Structural requirement of the calcium-channel subunit α2δ for gabapentin binding

Gabapentin [Neurontin, 1-(aminomethyl)cyclohexaneacetic acid] is a novel anticonvulsant drug with a high binding affinity for the Ca#+-channel subunit α # δ. In this study, the gabapentin-binding properties of wild-type and mutated porcine brain α # δ proteins were investigated. Removal of the disulphide bonds between the α # and the δ subunits did not result in a significant loss of gabapentin binding, suggesting that the disulphide linkage between the two subunits is not required for binding. Singly expressed α # protein remained membrane associated. However, α # alone was unable to bind gabapentin, unless the cells were concurrently transfected with the expression vector for δ, suggesting that both α # and δ are required for gabapentin binding. Using internal deletion mutagenesis, we mapped two regions [amino acid residues 339–365 (∆F) and 875–905 (∆J)] within the α # subunit that are not required for gabapentin binding. Further, deletion of three other individual regions