Autism-associated mutations in the Ca_Vβ₂ 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 Ca_Vβ₂ subunits of VGCCs. From this, we derived the hypothesis that several Ca_Vβ₂-mutations associated with ASD show common features sensitizing LTCCs and/or enhancing currents. Using a Ca_Vβ_2d backbone, we performed extensive whole-cell and single-channel patch-clamp analyses of Ba²⁺ currents carried by Ca_v1.2 pore subunits co-transfected with the previously described Ca_Vβ₂ mutations (G167S, S197F) as well as a recently identified point mutation (V2D). Furthermore, the interaction of the mutated Ca_Vβ_2d 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 Ca_Vβ₂ 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: Ca_Vβ_{2d_G167S} > Ca_Vβ_{2d_V2D} > Ca_Vβ_{2d_S197F}). In conclusion, patch-clamp recordings of ASD-associated Ca_Vβ_2d mutations revealed differential modulation of Ba²⁺ currents carried by Ca_V1.2 suggesting kind of an "electrophysiological fingerprint" each. The increase in current finally observed with all Ca_Vβ_2d mutations analyzed might contribute to the complex pathophysiology of ASD and by this indicate a possible underlying molecular mechanism.

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