NUP302

TgNup302 is a nuclear pore complex (NPC) component of Toxoplasma gondii, identified as the parasite orthologue of mammalian Nup98-96 and localized to the nuclear envelope by structured illumination microscopy (PMID:28138739). It is required for parasite proliferation and functions in nucleocytoplasmic transport: its conditional knock-down traps the nuclear protein TgENO2 in the cytoplasm and selectively blocks nuclear export of 18S rRNA while leaving bulk mRNA export intact, indicating a cargo-selective role at the pore (PMID:28138739). Affinity purification and reciprocal immunoprecipitation place TgNup302 in a physical network that includes additional NPC components and subunits of the FACT chromatin complex, linking the NPC to chromatin biology in this apicomplexan (PMID:28138739). Beyond these observations, no further mechanistic detail on TgNup302 has been characterized in the available corpus.

1. 2017 Medium

   Establishing whether Toxoplasma possesses a recognizable Nup98-type nucleoporin, this work identified TgNup302 as the Nup98-96 orthologue and placed it at the nuclear pore complex.

   Evidence Sequence orthology analysis plus structured illumination fluorescence microscopy in T. gondii

   PMID:28138739

   Open questions at the time

   • No structural or domain-level dissection of the FG/GLEBS regions
   • NPC substructure position (cytoplasmic vs nuclear vs central) not resolved
2. 2017 Medium

   To test whether TgNup302 is functionally important, conditional knock-down showed a proliferation delay, establishing an essential role in parasite growth.

   Evidence Tetracycline-regulated inducible knock-down (iKD) with growth assay in T. gondii

   PMID:28138739

   Open questions at the time

   • Whether the growth defect is a direct transport consequence or secondary to NPC disassembly is not distinguished
   • Residual protein levels under knock-down not quantified
3. 2017 Medium

   Addressing what transport processes TgNup302 supports, knock-down mislocalized the nuclear protein TgENO2 to the cytoplasm and selectively blocked 18S rRNA export while sparing bulk mRNA, establishing a cargo-selective role in nucleocytoplasmic transport.

   Evidence Conditional knock-down (ATc) with immunofluorescence localization of TgENO2 and FISH for 18S rRNA vs mRNA in T. gondii

   PMID:28138739

   Open questions at the time

   • Molecular basis of cargo selectivity (rRNA vs mRNA) not defined
   • Whether TgENO2 mislocalization reflects import or retention block not resolved
   • Only one import cargo tested
4. 2017 Medium

   To place TgNup302 in a molecular context, interactome analysis identified additional NPC components and FACT complex subunits, establishing a candidate NPC-chromatin link in Apicomplexa.

   Evidence Affinity tag purification with mass spectrometry and reverse immunoprecipitation, corroborated by structured illumination microscopy, in T. gondii

   PMID:28138739

   Open questions at the time

   • Functional consequence of the FACT interaction not tested
   • Whether interactions are direct or bridged by other Nups unknown
   • Stoichiometry and dynamics of the network not defined

• How TgNup302 achieves selective export of 18S rRNA over mRNA, and whether its physical association with the FACT complex functionally couples the NPC to chromatin, remain unresolved.
• No mechanism for rRNA-selective export
• Functional test of NPC-FACT coupling absent
• Structural organization of TgNup302 within the pore unknown