PT  - JOURNAL ARTICLE
AU  - Ariel Kwaka
AU  - Mohammad H Khatami
AU  - Joshua Foster
AU  - Everett Cochrane
AU  - Sarah A Habibi
AU  - Hendrick W de Haan
AU  - Sean G Forrester
TI  - Molecular characterization of binding loop E in the nematode cys-loop GABA receptor
AID  - 10.1124/mol.118.112821
DP  - 2018 Jan 01
TA  - Molecular Pharmacology
PG  - mol.118.112821
4099  - http://molpharm.aspetjournals.org/content/early/2018/09/07/mol.118.112821.short
4100  - http://molpharm.aspetjournals.org/content/early/2018/09/07/mol.118.112821.full
AB  - Nematodes exhibit a vast array of cys-loop ligand-gated ion channels with unique pharmacological characteristics. However, many of the structural components that govern the binding of various ligands are unknown. The nematode cys-loop GABA receptor UNC-49 is an important receptor found at neuromuscular junctions, and plays an important role in the sinusoidal movement of worms. The unique pharmacology of this receptor suggests that there are structural differences in the agonist binding site when compared to mammalian receptors. In this study, we examined each amino acid in one of the main agonist binding loops (loop E) via the substituted cysteine accessibility method (SCAM) and analysed the interaction of various residues by molecular dynamic simulations. It was found that of the 18 loop E mutants analyzed, H142C, R147C and S157C had significant changes in GABA EC50 and were accessible to modification by a methanethiosulfonate reagent (MTSET) resulting in a change in IGABA. In addition, the residue H142, which is unique to nematode UNC-49 GABA receptors, appears to play a negative role in GABA sensitivity as its mutation to cysteine increased sensitivity to GABA and caused the UNC-49 receptor partial agonist 5-aminovaleric acid (DAVA) to behave as a full agonist. Overall, this study has revealed potential differences in the agonist binding pocket between nematode UNC-49 and mammalian GABA receptors that could be exploited in the design of novel anthelmintics.