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

The primary structure of a calcium channel beta subunit (beta 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 beta M mRNA is predominantly expressed in neuronal tissues. Transcription of beta 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 beta M and mammalian beta subunits is lower (66-68%) than within mammalian beta subunits (74-80%). Calculation of a phylogenetic tree indicates that beta M is an ancestral form of the four distinct beta subunit gene products identified in mammalian tissues so far. Despite these sequence differences, beta 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 alpha 1 cDNA in the same manner as was previously shown for mammalian beta subunits.