Characterization of the ATP4 ion pump in .

The ATPase ATP4 is the target of a diverse range of antimalarial compounds, including the clinical drug candidate cipargamin. ATP4 was originally annotated as a Ca 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 , ATP4. We show that ATP4 is a plasma membrane protein. Knockdown of ATP4 had no effect on resting pH or Ca but rendered parasites unable to regulate their cytosolic Na concentration ([Na]). ATP4 inhibitors caused an increase in [Na] and a cytosolic alkalinization in WT but not ATP4 knockdown parasites. Parasites in which ATP4 was knocked down or disrupted exhibited a growth defect, attributable to reduced viability of extracellular parasites. Parasites in which ATP4 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.