Direct inhibition of Ca2.3 by Gem is dynamin dependent and does not require a direct alfa/beta interaction.

The Rad, Rem, Rem2, and Gem/Kir (RGK) sub-family of small GTP-binding proteins are crucial in regulating high voltage-activated (HVA) calcium channels. RGK proteins inhibit calcium current by either promoting endocytosis or reducing channel activity. They all can associate directly with Ca channel β subunit (Caβ), and the binding between Caα1/Caβ appears essential for the endocytic promotion of Ca1.X, Ca2.1, and Ca2.2 channels. In this study, we investigated the inhibition of Ca2.3 channels by RGK proteins in the absence of Caβ. To this end, Xenopus laevis oocytes expressing Ca2.3 channels devoid of auxiliary subunit were injected with purified Gem and Rem and found that only Gem had an effect. Ca currents and charge movements were reduced by injection of Gem, pointing to a reduction in the number of channels in the plasma membrane. Since this reduction was ablated by co-expression of the dominant-negative mutant of dynamin K44A, enhanced endocytosis appears to mediate this reduction in the number of channels. Thus, Gem inhibition of Ca2.3 channels would be the only example of a Caβ independent promotion of dynamin-dependent endocytosis.