Functional validation of novel levamisole resistance marker S168T in Haemonchus contortus

Abstract

Recently, a S168T variant in the acetylcholine receptor subunit ACR-8 was associated with levamisole resistance in the parasitic helminth Haemonchus contortus. Here, we used the Xenopus laevis oocyte expression system and two-electrode voltage-clamp electrophysiology to measure the functional impact of this S168T variant on the H. contortus levamisole-sensitive acetylcholine receptor, L-AChR-1.1. Expression of the ACR-8 S168T variant significantly reduced the current amplitude elicited by levamisole compared to acetylcholine, with levamisole changing from a full to partial agonist on the recombinant L-AChR. Functional validation of the S168T mutation on modulating levamisole activity at the receptor level highlights its critical importance as both a mechanism and a marker of levamisole resistance.

Keywords: Acetylcholine receptor; Functional validation; Haemonchus contortus; Levamisole resistance; Resistance mechanism; S168T.

Graphical abstract

Fig. 1

Concentration-response curves of ACh (black) and LEV (red) on the Haemonchus contortus “wild-type” L-AChR-1.1 receptor (A), on the L-AChR-1.1 with the S168T Hco-ACR-8 replacing the wild-type Hco-ACR-8 subunit (“homozygous mutant”) (B), and on the L-AChR-1.1 with S168T Hco-ACR-8 and wild-type Hco-ACR-8 at a 1:1 relative ratio (“heterozygous mutant”) (C). All responses were normalized to 100 μM ACh. The data shown represents mean ± SEM. Sample sizes are shown in Table 1.