Abstract
Positive allosteric modulation of metabotropic glutamate receptor subtype 5 (mGlu5) is a promising novel approach for the treatment of schizophrenia and cognitive disorders. Allosteric binding sites are topographically distinct from the endogenous ligand (orthosteric) binding site, allowing for co-occupation of a single receptor with the endogenous ligand and an allosteric modulator. Negative allosteric modulators (NAMs) inhibit and positive allosteric modulators (PAMs) enhance the affinity and/or efficacy of the orthosteric agonist. The molecular determinants that govern mGlu5 modulator affinity versus cooperativity are not well understood. Focusing on the modulators based on the acetylene scaffold, we sought to determine the molecular interactions that contribute to PAM versus NAM pharmacology. Generation of a comparative model of the transmembrane-spanning region of mGlu5 served as a tool to predict and interpret the impact of mutations in this region. Application of an operational model of allosterism allowed for determination of PAM and NAM affinity estimates at receptor constructs that possessed no detectable radioligand binding as well as delineation of effects on affinity versus cooperativity. Novel mutations within the transmembrane domain (TM) regions were identified that had differential effects on acetylene PAMs versus 2-methyl-6-(phenylethynyl)-pyridine, a prototypical NAM. Three conserved amino acids (Y658, T780, and S808) and two nonconserved residues (P654 and A809) were identified as key determinants of PAM activity. Interestingly, we identified two point mutations in TMs 6 and 7 that, when mutated, engender a mode switch in the pharmacology of certain PAMs.
Footnotes
- Received November 21, 2012.
- Accepted February 25, 2013.
This work is supported by the National Institutes of Health National Institute of Mental Health [Grant 2R01-MH062646-13]; National Institutes of Health National Institute of Neurological Disorders and Stroke [Grant 2R01-NS031373-16A2]; National Institutes of Health National Institute on Drug Abuse [Grant 1R01-DA023947]; and Molecular Libraries Probe Production Centers Network [Grants 5 u54 MH84659-03 and 5 u54 MH84659-03S1]. K.J.G. is a recipient of a National Alliance for Research on Schizophrenia and Depression (NARSAD)–Maltz Young Investigator Award, an American Australian Association Merck Foundation Fellowship, and a National Health and Medical Research Council (Australia) Overseas Biomedical Postdoctoral Training Fellowship. Work in J.M.'s laboratory is supported through the National Institutes of Health [Grants R01-GM080403, R01-MH090192, and R01-GM099842] and the National Science Foundation [Career 0742762]. P.J.C. is a consultant for Seaside Therapeutic and receives research support from Seaside Therapeutics and Johnson and Johnson/Janssen Pharmaceutica.
↵This article has supplemental material available at molpharm.aspetjournals.org.
- Copyright © 2013 by The American Society for Pharmacology and Experimental Therapeutics
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