Regulation of Expression and Function of Neuronal Nicotinic Receptors by Accessory Subunits

Nicotine binds to nicotinic acetylcholine receptors (nAChRs) and perturbs the biogenesis and trafficking of these channels. The α4β2 and α3β4 subtypes are the most abundantly expressed nAChRs in the central and peripheral nervous system, respectively, and are key mediators of nicotine dependence and withdrawal. These nAChRs are heteropentameric ligand-gated ion channels that form into two stoichiometries in the absence of other subunits: 3α:2β and 2α:3β; each of these contains two canonical ligand binding sites formed by the primary surface of α-subunit and an adjacent β-subunit. Nicotine exposure leads to the upregulation of the 2α:3β stoichiometry only. The only structural difference between the two stoichiometries is the subunit at the accessory position - either α or β. However, it is unknown if this structural nuance yields any biophysical differences to the overall channel function and expression. We aimed to investigate the mechanism by which nicotine modulates differential expression of α4β2 nAChRs in mammalian cells. Our studies revealed that nicotine promotes the surface expression of (α4)2(β2)3 by overcoming the effects of a native chaperone protein that otherwise facilitates (α4)3(β2)2 trafficking. Furthermore, we hypothesized that in the (α3)3(β4)2 stoichiometry, the α3 accessory subunit forms a third ligand binding site as observed in the paralogous α4β2 nAChR. To study this, we engineered a tandem dimer of α3β4 to restrict the stoichiometry and probe separable ligand binding properties using a substituted-cysteine accessibility method followed by covalent modification. This approach identified a third ligand binding site unique to the (α3)3(β4)2 stoichiometry at the α3 accessory interface that is crucial for channel activation. Understanding the stoichiometric differences in nAChRs will inform future precision drug design to target nicotine withdrawal, with the goal of alleviating symptoms while preserving the normal functions.

Author dc:creator

• Gauri C Kulkarni (23291551)

• Biomedical Sciences
• Neurobiology

Statement dc:rights

• In Copyright

DOI dc:identifier

https://doi.org/10.25417/uic.31451329.v1

OAI identifier oai:identifier

oai:figshare.com:article/31451329