Native high-voltage-gated calcium channels are multi-subunit complexes comprising a pore-forming subunit Cav and at least two auxiliary subunits α2δ and β. The β subunit facilitates cell-surface expression of the channel and contributes significantly to its biophysical properties. In spite of its importance, detailed structural and functional studies are hampered by the limited availability of native β subunit. Here, we report the purification of a recombinant calcium-channel β4 subunit from bacterial extracts by using a polyhistidine tag. The purified protein is fully functional since it binds on the alpha1 interaction domain, its main Cav-binding site, and regulates the activity of P/Q calcium channel expressed in Xenopus oocytes in a similar way to the β4 subunit produced by cRNA injection. We took advantage of the functionality of the purified material to (i) develop an efficient surface-plasmon resonance assay of the interaction between two calcium channel subunits and (ii) measure, for the first time, the affinity of the recombinant His-β4 subunit for the full-length Cav2.1 channel. The availability of this purified material and the development of a surface-plasmon resonance assay opens two immediate research perspectives: (i) drug screening programmes applied to the Cav/β interaction and (ii) crystallographic studies of the calcium-channel β4 subunit.
Abbreviations used: AID, alpha1 interaction domain; β4RNA, β4 expressed by cRNA injection; GST, glutathione S-transferase; MCAC, metal-chelate affinity chromatography; SPR, surface-plasmon resonance.