Cloning and deletion mutagenesis of the alpha2 delta 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 alpha2delta 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 alpha2delta subunit from porcine brain. The deduced protein sequence has a 95.9 and 98.2% identity to the rat and human neuronal alpha2 delta sequences, respectively. [3H]Gabapentin binds with a KD of 37.5 +/- 10.4 nM to membranes prepared from COS-7 cells transfected with wild-type porcine alpha2 delta cDNA. Six deletion mutants (B-G) that lack the delta polypeptide, together with varying amounts of the alpha2 component, failed to bind [3H]gabapentin. C-terminal deletion mutagenesis of the delta polypeptide identified a segment (residues 960-994) required for correct assembly of the [3H]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 alpha2 and delta chains but still retained a high affinity (KD = 30.7 +/- 8.1 nM) for [3H]gabapentin. The production of a soluble alpha2delta mutant supports the single transmembrane model of the alpha2 delta subunit and is an important step toward the large-scale recombinant expression of the protein.
Brown
J P
JP
Parke-Davis Neuroscience Research Centre, Cambridge University Forvie Site, Robinson Way, Cambridge, CB2 2QB, United Kingdom. Jason.Brown@wl.com
Gee
N S
NS
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D015220:Calcium Channels / Q000235:genetics*; D002540:Cerebral Cortex / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D006801:Humans; D008969:Molecular Sequence Data; D016296:Mutagenesis; D017384:Sequence Deletion; D013552:Swine
D015220:Calcium Channels; D018076:DNA, Complementary