Calcium channel alpha(2)delta subunits-structure and Gabapentin binding.

High-voltage activated calcium channels are modulated by a series of auxiliary proteins, including those of the alpha(2)delta family. Until recently, only a single alpha(2)delta subunit was known, but two further members, alpha(2)delta-2 and -3, have since been identified. In this study, the structure of these two novel subunits has been characterized and binding of the antiepileptic drug gabapentin investigated. Using antibodies directed against the amino terminal portion of the proteins, the gross structure of the subunits could be analyzed by Western blotting. Similar to alpha(2)delta-1, both alpha(2)delta-2 and -3 subunits consist of two proteins-a larger alpha(2) and a smaller delta that can be separated by reduction. The subunits are also highly N-glycosylated with approximately 30 kDa of their mass consisting of oligosaccharides. alpha(2)delta-1 was detected in all mouse tissues studied, whereas alpha(2)delta-2 was found at high levels in brain and heart. The alpha(2)delta-3 subunit was observed only in brain. alpha(2)delta-1 and alpha(2)delta-2, but not alpha(2)delta-3, were found to bind gabapentin. The K(d) value of gabapentin binding to alpha(2)delta-2 was 153 nM compared with the higher affinity binding to alpha(2)delta-1 (K(d) = 59 nM).