Primary structure and functional expression of the AMPA/kainate receptor subunit 2 from human brain

A full-length cDNA clone encoding the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate (KA) receptor subunit 2 (HBGR2) was isolated from a human brain cDNA library. The HBGR2 cDNA has an open reading frame of approximately 2.7 kb that codes for an 883-residue protein. At the amino acid level, HBGR2 is 98% identical to its rat counterpart GluR2, and 69% to the AMPA/KA receptor subunit 1 from human brain (HBGR1). Injection of cRNA transcripts from the HBGR2 into oocytes produces barely detectable kainate-activated ionic currents, indicating that the HBGR2 subunit alone weakly expresses homomeric receptor channels. Coexpression of HBGR2 and HBGR1 transcripts, however, evokes kainate-dependent currents which activate at higher agonist concentration than those required by homomeric HBGR1 receptor channels. Coexpressed receptors display a linear current-to-voltage relationship at variance with the inwardly rectifying profile exhibited by HBGR1 homomers. Hence, the HBGR2 subunit coassembles with the HBGR1 subunit to form heteromeric receptor channels akin to the glutamate receptors from rodent brain.