GRP170

GRP170 (PF3D7_1344200) is an endoplasmic reticulum-resident chaperone of Plasmodium falciparum that is essential for asexual blood-stage development, being specifically required for proper schizont maturation (PMID:31087747). It functions as a partner of the ER Hsp70 chaperone BiP (PfHsp70-2), with which it physically associates (PMID:31087747), and as an independent chaperone it exhibits basal ATPase activity and suppresses heat-induced aggregation of a model substrate in a nucleotide-independent holdase mode (PMID:40730633); ATP binding itself destabilizes the protein, rendering it more susceptible to heat stress and proteolysis (PMID:40730633). GRP170 is critical for parasite survival under heat shock and acts upstream of the eIF2α kinase PK4 in the stress-response pathway, since loss of GRP170 function triggers PK4 activation (PMID:31087747). GRP170 also co-precipitates with the invasion ligand PfRh5, although its loss does not impair PMX-mediated processing of PfRh5, indicating this association is not required for that step (PMID:37072430).

1. 2019 High

   Establishing where GRP170 acts and whether it matters answered the basic question of its cellular role: it is an ER-resident, essential chaperone with a stage-specific requirement.

   Evidence Conditional mutagenesis with inducible loss-of-function and fluorescence microscopy in P. falciparum

   PMID:31087747

   Open questions at the time

   • Molecular basis of the schizont-stage specificity not defined
   • Substrate repertoire in the ER not identified
2. 2019 Medium

   Identifying a binding partner placed GRP170 within the ER chaperone machinery by showing it physically associates with BiP/Hsp70-2.

   Evidence Co-immunoprecipitation from parasite lysate

   PMID:31087747

   Open questions at the time

   • Single Co-IP without reciprocal validation
   • Whether GRP170 acts as a nucleotide-exchange factor for BiP not tested
3. 2019 Medium

   Linking GRP170 loss to PK4 activation and heat-shock lethality connected the chaperone to the parasite stress-response pathway and placed it genetically upstream of the eIF2α kinase.

   Evidence Conditional knockdown with PK4 activation readout and heat-shock survival assay in P. falciparum

   PMID:31087747

   Open questions at the time

   • Mechanism by which GRP170 loss activates PK4 not resolved
   • Direct versus indirect epistasis with PK4 not distinguished
4. 2023 Medium

   Testing a physical association with the invasion ligand PfRh5 clarified the functional boundaries of GRP170, showing it associates with PfRh5 but is dispensable for PfRh5 processing.

   Evidence Pull-down from parasite lysate plus inducible knockout with growth and PMX-processing assays in P. falciparum

   PMID:37072430

   Open questions at the time

   • Functional consequence of the PfRh5 association unknown
   • Whether the interaction is direct or complex-mediated not established
5. 2025 High

   Biochemical reconstitution answered whether GRP170 has intrinsic chaperone activity, demonstrating basal ATPase activity and nucleotide-independent holdase function, and revealing that ATP binding destabilizes the protein.

   Evidence In vitro ATPase and aggregation-suppression assays, circular dichroism, proteolysis assays, and molecular dynamics with recombinant E. coli-expressed protein

   PMID:40730633

   Open questions at the time

   • Physiological substrates in vivo not identified
   • Relationship between ATP-induced destabilization and holdase cycle not defined

• How GRP170 cooperates with BiP mechanistically and what its endogenous ER client proteins are remain open.
• No native substrate identified
• Molecular mechanism coupling GRP170 to PK4-mediated stress signaling not established
• Structural model of GRP170-BiP cooperation absent