Molecular Characterization of Binding Loop E in the Nematode Cys-Loop GABA Receptor.

Area of Science:

• Neuroscience
• Molecular Biology
• Parasitology

Background:

• Nematodes possess diverse cys-loop ligand-gated ion channels with distinct pharmacological profiles.
• The nematode UNC-49 GABA receptor is crucial for neuromuscular function and worm locomotion.
• Structural insights into nematode GABA receptor ligand binding are limited.

Purpose of the Study:

• To investigate structural differences in the agonist binding loop (loop E) of the nematode UNC-49 GABA receptor.
• To identify specific amino acid residues involved in ligand binding and their functional consequences.
• To explore potential targets for novel anthelmintic drug development.

Main Methods:

• Substituted cysteine accessibility method (SCAM) was used to probe amino acid accessibility in loop E.
• Molecular dynamics simulations were employed to analyze residue interactions.
• Functional analysis of receptor mutants assessed changes in GABA sensitivity (EC50) and current (IGABA).

Main Results:

• Mutations H142C, R147C, and S157C in loop E significantly altered GABA EC50 values.
• These mutants showed accessibility to MTSET, indicating solvent exposure.
• The unique residue H142 in nematode UNC-49 negatively impacts GABA sensitivity; its mutation increased sensitivity and altered DAVA agonism.

Conclusions:

• Structural variations exist in the agonist binding pocket of nematode UNC-49 compared to mammalian GABA receptors.
• Specific residues, particularly H142, play critical roles in modulating GABA receptor function.
• These findings provide a basis for designing targeted anthelmintics by exploiting nematode-specific receptor structures.