title: Determinants of endogenous ligand specificity divergence among metabotropic glutamate receptors.
abstract: To determine the structural origins of diverse ligand response specificities among metabotropic glutamate receptors (mGluRs), we combined computational approaches with mutagenesis and ligand response assays to identify specificity-determining residues in the group I receptor, mGluR1, and the group III receptors, mGluR4 and mGluR7. Among these, mGluR1 responds to L-glutamate effectively, whereas it binds weakly to another endogenous ligand, L-serine-O-phosphate (L-SOP), which antagonizes the effects of L-glutamate. In contrast, mGluR4 has in common with other group III mGluR that it is activated with higher potency and efficacy by L-SOP. mGluR7 differs from mGluR4 and other group III mGluR in that L-glutamate and L-SOP activate it with low potency and efficacy. Enhanced versions of the evolutionary trace (ET) algorithm were used to identify residues that when swapped between mGluR1 and mGluR4 increased the potency of L-SOP inhibition relative to the potency of L-glutamate activation in mGluR1 mutants and others that diminished the potency/efficacy of L-SOP for mGluR4 mutants. In addition, combining ET identified swaps from mGluR4 with one identified by computational docking produced mGluR7 mutants that respond with dramatically enhanced potency/efficacy to L-SOP. These results reveal that an early functional divergence between group I/II and group III involved variation at positions primarily at allosteric sites located outside of binding pockets, whereas a later divergence within group III occurred through sequence variation both at the ligand-binding pocket and at loops near the dimerization interface and interlobe hinge region. They also demonstrate the power of ET for identifying allosteric determinants of evolutionary importance.
authors.affiliation: From the Graduate Program in Structural and Computational Biology and Molecular Biophysics.
authors.forename: Hye Jin
authors.initials: HJ
authors.lastname: Kang
authors.affiliation: the Department of Molecular and Human Genetics, and.
authors.forename: Angela D
authors.initials: AD
authors.lastname: Wilkins
authors.affiliation: From the Graduate Program in Structural and Computational Biology and Molecular Biophysics, the Department of Molecular and Human Genetics, and the Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030.
authors.forename: Olivier
authors.initials: O
authors.lastname: Lichtarge
authors.affiliation: From the Graduate Program in Structural and Computational Biology and Molecular Biophysics, the Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030 twensel@bcm.edu.
authors.forename: Theodore G
authors.initials: TG
authors.lastname: Wensel
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism; D019295:Computational Biology; D019143:Evolution, Molecular; D057809:HEK293 Cells; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D017433:Protein Structure, Secondary; D018094:Receptors, Metabotropic Glutamate / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology
chemical_list: D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; D002118:Calcium; C108823:metabotropic glutamate receptor 4
keywords: Computational Biology; G Protein; G Protein-coupled Receptors; Metabotropic Glutamate Receptor (mGluR); Molecular Evolution; Signal Transduction