Student Posters 51st Lorne Proteins Conference 2026

The muscarinic acetylcholine receptors (mAChRs) are a five-membered (M₁–M₅) subfamily of G protein-coupled receptors (GPCRs) that are activated by the neurotransmitter acetylcholine (ACh). The M₁, M₄, and M₅ mAChRs have emerged as attractive drug targets for the treatment of various central nervous system disorders, such as Alzheimer’s disease (AD) at the M₁ mAChR. However, designing subtype-selective ligands is challenging due to the high sequence similarity of the ACh binding site (orthosteric site) that is present across all mAChR subtypes [1]. The alternative approach is to target comparatively less conserved binding site, known as ‘allosteric binding site’. Over the past several years, a number of M₁ selective positive allosteric modulators (PAM) have been developed that can modulate the binding and the activity of the co-bound orthosteric agonist. The selectivity is achieved via utilising a set of both conserved and non-conserved residues that form part of the allosteric network.

The goal of this project is to determine how allosteric modulators achieve subtype selectivity utilising both conserved and non-conserved residues within the allosteric network.

In our project, both pharmacological and structural approaches have demonstrated that the selectivity of M₁ and M₄ mAChR PAMs arises largely through their differential engagement with non-conserved residues that form part of an allosteric network consisting of non-conserved and conserved residues linking the allosteric and orthosteric binding sites. Swapping six non-conserved residues in the allosteric network between M₁ and M₄ mAChR subtypes altered the selectivity profile for the M₁ and M₄ mAChRs selective PAMs, BQCA and LY2033298, respectively. Furthermore, the cryo-EM structures of M₁ mAChR, M₁-hextuplet, M₄ mAChR and M₄-hextuplet receptors in complex with allosteric ligands reveal the binding poses and key molecular interactions of the ligands to the receptor and reveal distinct sets of interactions, specific to cooperativity-mediated selectivity (driving cooperativity)

1. Vuckovic, Z., et al., Crystal structure of the M₅ muscarinic acetylcholine receptor.