Mutation of a glutamate receptor motif reveals its role in gating and δ2 receptor channel properties

Despite its importance in the cerebellum, the functions of the orphan glutamate receptor δ2 are unknown. We examined a mutant δ2 receptor channel in lurcher mice that was constitutively active in the absence of ligand. Because this mutation was within a highly conserved motif (YTANLAAF), we tested its effect on several glutamate receptors. Mutant δ2 receptors showed distinct channel properties, including double rectification of the current- voltage relationship, sensitivity to a polyamine antagonist and moderate Ca²⁺ permeability, whereas other constitutively active mutant glutamate channels resembled wildtype channels in these respects. Moreover, the kinetics of ligand-activated currents were strikingly altered. We conclude that the δ2 receptor has a functional ion channel pore similar to that of glutamate receptors. The motif may have a role in the channel gating of glutamate receptors.