S. Krishna et al., Expression and functional characterization of a Plasmodium falciparum Ca2+-ATPase (PfATP4) belonging to a subclass unique to apicomplexan organisms, J BIOL CHEM, 276(14), 2001, pp. 10782-10787
We have obtained a full-length P type ATPase sequence (PfATP4) encoded by P
lasmodium falciparum and expressed PfATP4 in Xenopus laevis oocytes to stud
y its function. Comparison of the hitherto incomplete open reading frame wi
th other Ca2+-ATPase sequences reveals that PfATP4 differs significantly fr
om previously defined categories. The Ca2+-dependent ATPase activity of PfA
TP4 is stimulated by a much broader: range of [Ca2+](free) (3.2-320 muM) th
an are an avian SERCA1 pump or rabbit SERCA 1a (maximal activity < 10 <mu>M
). The activity of PfATP4 is resistant to inhibition by ouabain (200 muM) o
r thapsigargin (0.8 muM) but is inhibited by vanadate (1 mM) or cyclopiazon
ic acid (1 muM). We used a quantitative polymerase chain reaction to assay
expression of mRNA encoding PfATP4 relative to that for beta -tubulin in sy
nchronized asexual stages and found variable expression throughout the life
cycle with a maximal 5-fold increase in meronts compared with ring stages.
This analysis suggests that PfATP4 defines a novel subclass of Ca2+-ATPase
s unique to apicomplexan organisms and therefore offers potential as a drug
target.