Cloning and functional expression of a neuronal calcium channel β subunit from house fly (Musca domestica)

Abstract

The primary structure of a calcium channel β subunit (β(M)) from housefly (Musca domestica) has been deduced by cDNA cloning and sequence analysis. The open reading frame encodes a 441-amino acid polypeptide with a calculated molecular mass of 48,755 Da. Whole-mount in situ hybridization indicates that β(M) mRNA is predominantly expressed in neuronal tissues. Transcription of β(M) mRNA is evident from stage 13/14 of embryogenesis up to adulthood. Different expression patterns of splice variants were found in larvae and in adult fly heads. Amino acid identity between β(M) and mammalian β subunits is lower (66-68%) than within mammalian β subunits (74-80%). Calculation of a phylogenetic tree indicates that β(M) is an ancestral form of the four distinct β subunit gene products identified in mammalian tissues so far. Despite these sequence differences, β(M) is able to enhance endogenous calcium channel activity in Xenopus laevis oocytes as well as dihydropyridine binding to membranes from COS 7 cells transfected with rabbit heart α1 cDNA in the same manner as was previously shown for mammalian β subunits.