BPS2026 – Regulatory role of the L1-MX segment in the biogenesis of α7 nicotinic acetylcholine receptors

The homomeric α7 nicotinic acetylcholine receptor (α7nAChR) is expressed both within and outside the mammalian nervous system. As an ionotropic receptor and a member of the pentameric ligand-gated ion channel (pLGICs) superfamily, α7nAChR is highly permeable to calcium. It plays critical roles in synaptic transmission, synaptic plasticity, and cell signaling pathways. Dysregulation in the biogenesis of α7nAChR is associated with cognitive dysfunction. The involvement of the receptor in cancer cells promotes tumor growth and spreading. The biogenesis or functional surface expression of α7nAChR can be enhanced by the chaperone proteins RIC-3 and NACHO. Previously, we reported a binding motif required for RIC-3 in the 5-HT 3A receptor, another member of pLGICs. The conserved residues in this motif are also found within the L1-MX segment of the α7 nACh subunit. We, therefore, explored the regulatory roles of these conserved residues in the biogenesis of α7nAChR using multiple approaches, including heterologous expression in Xenopus laevis oocytes, mutagenesis, pull-down assays, biotinylation assays, and two-electrode voltage-clamp (TEVC) recordings. Here, we demonstrate that synthetic α7 L1-MX peptides interact with both RIC-3 and NACHO. We then show that Ala replacements within the L1-MX segment alter the expression profiles of α7 oligomers, which may negatively impact the surface expression. A single Ala replacement in L1-MX is sufficient to abolish the α7 currents observed in TEVC recordings. Current was recovered upon co-expression with NACHO. Our findings here position the L1-MX segment as a promising target for future drug development that can minimize adverse effects.