Structure of the G119S Mutant Acetylcholinesterase of the Malaria Vector Anopheles gambiae Reveals Basis of Insecticide Resistance

Abstract

Malaria is a devastating disease in sub-Saharan Africa and is transmitted by the mosquito Anopheles gambiae. While indoor residual spraying of anticholinesterase insecticides has been useful in controlling the spread of malaria, widespread application of these compounds has led to the rise of an insecticide-resistant mosquito strain that harbors a G119S mutation in the nervous system target enzyme acetylcholinesterase. We demonstrate the atomic basis of insecticide resistance through structure determination of the G119S mutant acetylcholinesterase of An. gambiae in the ligand-free state and bound to a potent difluoromethyl ketone inhibitor. These structures reveal specific features within the active-site gorge distinct from human acetylcholinesterase, including an open channel at the base of the gorge, and provide a means for improving species selectivity in the rational design of improved insecticides for malaria vector control.

A Second Look at the Crystal Structures of Drosophila melanogaster Acetylcholinesterase in Complex with Tacrine Derivatives Provides Insights Concerning Catalytic Intermediates and the Design of Specific Insecticides

“…Their overall structures are, nevertheless, very similar (1.9 Å rmsd) [8]. The structure of AgAChE notably confirmed the existence of an open channel at the base of the active-site gorge [9], as previously identified in DmAChE [6]. It is suggested that this particular structural feature could be exploited to design highly specific insecticides.…”

“…These structures provided the first rational basis for explaining differences in specificity and activity between DmAChE and mammalian AChEs. Recently, crystal structures of another insect AChE have been published, that of the wild type Anopheles gambiae AChE (AgAChE) [8] and of an insecticide-resistant mutant of the same enzyme [9]. The sequence similarity of AgAChE and DmAChE is relatively low (41.1% identity) since they are coded by non-homologous genes, ace-1 and ace-2, respectively [9].…”

“…In the present case study, close examination of both the electron Recently, crystal structures of another insect AChE have been published, that of the wild type Anopheles gambiae AChE (AgAChE) [8] and of an insecticide-resistant mutant of the same enzyme [9]. The sequence similarity of AgAChE and DmAChE is relatively low (41.1% identity) since they are coded by non-homologous genes, ace-1 and ace-2, respectively [9]. Their overall structures are, nevertheless, very similar (1.9 Å rmsd) [8].…”

Resistance to pirimiphos-methyl in West African Anopheles is spreading via duplication and introgression of the Ace1 locus

“…Studies in culicine and anopheline mosquitoes have found that non-synonymous mutations in Ace1 can result in resistance to carbamates and organophosphates other than pirimiphos-methyl (Weill et al 2003(Weill et al , 2004Feyereisen et al 2015). The most common mutation in Anopheles is a glycine to serine mutation in codon 280 (G280S, also known as G119S after the codon numbering of a partial crystal structure from the electric ray Torpedo californica (Weill et al 2003;Greenblatt et al 2004;Feyereisen et al 2015)), which is located near the active site gorge of ACE1 (Cheung et al 2018) and decreases its sensitivity to organophosphates and carbamates.…”

“…The most salient of these additional mutations was a serine-to-alanine SNP in codon 65 (S65A), with frequencies of 30-50% in multiple West African populations. Codon 65 maps to the anopheline-specific N-terminal insertion of ACE1 proteins (Supplementary Material SM1), which lacks predicted secondary structure and is far away from the active-site gorge of the enzyme (Cheung et al 2018). This position is not conserved across ACE1 orthologs, being variously encoded as alanine, serine or threonine in different Anopheles species (Supplementary Material SM1).…”