Dual function of the voltage-dependent Ca2+ channel alpha(2)delta subunit in current stimulation and subunit interaction

Voltage-dependent Ca2+ channels are modulated by complex interactions with the alpha(2) delta subunit. In vitro translation was used to demonstrate a single transmembrane topology of the alpha(2) delta subunit in which all but the transmembrane sequence and 5 carboxy-terminal amino acids are extracellular. The glycosylated extracellular domain is required for current stimulation, as shown by coexpression of truncated alpha(2) delta subunits with alpha(1A) and beta(4) subunits in Xenopus oocytes and deglycosylation with peptide-N-glycosidase F. However, coexpression of the transmembrane domain-containing delta subunit reduced the stimulatory effects of full-length alpha(2) delta subunits and substitution of a different transmembrane domain resulted in a loss of current stimulation. These results support a model whereby the alpha(2) delta transmembrane domain mediates subunit interactions and the glycosylated extracellular domain enhances current amplitude.