PF3D7_1319700

PF3D7_1319700 encodes a PP2A-like Ser/Thr protein phosphatase active in the cytosol of P. falciparum erythrocytic stages, where it dephosphorylates phosphoserine/phosphothreonine substrates including the alpha subunit of phosphorylase kinase; the enzyme requires Mn2+, is resistant to inhibitor-1, and is inhibited by nanomolar okadaic acid, the biochemical signature by which its catalytic activity was first defined (PMID:10340482). Its activity is tuned by two dedicated parasite regulators: the SET/TAF-family aspartate-rich protein PfARP specifically inhibits PF3D7_1319700 at nanomolar concentrations without affecting PP1, PP2B, PP5, or PPJ (PMID:12615323), while PfPTPA physically binds and activates the phosphatase, an interaction dependent on PfPTPA residues V283, G292, and M296 and with G292 essential for activation (PMID:24521882). PfPTPA and PF3D7_1319700 co-localize in the same compartment of blood-stage parasites (PMID:24521882). Note that the timeline characterizes PF3D7_1319700 primarily through the enzymology of its purified activity and the identity of its regulators; the discrete substrate repertoire, physiological targets, and in vivo role of this phosphatase have not been characterized in the available corpus.

1. 1999 Medium

   Whether P. falciparum possesses a distinct PP2A-type phosphatase was unknown; biochemical purification defined a Mn2+-dependent, okadaic acid-sensitive cytosolic enzyme and linked it to the PF3D7_1319700 catalytic subunit, establishing the enzyme's existence and core catalytic properties.

   Evidence biochemical purification of phosphatase activity from erythrocytic-stage cytosolic extracts, substrate specificity and inhibitor profiling, cDNA cloning matched to N-terminal sequence of the purified enzyme

   PMID:10340482

   Open questions at the time

   • physiological substrates beyond phosphorylase kinase alpha subunit not identified
   • subcellular and stage-specific localization not resolved
   • no genetic or in vivo functional test of the enzyme
2. 2003 Medium

   How the phosphatase is negatively regulated was unaddressed; the SET/TAF-family protein PfARP was shown to inhibit PF3D7_1319700 at nanomolar concentrations without acting on other parasite phosphatases, identifying a specific candidate physiological inhibitor.

   Evidence in vitro phosphatase inhibition assays with purified native and recombinant PfARP against PP2A, PP1, PP2B, PP5, and PPJ

   PMID:12615323

   Open questions at the time

   • physical binding site of PfARP on PF3D7_1319700 not mapped
   • in vivo relevance of the inhibition not demonstrated
   • conditions triggering PfARP-mediated inhibition unknown
3. 2014 Medium

   The positive regulatory input to the phosphatase was undefined; PfPTPA was shown to bind and activate PF3D7_1319700 and to co-localize with it in blood stages, with mutagenesis pinpointing V283, G292, and M296 as the interaction determinants and G292 as essential for activation, establishing the molecular basis of an activating partner.

   Evidence in vitro binding and PP2A activity assays, site-directed mutagenesis of PfPTPA, subcellular co-localization in blood-stage parasites, Xenopus oocyte functional assays

   PMID:24521882

   Open questions at the time

   • interaction interface on PF3D7_1319700 itself not defined
   • downstream substrates activated by the PfPTPA-PfPP2A complex not identified
   • no genetic disruption to confirm the pathway in vivo

• The endogenous substrate repertoire, in vivo role in intraerythrocytic development, and structural basis of regulator binding for PF3D7_1319700 remain to be determined.
• no physiological substrate map
• no genetic knockout/knockdown phenotype
• no structural model of PF3D7_1319700 or its regulator complexes