Faculty Opinions recommendation of Expression of Rem2, an RGK family small GTPase, reduces N-type calcium current without affecting channel surface density.

Rad, Gem/Kir, Rem, and Rem2 are members of the Ras-related RGK (Rad, Gem, and Kir) family of small GTP-binding proteins.Heterologous expression of RGK proteins interferes with de novo calcium channel assembly/trafficking and dramatically decreases the amplitude of currents arising from preexisting high-voltage-activated calcium channels.These effects probably result from the direct interaction of RGK proteins with calcium channel ␤ subunits.Among the RGK family, Rem2 is the only member abundantly expressed in neuronal tissues.Here, we examined the ability of Rem2 to modulate endogenous voltage-activated calcium channels in rat sympathetic and dorsal root ganglion neurons.Heterologous expression of Rem2 nearly abolished calcium currents arising from preexisting highvoltage-activated calcium channels without affecting low-voltage-activated calcium channels.Rem2 inhibition of N-type calcium channels required both the Ras homology (core) domain and the polybasic C terminus.Mutation of a putative GTP/Mg 2ϩ binding motif in Rem2 did not affect suppression of calcium currents.Loading neurons with GDP-␤-S via the patch pipette did not reverse Rem2-mediated calcium channel inhibition.Finally, [ 125 I]Tyr 22 --conotoxin GVIA cell surface binding in tsA201 cells stably expressing N-type calcium channels was not altered by Rem2 expression at a time when calcium current was totally abolished.Together, our results support a model in which Rem2 localizes to the plasma membrane via a C-terminal polybasic motif and interacts with calcium channel ␤ subunits in the preassembled N-type channel, thereby forming a nonconducting species.