Calcium channel gamma subunits: a functionally diverse protein family.

The calcium channel gamma subunits comprise an eight-member protein family that share a common topology consisting of four transmembrane domains and intracellular N- and C-termini. Although the first gamma subunit was identified as an auxiliary subunit of a voltage-dependent calcium channel, a review of phylogenetic, bioinformatic, and functional studies indicates that they are a functionally diverse protein family. A cluster containing gamma1 and gamma6 conforms to the original description of the protein family as they seem to act primarily as subunits of calcium channels expressed in muscle. Members of a second cluster (gamma2, gamma3, gamma4, gamma8) function as regulators of AMPA receptor localization and function in the brain and are collectively known as TARPs. The function of members of the third cluster (gamma5, gamma7) remains unclear. Our analysis shows that the members of each cluster contain conserved regulatory motifs that help to differentiate the groups. However, the physiological significance of these motifs in many cases remains to be demonstrated.