Probing the Homo- and Hetero-Dimerization Propensities of Metabotropic Glutamate Receptors

Abstract

The metabotropic glutamate receptors (mGluR) are class C G-protein coupled receptors (GPCR) which play important roles in modulating excitatory and inhibitory synaptic transmission. mGluRs function as dimers which are covalently linked through an intersubunit disulfide bond located in the ligand binding domain. In recent years it has become clear that some mGluR combinations can form hetero-dimers with distinct functional properties. However, little is known about the relative propensities for homo- versus hetero-dimerization and the mechanisms that regulate specific mGluR assembly. Here, we develop a quantitative, fluorescence-based complementation assay to study dimerization of mGluRs in living cells. We find a range of dimerization propensities, including many cases of preferential hetero-dimerization compared to homo-dimerization. Single molecule pulldown of full-length mGluR2 confirms the relative propensities which includes a strong preference for mGluR2/3 heterodimerization, which we further validate with native proteins. Finally, using a combination of structural and computational analysis in conjunction with fluorescence-based studies we probe the role of relative conformational dynamics and inter-subunit interface complementarity in determining dimerization specificity. Overall, our findings support the biological relevance of mGluR heterodimerization and motivate a thorough analysis of the physiological roles of different dimer combinations.