Proteolytic maturation of αδ represents a checkpoint for activation and neuronal trafficking of latent calcium channels.

The auxiliary αδ subunits of voltage-gated calcium channels are extracellular membrane-associated proteins, which are post-translationally cleaved into disulfide-linked polypeptides α and δ. We now show, using αδ constructs containing artificial cleavage sites, that this processing is an essential step permitting voltage-dependent activation of plasma membrane N-type (Ca2.2) calcium channels. Indeed, uncleaved α2δ inhibits native calcium currents in mammalian neurons. By inducing acute cell-surface proteolytic cleavage of αδ, voltage-dependent activation of channels is promoted, independent from the trafficking role of αδ. Uncleaved αδ does not support trafficking of Ca2.2 channel complexes into neuronal processes, and inhibits Ca entry into synaptic boutons, and we can reverse this by controlled intracellular proteolytic cleavage. We propose a model whereby uncleaved αδ subunits maintain immature calcium channels in an inhibited state. Proteolytic processing of αδ then permits voltage-dependent activation of the channels, acting as a checkpoint allowing trafficking only of mature calcium channel complexes into neuronal processes.