Synaptic neurotransmitter release is driven by Ca2+ influx through active zone voltage-gated calcium channels (VGCCs)1,2. Control of active zone VGCC abundance and function remains poorly understood. Here we show that a trafficking step probably sets synaptic VGCC levels in rats, because overexpression of the pore-forming α1A VGCC subunit fails to change synaptic VGCC abundance or function. α2δs are a family of glycosylphosphatidylinositol (GPI)-anchored VGCC-associated subunits3 that, in addition to being the target of the potent neuropathic analgesics gabapentin and pregabalin (α2δ-1 and α2δ-2)4,5, were also identified in a forward genetic screen for pain genes (α2δ-3)6. We show that these proteins confer powerful modulation of presynaptic function through two distinct molecular mechanisms. First, α2δ subunits set synaptic VGCC abundance, as predicted from their chaperone-like function when expressed in non-neuronal cells3,7. Second, α2δs configure synaptic VGCCs to drive exocytosis through an extracellular metal ion-dependent adhesion site (MIDAS), a conserved set of amino acids within the predicted von Willebrand A domain of α2δ. Expression of α2δ with an intact MIDAS motif leads to an 80% increase in release probability, while simultaneously protecting exocytosis from blockade by an intracellular Ca2+ chelator. α2δs harbouring MIDAS site mutations still drive synaptic accumulation of VGCCs; however, they no longer change release probability or sensitivity to intracellular Ca2+ chelators. Our data reveal dual functionality of these clinically important VGCC subunits, allowing synapses to make more efficient use of Ca2+ entry to drive neurotransmitter release.
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We thank W. Pratt for performing mutagenesis on α2δ-1 and M. D’Arco for advice on immunocytochemistry. We thank S. Kim for designing the vGmOr2 and VAMPmCh plasmids, P. Ariel for helpful discussion and analysis of exocytosis data, R. Kwan and Y. Gera for technical assistance in cell culture, G. Obermair for providing the wild-type EGFP–α1A plasmid and L. Looger for providing the GCaMP3 plasmid and helpful communication.
The authors declare no competing financial interests.
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Hoppa, M., Lana, B., Margas, W. et al. α2δ expression sets presynaptic calcium channel abundance and release probability. Nature 486, 122–125 (2012). https://doi.org/10.1038/nature11033
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