Plays a role in intracellular trafficking and contributes to the macromolecular organization of group 1 metabotropic glutamate receptors (mGluRs) at synapses. Heteromer. Composed of TAMALIN, CYTH2 and at least one GRM1. Also interacts with GRM2, GRM3 and GRM5 (By similarity). Interacts with CYTH3 (PubMed:10828067). Highly expressed in brain, heart and lung, and to a lower extent in embryo, kidney and ovary.