Association between the Arylalkylamine N-Acetyltransferase (AANAT) Gene and Seasonality in Patients with Bipolar Disorder

Backbone resonance assignments of dopamine N-acetyltransferase in free and cofactor-bound states

Dopamine N-acetyltransferase (Dat), belonging to the GCN5-related N-acetyltransferase (GNAT) superfamily, is an arylalkylamine N-acetyltransferase (AANAT) that is involved in insects neurotransmitter inactivation and the development of insect cuticle sclerotization. By using the cofactor acetyl coenzyme A (Ac-CoA) as an acetyl group donor, Dat produces acetyl-dopamine through the reaction with dopamine. Although AANATs share similar structural features with the GNAT family, they have low sequence identities among insect AANATs (~ 40%) and between insect AANATs and vertebrate AANATs (~ 12%). A common noticed feature in GNATs is the Ac-CoA-binding induced conformational change, and this is important for further selection and catalysis of its substrate. In AANATs, the conformational changes help the sequential binding mechanism. Here, we report the 1H, 13C and 15N backbone resonance assignments of the 24 kDa Dat from Drosophila melanogaster in the free and Ac-CoA-bound states, and the chemical shift differences revealed a significant conformational change in the α1 region of Dat. These assignments provide a foundation for further investigations of the catalysis and structural regulation of Dat in solution.

The identification of insect specific iAANAT inhibitors

An important aspect of food security is the development of innovative insecticides, particularly ones that specifically target insect pests and exhibit minimal toxicity to mammals. The insect arylalkylamine N-acyltransferases (iAANATs) could serve as targets for novel insecticides that satisfy these criteria. There exists a wealth of structural and biochemical information for the iAANATs and iAANAT knockdown experiments show that these enzymes are critical to insect health. Herein, we have expressed, purified, and characterized two new iAANATs, one from Apis mellifera (honey bee, AmNAT1) and another from Diaphorina citri (Asian citrus psyllid, DcNAT). We discovered that diminazene, a compound used to treat livestock for trypanosomiasis and babesiosis, inhibits AmNAT1, DcNAT, and D. melanogaster DmAgmNAT with modest affinity, Ki values ranging from 0.8 μM to 200 μM. We found a series of guanidines, amidines, and a hydroxamate, structurally related to diminazene, also inhibit the iAANATs, including camostat, gabexate, nafamostate, and panobinostat. Significantly, we found DmAgmNAT is far more susceptible to inhibition by four of these five of these compounds. In particular, camostat, nafamostat, and gabexate inhibit DmAgmNAT with Ki values of 0.2-30 μM, but no inhibition of AmNAT1 and DcNAT was observed at 500 μM for any of the three. These results show that a species-specific inhibitor targeted against an iAANAT is a real possibility. Also, we report that adipoyl-CoA is a substrate for AmNAT1 and DcNAT and that succinoyl-CoA is a substrate for DcNAT. These results contribute to a growing body of data suggesting that N-dicarboxyacyl-amines are metabolites in insects and other organisms.

Evaluation of Rhodanine Indolinones as AANAT Inhibitors

Circadian rhythm (CR) dysregulation negatively impacts health and contributes to mental disorders. The role of melatonin, a hormone intricately linked to CR, is still a subject of active study. The enzyme arylalkylamine N-acetyltransferase (AANAT) is responsible for melatonin synthesis, and it is a potential target for disorders that involve abnormally high melatonin levels, such as seasonal affective disorder (SAD). Current AANAT inhibitors suffer from poor cell permeability, selectivity, and/or potency. To address the latter, we have employed an X-ray crystal-based model to guide the modification of a previously described AANAT inhibitor, containing a rhodanine-indolinone core. We made various structural modifications to the core structure, including testing the importance of a carboxylic acid group thought to bind in the CoA site, and we evaluated these changes using MD simulations in conjunction with enzymatic assay data. Additionally, we tested three AANAT inhibitors in a zebrafish locomotion model to determine their effects in vivo. Key discoveries were that potency could be modestly improved by replacing a 5-carbon alkyl chain with rings and that the central rhodanine ring could be replaced by other heterocycles and maintain potency.