Student Posters 51st Lorne Proteins Conference 2026

Title: Structural basis of bitopic ligands at the M1 muscarinic acetylcholine receptor. (#346)

JIAYIN ZHANG 1 2 , David Thal 1 2 , Jesse Mobbs 1 2 , Celine Valant 1
  1. Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, VIC, Australia
  2. ARC Centre for Cryo-Electron Microscopy of Membrane Proteins, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, VIC, Australia

The muscarinic acetylcholine receptors (mAChRs) are class A G protein coupled receptors (GPCRs) consisting of five subtypes (M1 to M5)All subtypes are activated by the endogenous neurotransmitter acetylcholine (ACh). The mAChRs are expressed in the central nervous system (CNS) and periphery, but mAChR subtypes differ in their tissue distribution and physiological function. In particular, the M1 mAChR subtype is highly expressed in all major areas of the forebrain and play a critical role in synaptic plasticity, and learning and memory processes, making it an attractive therapeutic target for Alzheimer’s disease (Lebois et al., 2018).

 

However, therapeutic targeting of the M1 mAChR using traditional orthosteric agonists has proven challenging due to the highly conserved residues in the orthosteric binding site across all five mAChR subtypes (Vuckovic et al., 2019). The poor selectivity of orthosteric ligands can result in unwanted off-target side effects that hinder clinical translation (Brannan et al., 2020). Targeting allosteric sites provides an alternative strategy because these sites are less conserved and spatially distinct from the orthosteric pocket. Nevertheless, M1-selective allosteric modulators have shown limited clinical success due to poor drug-like properties, insufficient pro-cognitive efficacy, and on-target cholinergic adverse effects (Mandai et al., 2025).

 

A promising alternative is the use of bitopic ligands, which combine orthosteric and allosteric pharmacophores into a single molecule (Valant et al., 2009). By simultaneously engaging both orthosteric and allosteric sites, bitopic ligands have the potential to achieve both high affinity and high subtype selectivity. Despite this promise, structural information about the mechanisms by which these bitopic ligands act on the M1 mAChR remains limited.

 

By utilizing cryo-EM and molecular pharmacology techniques, our lab aims to provide in-depth insights into the molecular mechanisms of bitopic ligand interactions at the M1 mAChR, such as the bitopic ligand TBPB. To date, the purification of the human M1 mAChR bound to TBPB in complex with a G-proteins (miniGsqi-β1γ2) and Nb35 and processing of the cryo-EM dataset have been completed, positioning the project at model building and real-space refinement stage.

  1. Lebois, E. P., Thorn, C., Edgerton, J. R., Popiolek, M., & Xi, S. (2018). Muscarinic receptor subtype distribution in the central nervous system and relevance to aging and Alzheimer’s disease. Neuropharmacology, 136, 362–373. https://doi.org/10.1016/j.neuropharm.2017.11.018
  2. Mandai, T., Simen, A. A., Laurenza, A., & Kimura, H. (2025). M1 receptor positive allosteric modulators discovery approaches. Trends in Pharmacological Sciences, 46(4), 298–302. https://doi.org/10.1016/j.tips.2025.03.001
  3. Valant, C., Sexton, P. M., & Christopoulos, A. (2009). Orthosteric/Allosteric Bitopic Ligands: Going Hybrid at GPCRs. Molecular Interventions, 9(3), 125–135. https://doi.org/10.1124/mi.9.3.6
  4. Vuckovic, Z., Gentry, P. R., Berizzi, A. E., Hirata, K., Varghese, S., Thompson, G., van der Westhuizen, E. T., Burger, W. A. C., Rahmani, R., Valant, C., Langmead, C. J., Lindsley, C. W., Baell, J. B., Tobin, A. B., Sexton, P. M., Christopoulos, A., & Thal, D. M. (2019). Crystal structure of the M5 muscarinic acetylcholine receptor. Proceedings of the National Academy of Sciences of the United States of America, 116(51), 26001–26007. https://doi.org/10.1073/pnas.1914446116