Oral Presentation 49th Lorne Conference on Protein Structure and Function 2024

Decoding AMYR and CTR Activation: Structural Insights for Obesity Therapeutics (#43)

Jian-Jun Cao 1 2 , Rachel Johnson 1 2 , Matthew Belousoff 1 2 , Yi-Lynn Liang 1 , Tracy Josephs 1 2 , Radostin Danev 3 , Denise Wootten 1 2 , Patrick Sexton 1 2
  1. Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
  2. ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
  3. Graduate School of Medicine, University of Tokyo, Bunkyo-ku, Tokyo, Japan

Obesity remains a global health challenge, demanding effective medicines for long-term sustained weight loss. Amylin receptor (AMYRs) agonists have emerged as promising candidates due to their roles in regulating satiety, blood glucose, and energy expenditure1.

AMYRs are heterodimers consisting of the calcitonin (CT) receptor (CTR) and one of three receptor activity-modifying proteins (RAMP1-3), yielding three different subtypes2. In addition, CTR can function in its monomeric form as well, which adds to the complexity of the functional outcomes of this receptor family. AMYRs each have high affinity and potency for the endogenous ligand Amy but lower affinity for CT relative to CTR. In contrast, CTR exhibits a reverse phenotype with higher affinity for CT than Amy. While selective CTR agonists have no independent effect on weight, combined activation of CTR and AMYRs by dual amylin and calcitonin receptor agonists (DACRAs) leads to superior weight loss over activation of AMYRs alone3. Thus, understanding the structural underpinnings of AMYR and CTR activation and agonist selectivity is crucial for drug discovery.

Through cryo-electron microscopy, we determined over 13 receptor structures in complex with different peptide agonists, which are all at resolution range of 2.0-2.5 Å. We firstly revealed distinct activation mechanisms of two endogenous agonists (CT and Amy) on AMYRs that cause divergent active receptor conformations. Amy features a unique structured "bypass" motif (residues 19-25) absent in CT, stabilizing the specific AMYR conformations, thereby selectively activating AMYRs over CTR4. By modifying the bypass motif, we next developed a new series of Amy-templated,  non-selective DACRAs, with San45 being an exemplar. Notably, San45, via its conjugated lipid modification at position 21, was anchored at the edge of the receptor transmembrane bundle, enabling a stable, alternative binding mode when bound to CTR, in addition to the bypass mode of binding to AMYR. This research sheds light on the intricate interplay between peptide structure and receptor activation, guiding the creation of potent and nonselective AMYR agonists. These insights hold promise for innovative solutions in the fight against obesity and its associated health risks.

  1. 1. Zakariassen, H. L.; John, L. M.; Lutz, T. A., Central control of energy balance by amylin and calcitonin receptor agonists and their potential for treatment of metabolic diseases. Basic Clin Pharmacol Toxicol 2020, 127 (3), 163-177.
  2. 2. Udawela, M.; Christopoulos, G.; Morfis, M.; Christopoulos, A.; Ye, S.; Tilakaratne, N.; Sexton, P. M., A critical role for the short intracellular C terminus in receptor activity-modifying protein function. Mol Pharmacol 2006, 70 (5), 1750-60.
  3. 3. Sonne, N.; Karsdal, M. A.; Henriksen, K., Mono and dual agonists of the amylin, calcitonin, and CGRP receptors and their potential in metabolic diseases. Mol Metab 2021, 46, 101109.
  4. 4. Cao, J.; Belousoff, M. J.; Liang, Y.-L.; Johnson, R. M.; Josephs, T. M.; Fletcher, M. M.; Christopoulos, A.; Hay, D. L.; Danev, R.; Wootten, D.; Sexton, P. M., A structural basis for amylin receptor phenotype. Science 2022, 375 (6587), eabm9609.
  5. 5. Cao, J., Belousoff, M.J., Gerrard, E. et al. Structural insight into selectivity of amylin and calcitonin receptor agonists. Nat Chem Biol 2023.