Channelpedia

cacng3

Description: calcium channel, voltage-dependent, gamma subunit 3
Gene: Cacng3     Synonyms: cacng3

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Introduction

The protein encoded by CACNG3 is a type I transmembrane AMPA receptor regulatory protein (TARP). 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 childhood absence epilepsy.

http://www.ncbi.nlm.nih.gov/gene/10368


Experimental data


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Gene

Phylogenetic analysis suggests that all c subunits evolved from a single ancestral gene through tandem repeat and chromosome duplication (Burgess [1312], chu [1311]). 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 [1311]). Interestingly, these clusters also mirror to some extent the tissue distribution of the subunits and their likely cellular functions. (Chen [1310])

RGD ID Chromosome Position Species
628803 1 181498716-181594090 Rat
732127 7 129815258-129912907 Mouse
736548 16 24266876-24373737 Human

Cacng3 : calcium channel, voltage-dependent, gamma subunit 3


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Transcript

Acc No Sequence Length Source
NM_080691 n/A n/A NCBI
NM_019430 n/A n/A NCBI
NM_006539 n/A n/A NCBI

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Ontology

Accession Name Definition Evidence
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
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

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Interaction

c2, c3 (=cacng3, the third gamma unit), c4, and c8 contain several common regulatory sites in both the extracellular and intracellular domains. The most distinct features of the TARPs are the terminal PDZ-binding motifs overlapped with PKA phosphorylation sites. The terminal TTPV motif is known to interact with PSD-95 in the postsynaptic density and the binding is regulated by the PKA motif immediately preceding the PDZ-binding motif (Chetkovich [1325], Choi [1326]). This combination determines the synaptic targeting of TARPs and AMPA receptors. In addition, the nPIST- binding motifs in the center portion of the C-terminal tail of TARPs regulates membrane-trafficking and synaptic targeting of the TARPs (Cuadra [1333]). A series of nine serine residues in the N-terminal portion of nPIST-binding motif are regulated by kinases (CAMKII, PKC) and phosphatases (PP2B and PP1). A tyrosine sulfation site also exists in the first extracellular loop of the TARPs. Tyrosine sulfation occurs when proteins travel through the Golgi lumen. This modification strengthens protein–protein interactions and is usually observed in proteins involved in intercellular interactions and communication. (Chen [1310])


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Protein


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Structure

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 [4], 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])


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Distribution


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Expression


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Functional

When over-expressed in heterologous systems 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]).


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Kinetics


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Model


References

Chen RS. et al. Calcium channel gamma subunits: a functionally diverse protein family.
Cell Biochem. Biophys., 2007 , 47 (178-86).

1332

Sander T. et al. Linkage and association analysis of CACNG3 in childhood absence epilepsy.
Eur. J. Hum. Genet., 2007 Apr , 15 (463-72).

1324

Campbell KP. et al. Auxiliary subunits: essential components of the voltage-gated calcium channel complex.
Curr. Opin. Neurobiol., 2003 Jun , 13 (298-307).

478

Black JL. et al. The voltage-gated calcium channel gamma subunits: a review of the literature.
J. Bioenerg. Biomembr., 2003 Dec , 35 (649-60).

Choi J. et al. Phosphorylation of stargazin by protein kinase A regulates its interaction with PSD-95.
J. Biol. Chem., 2002 Apr 5 , 277 (12359-63).

Hofmann F. et al. A family of gamma-like calcium channel subunits.
FEBS Lett., 2000 Mar 24 , 470 (189-97).

Mori Y. et al. The mouse stargazer gene encodes a neuronal Ca2+-channel gamma subunit.
Nat. Genet., 1998 Aug , 19 (340-7).


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Credits