Metabotropic glutamate receptors (mGluRs) belong to the super family of G-protein coupled receptors (seven transmembrane proteins). mGluRs are further divided into subfamilies: group I mGluRs (mGluR1 and mGluR5) which couple to Gq, thereby activating phospholipase C (PLC). Group II which include mGluR2 and mGluR3 couple to Gi, therefore inhibit the formation of adenylate cyclase. mGluR4, 6, 7, 8 which belong to group III also inhibit adenylate cyclase formation by coupling to Gi1.
The C-terminus of these receptors has important functions in modulating their activity. This region is important for G-protein coupling, post-translational modifications like phosphorylation as well as protein-protein interactions. The C-terminal region is also subject to alternative splicing2.
mGluR4 is predominantly expressed presynaptically in neurons and in the cerebellum. A splice variant of the protein is expressed in taste buds. This variant lacks a large portion of the N-terminus and is normally referred to taste mGluR43,4. It is responsible (along with taste mGluR1) for mediating the taste of monosodium glutamate (or unami)2,4.
mGluR4 knock out mice display impaired cerebellar synaptic plasticity as well as some learning disabilities5. In addition, this receptor has emerged as a target for the treatment of Parkinson
