Cloning and characterization of a calcium channel α1 subunit from Drosophila melanogaster with similarity to the rat brain type D isoform

Abstract

We report the complete sequence of a calcium Channel α1 subunit cDNA cloned from a Drosophila head cDNA library. This cDNA encodes a deduced protein containing 2516 amino acids with a predicted molecular weight of 276,493. The deduced protein shares many features with vertebrate homologs, including four repeat structures, each containing six transmembrane domains, a conserved ion selectivity filter region between transmembrane domains 5 and 6, and an EF hand in the carboxy tail. The Drosophila subunit has unusually long initial amino and terminal carboxy tails. The region corresponding to the last transmembrane domain (IVS6) and the adjacent cytoplasmic domain has been postulated to form a phenylalkylamine-binding site in vertebrate calcium channels. This region is conserved in the Drosophila sequence, while domains thought to be involved in dihydropyridine binding show numerous changes. The Drosophila subunit exhibits 78.3% sequence similarity to the rat brain type D calcium channel α1 subunit, and so has been designated as a Drosophila melanogaster calcium channel α1 type D subunit (Dmca 1D). In situ hybridization shows that Dmca 1D is highly expressed in the embryonic nervous system. Northern analysis shows that Dmca 1D cDNA hybridizes to three size classes of mRNA (9.5, 10.2, and 12.5 kb) in heads, but only two classes (9.5 and 12.5 kb) in bodies and legs. PCR analysis suggests that the Dmca 1D message undergoes alternative splicing with more heterogeneity appearing in head and embryonic extracts than in bodies and legs.