Metabotropic glutamate receptors (mGluR) are Class C GPCRs. They are obligate dimers, dimerization being fundamental for their function. mGluRs are activated by the binding of the main excitatory neurotransmitter glutamate, within an extracellular domain (ECD). Conformational changes induced by glutamate-binding are then transmitted to the transmembrane domain composed of 7 transmembrane helices (7TM) that allows signal transduction within the cell. Class C GPCR activity can be modulated by the binding of Positive Allosteric Modulators (PAM) or Negative Allosteric Modulators (NAM) to the 7TM. Our research interest is to understand the structural basis of class C GPCR dimers signal transduction and their allosteric regulation. Multiple structures of PAM bound receptor will be solved and they will provide a comprehensive understanding on the nature of ligand binding in the 7TM as well as conformational changes associated to the binding of PAM at the mGlu receptor.