Regulates the gating properties of AMPA-selective glutamate receptors (AMPARs). Modulates their gating properties by accelerating their rates of activation, deactivation and desensitization. Displays subunit-specific AMPA receptor regulation. Shows specificity for GRIA1, GRIA4 and the long isoform of GRIA2. According to PubMed:18817736, shows only specificity for GRIA2 and specifically to the form of GRIA2 for which a single amino acid in the pore region has been edited from a glutamine to an arginine residue. Thought to stabilize the calcium channel in an inactivated (closed) state. The L-type calcium channel is composed of five subunits: alpha-1, alpha-2/delta, beta and gamma. Acts as an auxiliary subunit for AMPA-selective glutamate receptors (AMPARs). Found in a complex with GRIA1, GRIA2, GRIA3, GRIA4, CNIH2, CNIH3, CACNG2, CACNG3, CACNG4, CACNG7 and CACNG8. Interacts with GRIA1, GRIA2, GRIA3 and GRIA4. Belongs to the PMP-22/EMP/MP20 family. CACNG subfamily.