Biochemical Evolution of a Potent Target of Mosquito Larvicide, 3-Hydroxykynurenine Transaminase

Abstract

A specific mosquito enzyme, 3-hydroxykynurenine transaminase (HKT), is involved in the processing of toxic metabolic intermediates of the tryptophan metabolic pathway. The HKT enzymatic product, xanthurenic acid, is required for Plasmodium spp. development in the mosquito vectors. Therefore, an inhibitor of HKT may not only be a mosquitocide but also a malaria-transmission blocker. In this work, we present a study investigating the evolution of HKT, which is a lineage-specific duplication of an alanine glyoxylate aminotransferases (AGT) in mosquitoes. Synteny analyses, together with the phylogenetic history of the AGT family, suggests that HKT and the mosquito AGTs are paralogous that were formed via a duplication event in their common ancestor. Furthermore, 41 amino acid sites with significant evidence of positive selection were identified, which could be responsible for biochemical and functional evolution and the stability of conformational stabilization. To get a deeper understanding of the evolution of ligands’ capacity and the ligand-binding mechanism of HKT, the sequence and the 3D homology model of the common ancestor of HKT and AGT in mosquitoes, ancestral mosquito AGT (AncMosqAGT), were inferred and built. The homology model along with 3-hydroxykynurenine, kynurenine, and alanine were used in docking experiments to predict the binding capacity and ligand-binding mode of the new substrates related to toxic metabolites detoxification. Our study provides evidence for the dramatic biochemical evolution of the key detoxifying enzyme and provides potential sites that could hinder the detoxification function, which may be used in mosquito larvicide and design.

Inhibition of 3-Hydroxykynurenine Transaminase from Aedes aegypti and Anopheles gambiae: A Mosquito-Specific Target to Combat the Transmission of Arboviruses

“…Furthermore, only AeHKT exhibits AGT activity, i.e., the ability to catalyze the transamination of alanine in the presence of glyoxylate as an amino group acceptor, indicative of evolutionary divergence. 29 , 30 Therefore, the low sequence identity and dissimilar three-dimensional structure make the HsKATs an unlikely target for AeHKT inhibitors.…”

“…A comprehensive evolutive investigation of the HKT and AGT enzyme families supports a paralogous relation among these enzymes. 29 HKT is only found in mosquitoes, being the only AGT homologue involved in the detoxification of 3-HK. Therefore, HKT likely originated from gene duplication of mosquito AGT in a common ancestral.…”

“…Therefore, HKT likely originated from gene duplication of mosquito AGT in a common ancestral. 29 Furthermore, mosquito-specific HKT is the only AGT homologue involved in detoxification of 3-HK, and it is only found in mosquitoes. The enzymes kynureninase and L-kynurenine aminotransferases are responsible for metabolizing 3-HK in other insects and mammals.…”

“…The enzymes kynureninase and L-kynurenine aminotransferases are responsible for metabolizing 3-HK in other insects and mammals. 29 …”

“…(C) Detail of the identical active site residues for superimposed X-ray structures of B (chain A). A common ancestor between AGT and HKT was duplicated to create HKT, as indicated by Chen et al29 Consequently, the functional variations between 6MFB and 2HUF, where the only active site mismatch is between positions A78 and G79, seem to be due to substrate recognition rather than active site polymorphism. Alignment and a portion of the analysis had been completed with the ENDscript webserver 31.…”