Accessory protein required for glutamate-gated currents. May participate in the gating of non-NMDA (N-methyl-D-aspartate) ionotropic glutamate receptors such as glr-1. Interacts with glr-1. Colocalizes with glr-1 at the cell surface. Enriched at postsynaptic membranes. Widely expressed in the nervous system. Also expressed in neurons that do not express glr-1.