RT Journal Article SR Electronic T1 Covalent and Noncovalent Interactions Mediate Metabotropic Glutamate Receptor mGlu5 Dimerization JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 46 OP 53 DO 10.1124/mol.59.1.46 VO 59 IS 1 A1 Romano, Carmelo A1 Miller, Judith Kelvin A1 Hyrc, Krzysztof A1 Dikranian, Seta A1 Mennerick, Steven A1 Takeuchi, Yutaka A1 Goldberg, Mark P. A1 O'Malley, Karen L. YR 2001 UL http://molpharm.aspetjournals.org/content/59/1/46.abstract AB Some, perhaps all, G protein-coupled receptors form homo- or heterodimers. We have shown that metabotropic glutamate receptors are covalent dimers, held together by one or more disulfide bonds near the N terminus. Here we report how mutating cysteines in this region affect dimerization and function. Covalent dimerization is preserved when cysteines 57, 93, or 99 are mutated but lost with replacement at 129. Coimmunoprecipitation under nondenaturing conditions indicates that the C[129]S mutant receptor remains a dimer, via noncovalent interactions. Both C[93]S and C[129]S bind [3H]quisqualate, whereas binding to C[57]S or C[99]S mutants is absent or greatly attenuated. The C[93]S and C[129]S receptors have activity similar to wild-type when assayed by fura-2 imaging of intracellular calcium in human embryonic kidney cells or electrophysiologically in Xenopus laevis oocytes. In contrast, C[57]S or C[99]S are less active in both assays but do respond with higher glutamate concentrations in the oocyte assay. These results demonstrate that 1) covalent dimerization is not critical for mGlu5 binding or function; 2) mGlu5 remains a noncovalent dimer even in the absence of covalent dimerization; and 3) high-affinity binding requires Cys-57 and Cys-99.