title: Ancestral reconstruction of the ligand-binding pocket of Family C G protein-coupled receptors.
abstract: The metabotropic glutamate receptors (mGluRs) within the Family C subclass of G protein-coupled receptors are crucial modulators of synaptic transmission. However, their closest relatives include a diverse group of sensory receptors whose biological functions are not associated with neurotransmission, raising the question of the evolutionary origin of amino acid-binding Family C receptors. A common feature of most, if not all, functional Family C receptors is the presence of an amino acid-binding site localized within the large extracellular Venus flytrap domain. Here, we used maximum likelihood methods to infer the ancestral state of key residues in the amino acid-binding pocket of a primordial Family C receptor. These residues were reconstructed in the background of the fish 5.24 chemosensory receptor, a broad-spectrum amino acid-activated receptor. Unlike the WT 5.24 receptor, which was not activated by mGluR agonists and displayed low sensitivity toward l-glutamate, the reconstructed ancestral receptor possessed a pharmacological profile characterized by high affinity for both l-glutamate and selective Group I mGluR agonists. This pharmacological phenotype could be largely recapitulated by mutating only two residues in the 5.24 receptor-binding pocket. Our results suggest that this primordial Family C receptor may have arisen early in metazoan evolution and that it already was preadapted as a glutamate receptor for its later use at excitatory synapses in glutamate-mediated neurotransmission.
authors.affiliation: Departments of Pharmaceutical Sciences, Pharmacology, Ecology and Evolutionary Biology, and Cell and Systems Biology, University of Toronto, Toronto, ON, Canada M5S 3M2.
authors.forename: Donghui
authors.initials: D
authors.lastname: Kuang
authors.forename: Yi
authors.initials: Y
authors.lastname: Yao
authors.forename: David
authors.initials: D
authors.lastname: Maclean
authors.forename: Minghua
authors.initials: M
authors.lastname: Wang
authors.forename: David R
authors.initials: DR
authors.lastname: Hampson
authors.forename: Belinda S W
authors.initials: BS
authors.lastname: Chang
mesh_terms: D000818:Animals; D001665:Binding Sites; D005075:Biological Evolution; D002628:Chemoreceptor Cells / Q000737:chemistry; D005399:Fishes; D018698:Glutamic Acid / Q000378:metabolism; D016013:Likelihood Functions; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010641:Phenotype; D010802:Phylogeny; D051381:Rats; D018094:Receptors, Metabotropic Glutamate / Q000737:chemistry* / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D018094:Receptors, Metabotropic Glutamate; D018698:Glutamic Acid