Autism-associated mutations in the CaVβ2 calcium-channel subunit increase Ba2+-currents and lead to differential modulation by the RGK-protein Gem.

Voltage-gated calcium-channels (VGCCs) are heteromers consisting of several subunits. Mutations in the genes coding for VGCC subunits have been reported to be associated with autism spectrum disorder (ASD). In a previous study, we identified electrophysiologically relevant missense mutations of CaVβ2 subunits of VGCCs. From this, we derived the hypothesis that several CaVβ2-mutations associated with ASD show common features sensitizing LTCCs and/or enhancing currents. Using a CaVβ2d backbone, we performed extensive whole-cell and single-channel patch-clamp analyses of Ba2+ currents carried by Cav1.2 pore subunits co-transfected with the previously described CaVβ2 mutations (G167S, S197F) as well as a recently identified point mutation (V2D). Furthermore, the interaction of the mutated CaVβ2d subunits with the RGK protein Gem was analyzed by co-immunoprecipitation assays and electrophysiological studies. Patch-clamp analyses revealed that all mutations increase Ba2+ currents, e.g. by decreasing inactivation or increasing fraction of active sweeps. All CaVβ2 mutations interact with Gem, but differ in the extent and characteristics of modulation by this RGK protein (e.g. decrease of fraction of active sweeps: CaVβ2d_G167S > CaVβ2d_V2D > CaVβ2d_S197F). In conclusion, patch-clamp recordings of ASD-associated CaVβ2d mutations revealed differential modulation of Ba2+ currents carried by CaV1.2 suggesting kind of an "electrophysiological fingerprint" each. The increase in current finally observed with all CaVβ2d mutations analyzed might contribute to the complex pathophysiology of ASD and by this indicate a possible underlying molecular mechanism.