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calcium channel, voltage-dependent, gamma subunit 7
The protein encoded by CACNG7 is a type II 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 and is located in a cluster with two family members, a type I TARP and a calcium channel gamma subunit. http://www.ncbi.nlm.nih.gov/gene/59284
Phylogenetic analysis suggests that all c subunits evolved from a single ancestral gene through tandem repeat and chromosome duplication (Burgesse , Chu ). 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) (Burgesse , Chu ). See also the phylogenetic tree, fig.2 in Black .
c5 and c7 are encoded by five exons in contrast to all other c subunits, which are encoded by four exons (Moss , Chu ). A protein originally identified as mouse c5 (Klugbauer ) is currently named transmembrane protein 37 (Tmem37, NCBI database). Although Tmem37 is also a tetraspanin protein with the GLW motif characteristic of the pfam0082 protein family, its gene consists of only two exons, indicating a divergence from other c subunit genes during evolution. Based on phylogenetic evidence, Chu et al. proposed that Tmem37 should not be considered a member of the calcium channel c family (Chu ). This conclusion is further supported by the observation that Tmem37 does not share the chromosomal linkage to c4 and c1 in human (Burgess ), mouse and rat (Chu ) that is seen for c5 (Table 2 in Chen ).
Cacng7 : calcium channel, voltage-dependent, gamma subunit 7
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 ). 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 
c5, c7: c5, and c7 are palmitoylated at both the N- and C- termini. Additionally, their C-terminal tails contain tyrosine phosphorylation sites. Chen 
c7 subunit dramatically reduced current density produced by the Cav2.2 subunit in Xenopus oocytes and COS-7 cells (Moss ). However, when expressed in sympathetic neurons c7 failed to affect pre-existing HVA Ca2+ channels. Therefore, confirmation of the physiological influence of c7 on calcium current remains elusive. (Chen )
γ7, which is homologous to γ5, regulates stability of certain mRNAs (Ferron ) and, along with γ2 and γ8, controls trafficking and gating of AMPA receptors (Tomita , Kato ). It thus may be involved in ischemic cardiomyopathy (Gronich ).