The novel product of a five-exon stargazin-related gene abolishes CaV2.2 calcium channel expression

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Abstract
We have cloned and characterized a new member of the voltage‐dependent Ca2+ channel γ subunit family, with a novel gene structure and striking properties. Unlike the genes of other potential γ subunits identified by their homology to the stargazin gene, CACNG7 is a five‐, and not four‐exon gene whose mRNA encodes a protein we have designated γ7. Expression of human γ7 has been localized specifically to brain. N‐type current through CaV2.2 channels was almost abolished when co‐expressed transiently with γ7 in either Xenopus oocytes or COS‐7 cells. Furthermore, immunocytochemistry and western blots show that γ7 has this effect by causing a large reduction in expression of CaV2.2 rather than by interfering with trafficking or biophysical properties of the channel. No effect of transiently expressed γ7 was observed on pre‐existing endogenous N‐type calcium channels in sympathetic neurones. Low homology to the stargazin‐like γ subunits, different gene structure and the unique functional properties of γ7 imply that it represents a distinct subdivision of the family of proteins identified by their structural and sequence homology to stargazin.