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

Abstract

The auxiliary α₂δ subunits of voltage-gated calcium channels are extracellular membrane-associated proteins, which are post-translationally cleaved into disulfide-linked polypeptides α₂ and δ. We now show, using α₂δ constructs containing artificial cleavage sites, that this processing is an essential step permitting voltage-dependent activation of plasma membrane N-type (Ca_V2.2) calcium channels. Indeed, uncleaved α2δ inhibits native calcium currents in mammalian neurons. By inducing acute cell-surface proteolytic cleavage of α₂δ, voltage-dependent activation of channels is promoted, independent from the trafficking role of α₂δ. Uncleaved α₂δ does not support trafficking of Ca_V2.2 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 α₂δ subunits maintain immature calcium channels in an inhibited state. Proteolytic processing of α₂δ then permits voltage-dependent activation of the channels, acting as a checkpoint allowing trafficking only of mature calcium channel complexes into neuronal processes.