Glutamate receptor, ionotropic, delta 2, also known as GluD2, GluRδ2, or δ2, is a protein that in humans is encoded by the GRID2gene.[5][6] This protein together with GluD1 belongs to the delta receptor subtype of ionotropic glutamate receptors. They possess 14–24% sequencehomology with AMPA, kainate, and NMDA subunits, but, despite their name, do not actually bind glutamate or various other glutamate agonists.[7]
delta iGluRs have long been considered orphan receptors as their endogenousligand was unknown. They are now believed to bind glycine and D-serine but these do not result in channel opening.[8][9]
GluD2 induces synaptogenesis through interaction of its N-terminal domain with Cbln1, which in turn interacts with presynaptic neurexins, forming a bridge across cerebellar synapses.[11][12]
The main functions of GluD2 in synaptic plasticity are carried out by its intracellular C-terminus.[13] This is regulated by D-serine,[14] which binds to the ligand-binding domain and results in changes in the structure of GluD2 without opening the channel in the absence of pre-synaptic connections.[9] Glycine and D-serine can open the channel in GluD2 when bound to cerebellin-1 and neurexin-1β.[15] These changes may signal up to the N-terminal domain or down to the C-terminal domain to alter protein-protein interactions.
Pathology
A heterozygous deletion in GRID2 in humans causes a complicated spastic paraplegia with ataxia, frontotemporal dementia, and lower motor neuron involvement[16] whereas a homozygous biallelic deletion leads to a syndrome of cerebellar ataxia with marked developmental delay, pyramidal tract involvement[17] and tonic upgaze,[18] that can be classified as an ataxia with oculomotor apraxia (AOA) and has been named spinocerebellar ataxia, autosomal recessive type 18 (SCAR18).
A gain of channel function, resulting from a point mutation in mouse GRID2, is associated with the phenotype named 'lurcher', which in the heterozygous state leads to ataxia and motor coordination deficits resulting from selective, cell-autonomous apoptosis of cerebellar Purkinje cells during postnatal development.[19][20] Mice homozygous for this mutation die shortly after birth from massive loss of mid- and hindbrain neurons during late embryogenesis.
^Araki K, Meguro H, Kushiya E, Takayama C, Inoue Y, Mishina M (Dec 1993). "Selective expression of the glutamate receptor channel delta 2 subunit in cerebellar Purkinje cells". Biochemical and Biophysical Research Communications. 197 (3): 1267–76. doi:10.1006/bbrc.1993.2614. PMID7506541.
^Matsuda K, Yuzaki M (Mar 2012). "Cbln1 and the δ2 glutamate receptor--an orphan ligand and an orphan receptor find their partners". Cerebellum. 11 (1): 78–84. doi:10.1007/s12311-010-0186-5. PMID20535596. S2CID16612844.
^Maier A, Klopocki E, Horn D, Tzschach A, Holm T, Meyer R, Meyer T (Feb 2014). "De novo partial deletion in GRID2 presenting with complicated spastic paraplegia". Muscle & Nerve. 49 (2): 289–92. doi:10.1002/mus.24096. PMID24122788. S2CID26359325.
^Utine GE, Haliloğlu G, Salanci B, Çetinkaya A, Kiper PÖ, Alanay Y, Aktas D, Boduroğlu K, Alikaşifoğlu M (Jul 2013). "A homozygous deletion in GRID2 causes a human phenotype with cerebellar ataxia and atrophy". Journal of Child Neurology. 28 (7): 926–32. doi:10.1177/0883073813484967. PMID23611888. S2CID206550612.
^Williams K, Dattilo M, Sabado TN, Kashiwagi K, Igarashi K (May 2003). "Pharmacology of delta2 glutamate receptors: effects of pentamidine and protons". The Journal of Pharmacology and Experimental Therapeutics. 305 (2): 740–8. doi:10.1124/jpet.102.045799. PMID12606689. S2CID83540259.
Araki K, Meguro H, Kushiya E, Takayama C, Inoue Y, Mishina M (Dec 1993). "Selective expression of the glutamate receptor channel delta 2 subunit in cerebellar Purkinje cells". Biochemical and Biophysical Research Communications. 197 (3): 1267–76. doi:10.1006/bbrc.1993.2614. PMID7506541.
Hu W, Zuo J, De Jager PL, Heintz N (Jan 1998). "The human glutamate receptor delta 2 gene (GRID2) maps to chromosome 4q22". Genomics. 47 (1): 143–5. doi:10.1006/geno.1997.5108. PMID9465309.
Kohda K, Kamiya Y, Matsuda S, Kato K, Umemori H, Yuzaki M (Jan 2003). "Heteromer formation of delta2 glutamate receptors with AMPA or kainate receptors". Brain Research. Molecular Brain Research. 110 (1): 27–37. doi:10.1016/S0169-328X(02)00561-2. PMID12573530.
Yap CC, Muto Y, Kishida H, Hashikawa T, Yano R (Feb 2003). "PKC regulates the delta2 glutamate receptor interaction with S-SCAM/MAGI-2 protein". Biochemical and Biophysical Research Communications. 301 (4): 1122–8. doi:10.1016/S0006-291X(03)00070-6. PMID12589829.
Sonoda T, Mochizuki C, Yamashita T, Watanabe-Kaneko K, Miyagi Y, Shigeri Y, Yazama F, Okuda K, Kawamoto S (Nov 2006). "Binding of glutamate receptor delta2 to its scaffold protein, Delphilin, is regulated by PKA". Biochemical and Biophysical Research Communications. 350 (3): 748–52. doi:10.1016/j.bbrc.2006.09.109. PMID17027646.