cacng2
Description: calcium channel, voltage-dependent, gamma subunit 2 Gene: Cacng2 Synonyms: cacng2
The second member of the calcium channel gamma subunit family, gamma2 (=CACNG2), was identified from genetic analysis of the stargazer mouse, an animal that displays a characteristic phenotype that includes head tossing and epileptic episodes (Noebels [1327]).
CACNG2 (also known as FLJ41437; MGC138502; MGC138504) encodes a type I transmembrane AMPA receptor regulatory protein (TARP), also known as a gamma2 subunit. TARPs regulate both trafficking and channel gating of the AMPA receptors. This gene is part of a functionally diverse eight-member protein subfamily of the PMP-22/EMP/MP20 family. This gene is a susceptibility locus for schizophrenia.
http://www.ncbi.nlm.nih.gov/gene/10369
Gene
Phylogenetic analysis suggests that all c subunits evolved from a single ancestral gene through tandem repeat and chromosome duplication (Burgess [1312], Chu [1312]). Based on sequence homology and chromosomal linkage the c subunits can be divided into three clusters: (c1, c6), (c5, c7), and (c2, c3, c4, c8) (Burgess [1312], Chu [1312]).
Transcript
Ontology
Accession | Name | Definition | Evidence | |||||||
---|---|---|---|---|---|---|---|---|---|---|
GO:0016020 | membrane | Double layer of lipid molecules that encloses all cells, and, in eukaryotes, many organelles; may be a single or double lipid bilayer; also includes associated proteins. | IEA | |||||||
GO:0016021 | integral to membrane | Penetrating at least one phospholipid bilayer of a membrane. May also refer to the state of being buried in the bilayer with no exposure outside the bilayer. When used to describe a protein, indicates that all or part of the peptide sequence is embedded in the membrane. | IEA |
Interaction
In addition to the critical PDZ-binding motif, the C-terminal regions of the four gamma (c) subunits known as the TARPs (c2, c3, c4, c8) also contain regulatory sites that control AMPA receptor targeting. For instance, the second threonine in the PDZ-binding motif (TTPV) of c2 (=cacng2) is a consensus site for phosphorylation by PKA, PKC, PKG, and CaMKII suggesting that phosphorylation may regulate the interaction between c2 and the AMPA receptor. Indeed, two groups have independently found that phosphorylation by PKA interfered with the binding between c2 and PSD-95 (Chetkovich [1325], Choi [1326]). Consequently, reduced synaptic targeting of c2 prevents its interaction with the AMPA receptor, resulting in weakened synaptic efficiency (Choi [1326]).
Protein
The eight calcium channel c subunits share a predicted structure that includes four transmembrane domains with intracellular N- and C- termini (Fig. 1 in Chen [1310]). They are members of a large protein superfamily (pfam00822, a subset of the tetraspanin supergroup) that also includes claudins, proteins that are important components of tight junctions in epithelia. The c subunits share with the claudins a conserved GLW motif of unknown significance in the first extracellular loop. (Chen [1310])
The four c subunits identified as regulators of AMPA receptor function (c2, c3, c4, and c8; the TARPs) are widely expressed in the brain and share highly conserved sequences that are quite distinct from c1 and c6 (Arikkath [1324], Black [478]). Notably, the cytoplasmic C-terminal regions of the TARPs contain a number of regulatory sites including a PDZ-binding motif. This PDZ-binding motif (TTPV) is critical for targeting AMPA receptors to the synapse. (Chen [1310])
Distribution
Expression
Functional
c2, c3, and c4 are reported to hyperpolarize the voltage-dependence of inactivation of Cav2.1 (HVA) current by 3–7 mV (Klugbauer [1328], Letts [1329], Rousset [1330]). However, the direction of this shift is apparently altered when a b subunit is co-expressed (Rousset [1330]). Two studies have reported small (3–5 mV) shifts in the voltage- dependence of activation by c2 but in different directions (Klugbauer [1328], Rousset [1330]). The only reported effect of c2, c3, and c4 on Cav3.3 (LVA) current is that c2 slows the deactivation rate of Cav3.3 channel (Green [240]). Unlike the results with c1 and c6, significant decreases in current amplitude were not rou- tinely found with any of the TARPs, although modulation of Cav2 current amplitude has been reported (Kang [239]). Currently, there is no evidence supporting an effect of these subunits on calcium currents in native cells. Specifically, there are no observable changes in calcium currents recorded from cerebellar granule neurons in the stargazer mouse in which the c2 gene is mutated (Chen [1331]).
Kinetics
Model
References
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Susceptibility to chronic pain following nerve injury is genetically affected by CACNG2.
Genome Res.,
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Calcium channel gamma subunits: a functionally diverse protein family.
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Chu PJ
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Calcium channel gamma subunits provide insights into the evolution of this gene family.
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Burgess DL
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A cluster of three novel Ca2+ channel gamma subunit genes on chromosome 19q13.4: evolution and expression profile of the gamma subunit gene family.
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Arikkath J
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Auxiliary subunits: essential components of the voltage-gated calcium channel complex.
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Black JL
The voltage-gated calcium channel gamma subunits: a review of the literature.
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2003
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Chetkovich DM
et al.
Phosphorylation of the postsynaptic density-95 (PSD-95)/discs large/zona occludens-1 binding site of stargazin regulates binding to PSD-95 and synaptic targeting of AMPA receptors.
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Phosphorylation of stargazin by protein kinase A regulates its interaction with PSD-95.
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Noebels JL
et al.
Stargazer: a new neurological mutant on chromosome 15 in the mouse with prolonged cortical seizures.
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1990
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Klugbauer N
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A family of gamma-like calcium channel subunits.
FEBS Lett.,
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Letts VA
et al.
The mouse stargazer gene encodes a neuronal Ca2+-channel gamma subunit.
Nat. Genet.,
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Rousset M
et al.
Functional roles of gamma2, gamma3 and gamma4, three new Ca2+ channel subunits, in P/Q-type Ca2+ channel expressed in Xenopus oocytes.
J. Physiol. (Lond.),
2001
May
1
, 532 (583-93).
Green PJ
et al.
Kinetic modification of the alpha(1I) subunit-mediated T-type Ca(2+) channel by a human neuronal Ca(2+) channel gamma subunit.
J. Physiol. (Lond.),
2001
Jun
1
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Kang MG
et al.
Biochemical and biophysical evidence for gamma 2 subunit association with neuronal voltage-activated Ca2+ channels.
J. Biol. Chem.,
2001
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31
, 276 (32917-24).
Chen L
et al.
Stargazin regulates synaptic targeting of AMPA receptors by two distinct mechanisms.
Nature,
2000 Dec 21-28
, 408 (936-43).
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