G-protein-coupled receptors (GPCRs) can form heteromeric complexes. Herein, we describe a new approach to test the heteromerization of 2 receptors, or 2 receptor subunits, and to study the stoichiometry of the resulting complexes. As a proof-of-concept study, we investigated whether metabotropic glutamate receptors (mGluRs), in addition to being well-known homodimers, can form heteromers. To that aim, we combine the benefits of time-resolved fluorescence resonance energy transfer (trFRET) with the specific, cell-surface labeling of SNAP- and CLIP-tagged rat mGluR subunits, expressed in a mammalian cell line. First, we show that mGlu2 and mGlu4 subunits (but not mGlu2 and mGlu1) can heteromerize. Moreover, our trFRET data are consistent with mGluR subunits forming strict homodimeric receptors on single expression, and a combination of strict heterodimeric and strict homodimeric receptors on coexpression. Second, a comprehensive analysis reveals that from the 21 possible pairs of 2 mGluR subunits out of 7 subtypes (mGlu1 to 8, but not 6), only 11 are able to form heterodimers. These findings were further validated by biochemical and functional complementation studies. In addition to describing a new method to analyze cell-surface receptor complexes, our data reveal a new level of complexity within the mGluR family.

Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Abstract: A covalently functionalized fullerene comprising an electron donating aniline group coupled to the fullerene unit by a saturated heterocyclic bridge is shown to undergo a photoinduced intramolecular electron transfer process that causes quenching of the fluorescence of the adduct and strong decrease of triplet population in polar solvents. VIS-absorption, fluorescence and phosphorescence at 77 K, triplet-triplet absorption, time resolved fluorescence, and redox potentials of the fullerene adduct are presented. Analysis of the solvent dependence of the energetics of the intramolecular electron transfer is given and is in good agreement with the experimental results.

In multimeric cell-surface receptors, the conformational changes of the extracellular ligand-binding domains (ECDs) associated with receptor activation remain largely unknown. This is the case for the dimeric metabotropic glutamate receptors even though a number of ECD structures have been solved. Here, using an innovative approach based on cell-surface labeling and FRET, we demonstrate that a reorientation of the ECDs is associated with receptor and G-protein activation. Our approach helps identify partial agonists and highlights allosteric interactions between the effector and binding domains. Any approach expected to stabilize the active conformation of the effector domain increased the agonist potency in stabilizing the active ECDs conformation. These data provide key information on the structural dynamics and drug action at metabotropic glutamate receptors and validate an approach for tackling such analysis on other receptors.M any cell-surface receptors are multimers of proteins composed of several domains (1-3), including extracellular domains (ECDs) involved in endogenous ligand recognition and transmembrane domains (TMDs) responsible for intracellular signal transduction. Analysis of the conformational changes of the ECDs associated with receptor activation is crucial to understand the detailed mechanism involved in receptor activation and for the development of new innovative drugs. However, limited information is available on how the conformational changes in these proteins lead to receptor activation, especially in living cells.The eight glutamate-activated G-protein-coupled receptors (GPCRs), called "metabotropic glutamate receptors" (mGluRs), are key examples of multidomain and multimeric receptors (Fig. 1A). These receptors are strict dimers (4-6), and each subunit is made of a large ECD associated with a seven-helix TMD responsible for G-protein activation and downstream signaling (7). The mGluRs are key elements involved in the regulation of synaptic activity (8), and therefore they represent promising targets in drug development for the treatment of multiple neurologic and psychiatric diseases (9). More generally, the mGluRs are part of the class C GPCR family that contains structurally related receptors such as the receptors for sweet and umami taste, calcium, basic amino acids, and the inhibitory neurotransmitter GABA (10, 11).Crystallographic studies of the isolated dimeric ECDs and mutagenesis analyses have provided a clear view of the structure of the dimeric ECD and of the initial steps of mGluR activation. The ECD is composed of a Venus flytrap (VFT) bilobate domain containing the agonist binding site (12-15) and a cysteine-rich domain (CRD) that connects the VFT to the TMD (16). The VFTs exist in two major states: an open state (o) in absence of ligand and stabilized by antagonists, and a closed state (c) stabilized by agonists and required for receptor activation (12-15). The VFT dimer is in equilibrium between various conformations, depending on whether one or two VFTs are open or cl...

The synthesis, structure and photophysical properties of a series of highly emissive europium complexes is reported. Certain complexes enter mammalian cells by

G-protein-coupled receptors (GPCRs) are crucial cell surface receptors that transmit signals from a wide range of extracellular ligands. Indeed, 40% to 50% of all marketed drugs are thought to modulate GPCR activity, making them the major class of targets in the drug discovery process. Binding assays are widely used to identify high-affinity, selective, and potent GPCR drugs. In this field, the use of radiolabeled ligands has remained so far the gold-standard method. Here the authors report a less hazardous alternative for high-throughput screening (HTS) applications by the setup of a nonradioactive fluorescencebased technology named Tag