Regulates the trafficking and gating properties of AMPA-selective glutamate receptors (AMPARs). Promotes their targeting to the cell membrane and synapses and modulates their gating properties by regulating their rates of activation, deactivation and desensitization. Blocks CACNG8-mediated resensitization of AMPA receptors. Acts as an auxiliary subunit for AMPA-selective glutamate receptors (AMPARs). Found in a complex with GRIA1, GRIA2, GRIA3, GRIA4, CNIH3, CACNG2, CACNG3, CACNG4, CACNG5, CACNG7 and CACNG8 (By similarity). Interacts with CACGN8 (By similarity). Interacts with GRIA1. Also localizes to the cell membrane of extrasynaptic sites (dendritic shafts, spines of pyramidal cells). Expression is up-regulated in dorsolateral prefrontal cortex of patients with schizophrenia (postmortem brain study). Belongs to the cornichon family.