Poster Presentation The 47th Lorne Conference on Protein Structure and Function 2022

Structure of xanomeline bound M4 muscarinic acetylcholine reveals an unexpected dual orthosteric and allosteric binding profile (#132)

Wessel A. C. Burger 1 2 , Ziva Vuckovic 2 , Vi Pham 2 , Jesse I Mobbs 1 2 , Alisa Glukhova 3 , Patrick M Sexton 1 2 , Rado Danev 4 , Arthur Christopoulos 1 2 , Celine Valant 2 , David M Thal 1 2
  1. ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Vic, Australia
  2. Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Australia
  3. Structural Biology Division, Walter and Eliza Hall of Medical Research, Parkville, VIC, Australia
  4. Graduate School of Medicine, University of Tokyo, Tokyo, Japan

The five human muscarinic acetylcholine receptors (M1-M5 mAChRs) are an important family of class A G protein-coupled receptors (GPCRs) that are activated by the neurotransmitter acetylcholine. Within the mAChR family, the M4 subtype has emerged as a drug target of high therapeutic interest due to its expression in regions of the brain that are rich in dopamine and dopamine receptors1. Multiple studies have implicated the M4 mAChR in regulating dopaminergic neurons that are involved in cognition and addiction. Excitingly the drug xanomeline, has recently shown significant benefits in a phase II clinical trial for schizophrenia2. Notably, xanomeline displays a complex and unique pharmacological profile. For example, xanomeline binds to all five mAChR subtypes with similar binding affinity, however, its shows functional selectivity for the M4 mAChR. Xanomeline also displays persistent binding profile that is wash-resistant, as well as a unique interaction with positive allosteric modulators at the M2 mAChR subtype that does not take place with other orthosteric agonists, or at other mAChR subtypes3,4. To gain structural insight into the unique pharmacological properties of xanomeline, we obtained a cryo-EM structure of xanomeline bound to the M4 mAChR together with its transducer partner, the heterotrimeric Gi protein. Unexpectedly, xanomeline was found to occupy both the orthosteric and canonical mAChR allosteric binding site. Further pharmacological interrogation revealed xanomeline can act as an allosteric modulator and that its unique interaction with allosteric modulators at the M2 mAChR is likely due to a competitive interaction that occur in the allosteric binding site. Understanding the complex molecular mechanisms of xanomeline is expected to aid the development of further improved M4 mAChR selective compounds.

 

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