HAD2

HAD2 (PF3D7_1226300) is a phosphatase of the haloacid dehalogenase-like hydrolase superfamily in Plasmodium falciparum that acts as a regulator of central carbon and isoprenoid-precursor metabolism (PMID:30425143). Its phosphatase activity normally constrains the steady-state levels of methylerythritol phosphate (MEP) pathway and glycolytic intermediates; loss-of-function mutations elevate these metabolites and confer resistance to fosmidomycin, a drug targeting the MEP pathway (PMID:30425143). Genetically, HAD2 sits upstream of or in parallel with the glycolytic enzyme PFK9: hypomorphic PFK9 mutations suppress the growth defect and restore fosmidomycin sensitivity of HAD2-deficient parasites, placing HAD2 within a metabolic-homeostasis circuit that also governs drug sensitivity (PMID:30425143). Beyond this phosphatase-and-metabolic-regulation role established in P. falciparum 3D7, no further mechanistic detail — including its direct physiological substrate — has been characterized in the available corpus.

1. 2018 High

   Whether any parasite factor could modulate sensitivity to fosmidomycin through metabolism was unknown; identifying HAD2 as a HAD-superfamily phosphatase whose loss confers resistance established a new metabolic node controlling drug sensitivity.

   Evidence In vitro phosphatase assay plus forward genetic selection of fosmidomycin-resistant mutants and metabolic profiling in P. falciparum 3D7

   PMID:30425143

   Open questions at the time

   • The direct physiological substrate of HAD2 is not identified
   • The structural basis of its phosphatase activity is not resolved
   • How loss-of-function alleles reduce or abolish activity mechanistically is not defined
2. 2018 High

   It was unclear how HAD2 loss produced resistance; showing that loss elevates MEP-pathway and glycolytic intermediates and that PFK9 hypomorphs suppress the phenotype placed HAD2 in a metabolic-regulatory circuit upstream of or parallel to glycolysis.

   Evidence Metabolic profiling of resistant and suppressed strains plus a forward genetic suppressor screen and epistasis analysis in P. falciparum 3D7

   PMID:30425143

   Open questions at the time

   • Whether HAD2 acts directly on glycolytic/MEP intermediates or through an intermediary is not established
   • The molecular basis of the genetic interaction between HAD2 and PFK9 is not resolved
   • Physiological function of HAD2 outside the drug-resistance context is not characterized

• The direct enzymatic substrate of HAD2 and the precise mechanism by which it constrains metabolic flux remain unknown.
• No physiological substrate identified in the available corpus
• No structural model of HAD2
• Subcellular localization of HAD2 is not characterized