PKNH_1300700

PKNH_1300700 encodes a Plasmodium tryptophan-rich domain protein; no direct experiments have been performed on the P. knowlesi protein itself, and its function is inferred entirely from characterized orthologs and family members in other Plasmodium species. In P. berghei, the orthologous protein IPIS2 localizes to intraerythrocytic Plasmodium-induced membrane structures (IBIS) and to the liver-stage parasitophorous vacuole membrane, associates with the IBIS component IBIS1, and is required for efficient CD36-mediated binding and sequestration of infected erythrocytes out of circulation (PMID:36126089). Another family member, SLTRiP, forms large multimers and is exported into the cytosol of infected hepatocytes, where it supports normal liver-stage development (PMID:25960542). Beyond these ortholog and family-member studies, no mechanistic detail specific to PKNH_1300700 has been characterized in the available corpus.

1. 2011 Low

   The first question was whether members of this Plasmodium-specific tryptophan-rich family have any functional consequence for the parasite; a P. falciparum family member (PArt) was linked to drug tolerance and possible essentiality, establishing that these proteins are not inert.

   Evidence Immunodetection dose-response, transgenic overexpression with artesunate survival assay and failed gene disruption in P. falciparum, plus HMM family classification

   PMID:21464256

   Open questions at the time

   • Overexpression phenotype from a single lab with no direct molecular mechanism established; gene-disruption failure is inconclusive for essentiality
   • Concerns a P. falciparum family member (PArt), not PKNH_1300700 or its direct ortholog
   • No localization or interaction data for PKNH_1300700 itself
2. 2015 Medium

   To ask what these tryptophan-rich proteins do at the cell-biological level, the family member SLTRiP was shown to multimerize and to be exported into the hepatocyte cytosol, defining an auxiliary role in liver-stage development.

   Evidence Biochemical multimerization assay, IFA localization/export, gene knockout with 18S rRNA liver-stage readout and transcriptome profiling in P. berghei

   PMID:25960542

   Open questions at the time

   • The molecular partners and export machinery for SLTRiP are not defined
   • Findings are for a P. berghei family member, not experimentally shown for PKNH_1300700
   • Only a moderate, non-essential developmental phenotype was observed
3. 2022 Medium

   The mechanistic peak so far assigned a concrete host-interaction role: the PKNH_1300700 ortholog IPIS2 associates with IBIS1, localizes to induced membrane structures and the liver-stage PVM, and is required for CD36-mediated sequestration of infected erythrocytes.

   Evidence Reciprocal Co-IP/MS with IBIS1, immunofluorescence localization, gene deletion, and CD36-binding adhesion assay in P. berghei

   PMID:36126089

   Open questions at the time

   • Single lab, single study; direct binding of the protein to CD36 versus an indirect requirement is not resolved
   • How the protein reaches the erythrocyte surface and organizes IBIS is unknown
   • Demonstrated in P. berghei ortholog, not in PKNH_1300700 itself

• Whether PKNH_1300700 of P. knowlesi shares the localization, IBIS/PVM association, multimerization, export, and CD36-sequestration functions of its P. berghei orthologs remains entirely untested.
• No localization, interaction, knockout, or adhesion data exist for PKNH_1300700 itself
• It is unknown whether P. knowlesi sequestration depends on this protein
• The relationship between the erythrocytic (IBIS/CD36) and liver-stage roles is unresolved even in orthologs