Characterization of the ATP4 ion pump in Toxoplasma gondii.
Lehane AM., Dennis ASM., Bray KO., Li D., Rajendran E., McCoy JM., McArthur HM., Winterberg M., Rahimi F., Tonkin CJ., Kirk K., van Dooren GG.
The Plasmodium falciparum ATPase PfATP4 is the target of a diverse range of antimalarial compounds, including the clinical drug candidate cipargamin. PfATP4 was originally annotated as a Ca2+ transporter, but recent evidence suggests that it is a Na+ efflux pump, extruding Na+ in exchange for H+ Here we demonstrate that ATP4 proteins belong to a clade of P-type ATPases that are restricted to apicomplexans and their closest relatives. We employed a variety of genetic and physiological approaches to investigate the ATP4 protein of the apicomplexan Toxoplasma gondii, TgATP4. We show that TgATP4 is a plasma membrane protein. Knockdown of TgATP4 had no effect on resting pH or Ca2+, but rendered parasites unable to regulate their cytosolic Na+ concentration ([Na+]cyt). PfATP4 inhibitors caused an increase in [Na+]cyt and a cytosolic alkalinization in wild type, but not in TgATP4-knockdown, parasites. Parasites in which TgATP4 was knocked down or disrupted exhibited a growth defect, attributable to a reduced viability of extracellular parasites. Parasites in which TgATP4 had been disrupted showed reduced virulence in mice. These results provide evidence for ATP4 proteins playing a key, conserved role in Na+ regulation in apicomplexan parasites.