Cloning and characterization of a muscle isoform of a Na,K-ATPase alpha subunit (SNaK1) from Schistosoma mansoni

A cDNA encoding a Na,K-ATPase alpha subunit homologue, designated SNaK1, wa s isolated from an adult cDNA library of Schistosoma mansoni. The 3-8 kb DN A contained a 3021 bp open reading frame potentially encoding a 1007 amino acid protein that had an M-r of 111817 and a pl of 5.48. Homology searches for SNaK1 revealed approximately 70% sequence identity with a variety of Na ,K-ATPases from evolutionarily diverse organisms. SNaK1 is predicted to con tain 10 transmembrane regions typical of this protein family as well as oth er conserved domains, such as the phosphorylation site and ATP binding doma in. Antibodies raised against an amino terminal peptide detected the protei n in membrane preparations of eggs, cercariae and adult males and females, suggesting a general role for SNaK1. The mobility of the protein differed i n various life-stages suggestive of post-transcriptional or post-translatio nal modification. Immunolocalization of SNaK1 in sections of adult worms us ing epifluorescence and electron microscopy, revealed antibody labelling in the subtegumental and peripheral layers. Strong staining NN as discernible in the peripheral muscle band indicating that SNaK1 plays a central role i n muscle contraction in adult parasites and may be the primary target of ou abain action. Staining was also detected in the secretory bodies in section s of ducts in this region and over the RER of the presumed gastrodermis. Im munogold labelling was also localized over neuronal vesicles in axons assoc iated with the peripheral muscle layer.