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 CYTH3, GRM2, GRM3 and GRM5. Expressed in brain.