Proteolytic maturation of α2δ represents a checkpoint for activation and neuronal trafficking of latent calcium channels

The auxiliary alpha(2)delta subunits of voltage-gated calcium channels are extracellular membrane-associated proteins, which are post-translationally cleaved into disulfide-linked polypeptides alpha(2) and delta. We now show, using alpha(2)delta constructs containing artificial cleavage sites, that this processing is an essential step permitting voltage-dependent activation of plasma membrane N-type (Ca(V)2.2) calcium channels. Indeed, uncleaved alpha(2)delta inhibits native calcium currents in mammalian neurons. By inducing acute cell-surface proteolytic cleavage of alpha(2)delta, voltage-dependent activation of channels is promoted, independent from the trafficking role of alpha(2)delta. Uncleaved alpha(2)delta does not support trafficking of CaV2.2 channel complexes into neuronal processes, and inhibits Ca2+ entry into synaptic boutons, and we can reverse this by controlled intracellular proteolytic cleavage. We propose a model whereby uncleaved alpha(2)delta subunits maintain immature calcium channels in an inhibited state. Proteolytic processing of alpha(2)delta then permits voltage-dependent activation of the channels, acting as a checkpoint allowing trafficking only of mature calcium channel complexes into neuronal processes.