Dynamic ligand binding of dualsteric (allosteric/orthosteric) molecular probes controls the graded activation of muscarinic acetylcholine receptors

We investigated a class of bitopic (dualsteric) ligands of the M2 acetylcholine muscarinic receptor (M2AChR), i.e. compounds whose pharmacophoric groups are able to target the orthosteric as well as the allosteric binding site of the receptor.1,2 These model derivatives are composed of an allosteric fragment, an intermediate linker and an orthosteric moiety. As an example, ligands 1 and 2 incorporate the molecular portion of the allosteric compound Naphmethonium and the potent muscarinic agonist Iperoxo, which are connected by a flexible or a rigidified spacer group, respectively (Figure 1). These bipharmacophoric molecular probes were found to switch between two different binding orientations, resulting in both active and inactive populations of receptors bound by a given ligand, a behavior that has been termed dynamic ligand binding.3 Figure 1 In this study, pharmacological data analysis and computational simulations based on active and inactive M2AChR crystal structures led to identify two distinct binding topographies in a group of dualsteric partial agonists. One binding mode, which resembled that of the co-crystallized orthosteric ligand Iperoxo, engendered an agonist response. Conversely, dualsteric ligands binding to the allosteric site only showed a receptor-complex comparable to that of allosteric modulators. Thus, the observed agonist efficacies depended on the fraction of dualsteric (i.e. active) vs. purely allosteric (i.e. inactive) binding modes.4 References 1. Antony, J.; Kellershon, K.; Mohr-Andrä, M.; Kebig, A.; Prilla, S.; Muth, M.; Heller, E.; Disingrini, T.; Dallanoce, C.; Bertoni, S.; Schrobang, J.; Tränkle, C.; Kostenis, E.; Christopoulos, A.; Höltje, H.-D.; Barocelli, E.; De Amici, M.; Holzgrabe, U.; Mohr, K. FASEB J. 2009, 23, 442-450. 2. Bock, A.; Merten, N.; Schrage, R.; Dallanoce, C.; Bätz, J.; Klöckner, J.; Schmitz, J.; Matera, C.; Simon, K.; Kebig, A.; Peters, L.; Müller, A.; Schrobang-Ley, J.; Tränkle, C.; Hoffmann, C.; De Amici, M.; Holzgrabe, U.; Kostenis, E.; Mohr; K. Nat. Commun. 2012, 3:1044, doi: 10.1038/ncomms2028. 3. Bock, A.; Chirinda, B.; Krebs, F.; Messerer, R.; Bätz, J.; Muth, M.; Dallanoce, C.; Klingenthal, D.; Tränkle, C.; Hoffmann, C.; De Amici, M.; Holzgrabe, U.; Kostenis, E.; Mohr, K. Nat. Chem. Biol. 2014, 10, 18-20. 4. Bock, A.; Bermudez, M.; Krebs, F.; Matera, C.; Chirinda, B.; Sydow, D.; Dallanoce, C.; Holzgrabe, H.; De Amici, M.; Lohse, M.; Wolber, G.; Mohr, K. J. Biol. Chem., in press.