A deletion in the second cytoplasmic loop of GluR3 produces a dominant negative mutant of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor.

ABSTRACT

We have characterized a GluR3 mutant (sGluR3) which has a 33-amino acid deletion in its second cytoplasmic loop (deficit from Tyr-715 to Gly-747 of GluR3-flop). Xenopus oocytes injected with cRNA transcribed from cDNA for this mutant did not respond to kainate and glutamate (each 100 microM) at a holding potential of -70 mV. In oocytes coinjected with cRNAs for this mutant and for normal alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor subunits, the current response to both kainate and glutamate was much weaker than that observed in oocytes injected with cRNA for the normal subunits alone. This inhibitory action was not accompanied by a significant change of ED50 value and shape of the I-V curve and was AMPA receptor-specific. A comparable deletion in GluR1 produced a mutant with properties similar to those of sGluR3, while a 33-amino acid deletion elsewhere in the second cytoplasmic loop of GluR3 (Met-674 to Phe-706) gave a mutant with a weaker effect. These results suggest that sGluR3 acts as a dominant negative mutant on the functional expression of normal AMPA receptors in oocytes by assembling with the normal subunits to produce an essentially nonfunctional receptor complex.