin, tyrosine, and tryptophan are likely produced by an iAANAT. In vitro studies of specific iAANATs are consistent with this hypothesis. In this review, we highlight the current metabolomic knowledge of the N-acylated aromatic amino acids and N-acylated derivatives of the aromatic amino acids, the current mechanistic understanding of the iAANATs, and explore the possibility that iAANATs serve as insect “rhymezymes” regulating photoperiodism and other rhythmic processes in insects.

The growing issue of insecticide resistance has meant the identification of novel insecticide targets has never been more important. Arylalkylamine N-acyltransferases (AANATs) have been suggested as a potential new target. These promiscuous enzymes are involved in the N-acylation of biogenic amines to form N-acylamides. In insects, this process is a key step in melanism, hardening of the cuticle, removal of biogenic amines, and in the biosynthesis of fatty acid amides. The unique nature of each AANAT isoform characterized indicates each organism accommodates an assembly of discrete AANATs relatively exclusive to that organism. This implies a high potential for selectivity in insecticide design, while also maintaining polypharmacology. Presented here is a thorough kinetic and structural analysis of AANAT found in one of the most common secondary pests of all plant commodities in the world, Tribolium castaneum. The enzyme, named TcAANAT0, catalyzes the formation of short-chain N-acylarylalkylamines, with short-chain acyl-CoAs (C2–C10), benzoyl-CoA, and succinyl-CoA functioning in the role of acyl donor. Recombinant TcAANAT0 was expressed and purified from E. coli and was used to investigate the kinetic and chemical mechanism of catalysis. The kinetic mechanism is an ordered sequential mechanism with the acyl-CoA binding first. pH-rate profiles and site-directed mutagenesis studies identified amino acids critical to catalysis, providing insights about the chemical mechanism of TcAANAT0. A crystal structure was obtained for TcAANAT0 bound to acetyl-CoA, revealing valuable information about its active site. This combination of kinetic analysis and crystallography alongside mutagenesis and sequence analysis shines light on some approaches possible for targeting TcAANAT0 and other AANATs for novel insecticide design.

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Fatty acid amides are a diverse family of underappreciated, biologically occurring lipids. Herein, the methods for the chemical synthesis and subsequent characterization of specific members of the fatty acid amide family are described. The synthetically prepared fatty acid amides and those obtained commercially are used as standards for the characterization and quantification of the fatty acid amides produced by biological systems, a fatty acid amidome. The fatty acid amidomes from mouse N18TG2 cells, sheep choroid plexus cells, Drosophila melanogaster, Bombyx mori, Apis mellifera, and Tribolium castaneum are presented.