Calcium Channel α2δ Subunits—Structure and Gabapentin Binding

Abstract

High-voltage activated calcium channels are modulated by a series of auxiliary proteins, including those of the α2δ family. Until recently, only a single α2δ subunit was known, but two further members, α2δ-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 α2δ-1, both α2δ-2 and -3 subunits consist of two proteins—a larger α2 and a smaller δ that can be separated by reduction. The subunits are also highly N-glycosylated with approximately 30 kDa of their mass consisting of oligosaccharides. α2δ-1 was detected in all mouse tissues studied, whereas α2δ-2 was found at high levels in brain and heart. The α2δ-3 subunit was observed only in brain. α2δ-1 and α2δ-2, but not α2δ-3, were found to bind gabapentin. TheKd value of gabapentin binding to α2δ-2 was 153 nM compared with the higher affinity binding to α2δ-1 (Kd = 59 nM).