Structure of the Native Muscle-type Nicotinic Receptor and Inhibition by Snake Venom Toxins

Area of Science:

• Structural Biology
• Neuroscience
• Biochemistry

Background:

• The nicotinic acetylcholine receptor (nAChR) is a crucial pentameric ligand-gated ion channel.
• It mediates fast synaptic transmission at the neuromuscular junction and in the central nervous system.
• Dysfunction of nAChRs is linked to neurological disorders like congenital myasthenic syndromes.

Purpose of the Study:

• To determine the high-resolution structure of the muscle-type nicotinic acetylcholine receptor.
• To elucidate the mechanism of receptor closure and ligand binding.
• To provide a structural basis for understanding nAChR gating and associated diseases.

Main Methods:

• Purification of the native nAChR from Torpedo electric tissue.
• Functional reconstitution of the receptor in lipids for cryo-electron microscopy (cryo-EM).
• Stabilization of the receptor in a closed state using α-bungarotoxin.

Main Results:

• The study presents the first high-resolution cryo-EM structure of the muscle-type nAChR.
• α-Bungarotoxin binding at subunit interfaces was observed to sterically hinder acetylcholine binding.
• A closed gate, formed by hydrophobic residues, was identified within the ion-conducting pore, approximately 60 Å from the toxin binding sites.

Conclusions:

• The determined structure provides critical insights into the closed state of the nAChR.
• It offers a framework for understanding the gating mechanism of ligand-gated ion channels.
• This structural information can aid in understanding the molecular basis of congenital myasthenic syndromes caused by nAChR mutations.