title: Probing the metabotropic glutamate receptor 5 (mGlu₅) positive allosteric modulator (PAM) binding pocket: discovery of point mutations that engender a "molecular switch" in PAM pharmacology.
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.
authors: Department of Pharmacology and Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical Center, Nashville, TN 37232-0697, USA.
authors: Karen J
authors: KJ
authors: Gregory
authors: Elizabeth D
authors: ED
authors: Nguyen
authors: Sean D
authors: SD
authors: Reiff
authors: Emma F
authors: EF
authors: Squire
authors: Shaun R
authors: SR
authors: Stauffer
authors: Craig W
authors: CW
authors: Lindsley
authors: Jens
authors: J
authors: Meiler
authors: P Jeffrey
authors: PJ
authors: Conn
mesh_terms: D000480:Alkynes / Q000737:chemistry / Q000494:pharmacology*; D000494:Allosteric Regulation / Q000187:drug effects; D000495:Allosteric Site; D000596:Amino Acids / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D018698:Glutamic Acid / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D017354:Point Mutation; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics* / Q000378:metabolism; D014162:Transfection / Q000379:methods
chemical_list: D000480:Alkynes; D000596:Amino Acids; D008024:Ligands; D011725:Pyridines; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D018698:Glutamic Acid; C121465:6-methyl-2-(phenylethynyl)pyridine