A cation-transporting ATPase gene of Plasmodium yoelii was cloned from the parasite genomic library using an oligonucleotide probe derived from a conserved amino acid sequence of the phosphorylation domain of the aspartyl phosphate family of ATPases. The complete nucleotide sequence was determined and it predicts a 126,717 Mr encoded protein composed of 1115 amino acids. Northern blot analysis revealed that the gene is transcribed during the asexual stages of parasite development. The P. yoelii protein contains functional and structural features common to the family of aspartyl phosphate cation-transporting ATPases. The parasite protein shows the highest overall homology in amino acid sequence (42%) to the Ca2(+)-ATPase of rabbit skeletal muscle sarcoplasmic reticulum. Homologies to other aspartyl phosphate cation-transporting ATPases including a plasma membrane Ca2(+)-ATPase were between 13 and 24%. The structure predicted from a hydropathy plot also shows 10 transmembrane domains, the number and location of which correlated well with the sarcoplasmic reticulum Ca2(+)-ATPase. On the basis of these results, we conclude that the parasite gene encodes an organellar, but not plasma membrane, Ca2(+)-ATPase. The P. yoelii protein, furthermore, contains all six amino acid residues in the transmembrane domains that were recently identified as comprising a high-affinity Ca2(+)-binding site. It follows that organellar Ca2(+)-ATPases of rabbit and Plasmodium conserve functionally important amino acid residues, even though they are remote from each other phylogenetically.
Amino-acid sequence of parvalbumin from rabbit skeletal muscle.
