Rem2 belongs to the RGK family of small GTPases whose members are known to interact with the voltage gated calcium channel beta subunit, and to inhibit or abolish calcium currents. To identify the underlying functional domains of Rem2, we created several N- or C-terminally truncated Rem2 proteins and examined their abilities to interact with the Ca(v) beta subunit and to regulate the activities of Ca(v)2.2 N-type calcium channels. Confocal imaging of Rem2 in tsA-201 cells revealed that it contains a membrane-targeting signal in its C-terminus, consistent with previous studies. Co-precipitation assays showed that Ca(v) beta(3) interaction depends on Rem2 residues 1-123. Only Rem2 proteins that targeted the cell membrane as well as bound the beta subunit were able to reduce whole cell calcium currents.