Cloning and deletion mutagenesis of the α2δ calcium channel subunit from porcine cerebral cortex -: Expression of a soluble form of the protein that retains [3H]gabapentin binding activity

The anti-epileptic, anti-hyperalgesic, and anxiolytic agent gabapentin (1-(aminomethyl)-cyclohexane acetic acid or Neurontin) has previously been shown to bind with high affinity to the alpha(2)delta subunit of voltage-dependent calcium channels (Gee, N. S., Brown, J. P., Dissanayake, V. U. K., Offord, J., Thurlow, R., and Woodruff, G.N. (1996) J. Biol. Chem. 271, 5768-5776). We report here the cloning, sequencing, and deletion mutagenesis of the alpha(2)delta subunit from porcine brain. The deduced protein sequence has a 95.9 and 98.2% identity to the rat and human neuronal alpha(2)delta sequences, respectively. [H-3]Gabapentin binds with a K-D of 37.5 +/- 10.4 nM to membranes prepared from COS-7 cells transfected with wild-type porcine alpha(2)delta cDNA. Six deletion mutants (B-G) that lack the delta polypeptide, together with varying amounts of the alpha(2) component, failed to bind [H-3]gabapentin. C-terminal deletion mutagenesis of the delta polypeptide identified a segment (residues 960-994) required for correct assembly of the [H-3]gabapentin binding pocket. Mutant L, which lacks the putative membrane anchor in the delta sequence, was found in both membrane-associated and soluble secreted forms. The soluble form was not proteolytically cleaved into separate alpha(2) and delta chains but still retained a high affinity (K-D = 30.7 +/- 8.1 nM) for [H-3]gabapentin. The production of a soluble alpha(2)delta mutant supports the single transmembrane model of the alpha(2)delta subunit and is an important step toward the large-scale recombinant expression of the protein.