Regulates the activity of L-type calcium channels that contain CACNA1C as pore-forming subunit (By similarity). 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 slowing their rates of activation, deactivation and desensitization and by mediating their resensitization. Does not show subunit-specific AMPA receptor regulation and regulates all AMPAR subunits. Interacts with CACNA1C. Identified in a complex with the L-type calcium channel subunits CACNA1C, CACNA2D1 and either CACNB1 or CACNB2. 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, CACNG5 and CACNG7. Interacts with CNIH2. Detected in heart left ventricle. Palmitoylated. Probably palmitoylated by ZDHHC3 and ZDHHC7. Belongs to the PMP-22/EMP/MP20 family. CACNG subfamily. Contaminating sequence. Sequence of unknown origin in the N-terminal part.