The UNC-49 receptor is a Cys-loop GABA receptor that is unique to the nematode phylum. The receptor differs from mammalian GABA receptors both in amino acid sequence and pharmacology which highlights its potential as a novel anthelmintic target. Sequence differences within and near the various ligand-binding loops of the nematode receptor suggest that there could be structural differences compared to mammalian receptors that result in different pharmacological and functional features. Here we investigated three residues in the UNC-49 receptor from the parasitic nematode Haemonchus contortus: K181, E183, and T230. Analysis of these residues was conducted via site-directed mutagenesis, electrophysiology, MD simulations, and mutant cycling analysis. In the UNC-49 receptor, E183 lies in close proximity to K181 where together they appear to play a role in GABA sensitivity and pharmacology, possibly interacting via an ionic bond. While the introduction of single alanine residues at each position separately had a negative impact on GABA EC₅₀, the double alanine mutant (K181A/E183A) exhibited wildtype-level GABA EC₅₀ and some differences in pharmacology. Overall, this study has revealed a potentially novel role for these two residues in nematode UNC-49 GABA receptors that could aid in understanding their function.

UNC-49 受体是线虫门特有的 Cys 环 GABA 受体。该受体在氨基酸序列和药理学方面均不同于哺乳动物 GABA 受体，这突出了其作为新型驱虫靶标的潜力。线虫受体的各种配体结合环内和附近的序列差异表明，与哺乳动物受体相比可能存在结构差异，从而导致不同的药理学和功能特征。在这里，我们研究了来自寄生线虫捻转血矛线虫的 UNC-49 受体中的三个残基：K181、E183 和 T230。这些残留物的分析是通过定点诱变、电生理学、MD 模拟和突变循环分析进行的。在 UNC-49 受体中，E183 靠近 K181，它们一起似乎在 GABA 敏感性和药理学中发挥作用，可能通过离子键相互作用。虽然在每个位置分别引入单个丙氨酸残基对 GABA EC ₅₀有负面影响，但双丙氨酸突变体 (K181A/E183A) 表现出野生型水平的 GABA EC ₅₀和药理学上的一些差异。总的来说，这项研究揭示了这两个残基在线虫 UNC-49 GABA 受体中的潜在新作用，有助于了解它们的功能。