RGK GTPase-dependent CaV2.1 Ca²⁺ channel inhibition is independent of CaVβ-subunit-induced current potentiation

RGK (Rad-Gem-Rem) GTPases have been described as potent negative regulators of the Ca²⁺ influx via high-threshold voltage-activated Ca²⁺ channels. Recent work, mostly performed on CaV1.2 Ca²⁺ channels, has highlighted the crucial role played by the channel auxiliary CaVβ subunits and identified several GTPase and β-subunit protein domains involved in this regulation. We now extend these conclusions by producing the first complete characterization of the effects of Gem, Rem, and Rem2 on the neuronal CaV2.1 Ca²⁺ channels expressed with CaVβ₁ or CaVβ₂ subunits. Current inhibition is limited to a decrease in amplitude with no modification in the voltage dependence or kinetics of the current. We demonstrate that this inhibition can occur for CaVβ constructs with impaired capacity to induce current potentiation, but that it is lost for CaVβ constructs deleted for their β-interaction domain. The RGK C-terminal last ~80 amino acids are sufficient to allow potent current inhibition and in vivo β-subunit/Gem interaction. Interestingly, although Gem and Gem carboxy-terminus induce a completely different pattern of β-subunit cellular localization, they both potently inhibit CaV2.1 channels. These data therefore set the status of neuronal CaV2.1 Ca²⁺ channel inhibition by RGK GTPases, emphasizing the role of short amino acid sequences of both proteins in β-subunit binding and channel inhibition and revealing a new mechanism for channel inhibition.--Leyris, J.-P., Gondeau, C., Charnet, A., Delattre, C., Rousset, M., Cens, T., Charnet, P. RGK GTPase-dependent CaV2.1 Ca²⁺ channel inhibition is independent of CaVβ-subunit-induced current potentiation.