GRM1 and Huntington disease: SUMO proteomic pathways differentially enriched in HD included the proteins ARF1, PICK1, NMDZ1 and GRM5, all of which take part in glutamatergic signalling, either via AMPA receptor trafficking or direct activation by glutamate.72-74 Multiple mGLUR subtypes were identified within the SUMO proteomic dataset, including mGLUR1, 2, 3, 5 and 7.