[3H]Benzophenone photolabeling identifies state-dependent changes in nicotinic acetylcholine receptor structure

Area of Science:

• Neuroscience
• Pharmacology
• Biochemistry

Background:

• The nicotinic acetylcholine receptor (nAChR) is a crucial ion channel involved in neurotransmission.
• Benzophenone (BP) is a compound known to interact with biological systems, but its specific interactions with nAChRs require detailed characterization.
• Understanding nAChR ligand interactions is vital for developing targeted therapeutics.

Purpose of the Study:

• To characterize the interactions of benzophenone (BP) with the Torpedo nicotinic acetylcholine receptor (nAChR).
• To identify the specific amino acid residues involved in BP binding sites within the nAChR.
• To elucidate structural differences in the nAChR transmembrane domain between closed and desensitized states.

Main Methods:

• Electrophysiological analyses were performed on nAChRs expressed in Xenopus oocytes.
• Radioligand binding assays used [3H]tetracaine to assess BP's effect on antagonist binding.
• Photolabeling of nAChR-rich membranes with [3H]BP followed by UV irradiation identified covalent binding sites.

Main Results:

• BP acts as a low-potency noncompetitive antagonist of nAChRs, inhibiting acetylcholine responses and [3H]tetracaine binding.
• Photolabeling revealed [3H]BP incorporation into nAChR subunits (delta > alpha ≈ beta > gamma) within the transmembrane domain.
• Specific labeling patterns in the delta, beta, and gamma subunits differed between closed and desensitized receptor states, particularly near the M1-M3 helices and at the lipid interface.

Conclusions:

• BP binds to the nAChR transmembrane domain, acting as a noncompetitive antagonist.
• The study precisely maps BP binding sites, providing insights into the nAChR's allosteric modulation.
• Distinct labeling patterns highlight conformational changes in the nAChR transmembrane domain associated with receptor desensitization.