RT Journal Article
SR Electronic
T1 Molecular Characterization of Binding Loop E in the Nematode Cys-Loop GABA Receptor
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 1289
OP 1297
DO 10.1124/mol.118.112821
VO 94
IS 5
A1 Ariel Kwaka
A1 Mohammad Hassan Khatami
A1 Joshua Foster
A1 Everett Cochrane
A1 Sarah A. Habibi
A1 Hendrick W. de Haan
A1 Sean G. Forrester
YR 2018
UL http://molpharm.aspetjournals.org/content/94/5/1289.abstract
AB Nematodes exhibit a vast array of cys-loop ligand-gated ion channels with unique pharmacologic characteristics. However, many of the structural components that govern the binding of various ligands are unknown. The nematode cys-loop GABA receptor uncoordinated 49 (UNC-49) is an important receptor found at neuromuscular junctions that plays an important role in the sinusoidal movement of worms. The unique pharmacologic features of this receptor suggest that there are structural differences in the agonist binding site when compared with 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 analyzed the interaction of various residues by molecular dynamic simulations. We 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.