Complementary DNA was isolated, encoding a putative Ca(2+)-transport ATPase (SMA1) of the human parasitic trematode Schistosoma mansoni. The cDNA was isolated by a nested polymerase chain reaction based strategy. The oligonucleotides used were designed on the basis of conserved amino-acid regions found in P-type ATPases. The complete nucleotide sequence was determined. The primary structure and topology of the enzyme were deduced. SMA1 has 1022 amino acids and a predicted molecular mass of 113 kDa. This protein is 67% identical and phylogenetically related to several sarco/endoplasmic reticulum Ca(2+)-ATPases but lacks the phospholamban-binding domain that exists in the SERCA isoforms 1 and 2. The membrane topology predicted for SMA1 is characteristic of the P-type ATPases, showing two major cytoplasmic loops and ten conserved hydrophobic segments. Sequences and residues that are important for the function of the SER Ca(2+)-ATPase, such as the high-affinity Ca(2+)-binding sites, the putative fluorescein isothiocyanate binding site, the 5'-(p-fluorosulfonyl)benzoyladenosine binding site and the aspartyl phosphorylation site, are conserved in SMA1, suggesting that the cloned gene is a Ca(2+)-transport ATPase of the SERCA family. In addition, three PCR products were cloned which share homology with another SER Ca(2+)-ATPase, with the yeast secretory pathway Ca(2+)-ATPase PMR1 and its mammalian homologue, and with the alpha subunit of a Na+,K(+)-ATPase.