Molecular cloning and characterization of the human voltage-gated calcium channel α2δ-4 subunit

Abstract

The voltage-gated calcium channel is composed of a pore-forming α1 subunit and several regulatory subunits: α2δ, β, and γ. We report here the identification of a novel α2δ subunit, α2δ-4, from the expressed sequence tag database followed by its cloning and characterization. The novel α2δ-4 subunit gene contains 39 exons spanning about 130 kilobases and is colocalized with the CHCNA1C gene (α1C subunit) on human chromosome 12p13.3. Alternative splicing of the α2δ-4 gene gives rise to four potential variants, a through d. The open reading frame of human α2δ-4a is composed of 3363 base pairs encoding a protein with 1120 residues and a calculated molecular mass of 126 kDa. The α2δ-4a subunit shares 30, 32, and 61% identity with the human calcium channel α2δ-1, α2δ-2, and α2δ-3 subunits, respectively. Primary sequence comparison suggests that α2δ-4 lacks the gabapentin binding motifs characterized for α2δ-1 and α2δ-2; this was confirmed by a [3H]gabapentin-binding assay. In human embryonic kidney 293 cells, the α2δ-4 subunit associated with Cav1.2 and β3 subunits and significantly increased Cav1.2/β3-mediated Ca2+ influx. Immunohistochemical study revealed that the α2δ-4 subunit has limited distribution in special cell types of the pituitary, adrenal gland, colon, and fetal liver. Whether the α2δ-4 subunit plays a distinct physiological role in select endocrine tissues remains to be demonstrated.