The ligand-binding domain of the delta family of ionotropic glutamate receptors, a member of the type 2 periplasmic-binding fold protein superfamily.
This subfamily represents the ligand-binding domain of an orphan family of delta receptors, GluRdelta1 and GluRdelta2. While this ligand-binding domain is structurally homologous to the periplasmic-binding fold type II superfamily, the N-terminal domain of iGluRs belongs to the periplasmic-binding fold type I. Although the delta receptors are members of the ionotropic glutamate receptor family, they cannot be activated by AMPA, kainate, NMDA, glutamate, or any other ligands. Phylogenetical analysis shows that both GluRdelta1 and GluRalpha2 are more homologous to non-NMDA receptors. GluRdelta2 was shown to function as an AMPA-like receptor by mutation analysis. Moreover, targeted disruption of GluRdelta2 gene caused motor coordination impairment, Purkinje cell maturation, and long-term depression of synaptic transmission. It has been suggested that GluRdelta2 is the receptor for cerebellin 1, a glycoprotein of the Clq, and the tumor necrosis factor family which is secreted from cerebellar granule cells. Furthermore, recent studies have shown that the orphan GluRdelta1 plays an essential role in high-frequency hearing and ionic homeostasis in the basal cochlea and that the locus encoding GluRdelta1 may be involved in congenial or acquired high-frequency hearing loss in humans.
Jiyao W et al.(2023). "The conserved domain database in 2023.",