PARE

PARE (PF3D7_0709700) is a membrane-associated serine hydrolase expressed throughout the P. falciparum intraerythrocytic cycle whose native de-esterification activity is co-opted both for lipid metabolism and for antimalarial prodrug activation (PMID:28106035, PMID:41043577). It behaves as a bona fide active-site serine hydrolase in the asexual blood stage, where it is captured by fluorophosphonate activity-based probes in situ (PMID:31772212), and it hydrolyzes ester bonds in a range of substrates in vitro, activating the esterified prodrugs pepstatin esters and MMV011438 through de-esterification (PMID:28106035). Because compound potency depends on this activation step, loss-of-function mutations in PARE confer resistance to pepstatin esters and MMV011438 (PMID:28106035) and to the lindenane sesquiterpenoid dimer chlorajaponilide C (PMID:32970404). Biologically, PARE localizes to the parasite periphery and contributes to hydrolysis of lysophosphatidylcholine (LPC); it is a minor, redundant player in this process, since its disruption alone causes negligible fitness defect and does not impair fatty acid scavenging, whereas combined loss of PARE with XL2 and XLH4 blocks scavenging of choline and fatty acids from LPC and prevents replication when LPC is the sole exogenous fatty acid source (PMID:36189342, PMID:41043577). Beyond these roles in LPC hydrolysis and prodrug activation, no further mechanistic detail for PARE has been characterized in the available corpus.

1. 2017 High

   Establishing that a parasite esterase can activate esterified antimalarials answered how certain prodrugs become active and revealed a genetic route to resistance.

   Evidence In vitro resistance selection with whole-genome sequencing plus recombinant enzyme assays on pepstatin esters and MMV011438 in P. falciparum

   PMID:28106035

   Open questions at the time

   • Native physiological substrate not defined at this stage
   • Structural basis of ester recognition not resolved
   • Subcellular location not established
2. 2019 Medium

   Demonstrating that PARE is labeled by a serine-hydrolase active-site probe in intact parasites confirmed that the enzyme is catalytically active in its native context, not just as a recombinant protein.

   Evidence Fluorophosphonate-based activity-based protein profiling with mass spectrometry in asexual erythrocytic-stage P. falciparum

   PMID:31772212

   Open questions at the time

   • Single method and single lab for this protein
   • Does not identify endogenous substrate
   • Activity not quantified against specific lipids
3. 2020 Medium

   Extending resistance genetics to a structurally distinct compound class showed the prodrug-activation role generalizes, while SAR indicated the dependence is compound-specific.

   Evidence In vitro resistance selection, whole-genome sequencing, and structure-resistance analysis across chlorajaponilide-related sesquiterpenoid dimers in P. falciparum

   PMID:32970404

   Open questions at the time

   • Direct enzymatic de-esterification of chlorajaponilide C not shown in vitro
   • Basis for which dimers require PARE not molecularly defined
   • Single lab
4. 2022 Medium

   Genetic disruption clarified that PARE is dispensable for parasite viability, framing its endogenous role as non-essential and redundant.

   Evidence CRISPR-based mNeonGreen reporter insertion/disruption with competitive fitness assay and expression profiling in P. falciparum Dd2

   PMID:36189342

   Open questions at the time

   • Endogenous function not identified by disruption alone
   • Redundant partners not tested here
   • Single method
5. 2025 Medium

   Combining localization and epistasis assigned PARE a concrete but redundant physiological role in lysophosphatidylcholine hydrolysis at the parasite periphery.

   Evidence Single and combinatorial knockdown of PARE with XL2/XLH4, growth assays in defined media with LPC as sole fatty acid source, and subcellular localization in P. falciparum

   PMID:41043577

   Open questions at the time

   • Individual catalytic contribution of PARE to LPC hydrolysis not quantified
   • Relationship between LPC hydrolysis and prodrug activation not resolved
   • Membrane topology not defined

• It remains unknown how a single peripheral esterase reconciles its minor endogenous LPC-hydrolysis role with its capacity to activate structurally diverse prodrugs, and what structural features govern substrate selection.
• No structural model of the active site
• Full endogenous substrate spectrum undefined
• Mechanistic link between metabolic and prodrug-activating activities unresolved