SEC13

PF3D7_1230700 (SEC13) is an essential nucleoporin of Plasmodium falciparum that localizes dynamically to nuclear pore complexes (NPCs) during intra-erythrocytic development, with NPC movement coupled to microtubules rather than F-actin (PMID:23687383). It is an unusual nucleoporin in that, beyond its NPC pool, SEC13 also occupies the nucleoplasm in physical association with chromatin, and its NPCs are excluded from HP1/H3K9me3-marked heterochromatin, confining pores to euchromatic territory (PMID:23687383). NPC localization persists throughout the life cycle in the P. berghei ortholog (PMID:30050042), and in P. berghei an apicomplexan-restricted C-terminal poly-proline extension of SEC13 is required for parasite survival (PMID:30050042). SEC13 is essential for P. falciparum proliferation in human erythrocytes (PMID:23687383), and a resistance-conferring mutation in SEC13 reduces P. falciparum susceptibility to the antimalarial MED6-189, linking the protein to the secretory/vesicular trafficking pathway in addition to its nuclear pore role (PMID:39325875). Beyond these observations, the detailed molecular mechanism connecting SEC13's nuclear pore, chromatin, and secretory functions has not been characterized in the available corpus.

1. 2013 Medium

   Establishing where SEC13 acts and whether its dynamics depend on cytoskeleton addressed whether this protein is a bona fide nucleoporin with regulated pore behavior; imaging placed it at NPCs moving along microtubules.

   Evidence 3D-SIM super-resolution microscopy and in vivo imaging with NPC and cytoskeletal markers in P. falciparum

   PMID:23687383

   Open questions at the time

   • Molecular basis of the microtubule coupling is unresolved
   • Does not identify SEC13's direct NPC binding partners
2. 2013 Medium

   Whether NPCs and SEC13 relate to chromatin state was unknown; co-localization and ChIP/EM showed pores avoid heterochromatin and that SEC13 additionally binds chromatin in the nucleoplasm, defining an unusual dual role.

   Evidence Co-localization with HP1/H3K9me3 markers plus ChIP and ultrastructural EM in P. falciparum

   PMID:23687383

   Open questions at the time

   • Functional consequence of SEC13 chromatin association is not defined
   • No genomic loci or gene-regulatory targets identified
3. 2013 Medium

   Whether SEC13 is required for the parasite was tested by knockdown, establishing it as essential for blood-stage proliferation.

   Evidence PNA-mediated knockdown of PfSec13 with parasite proliferation readout in P. falciparum

   PMID:23687383

   Open questions at the time

   • Single knockdown method, no genetic complementation
   • Does not distinguish which SEC13 function (NPC vs chromatin) underlies essentiality
4. 2013 Low

   Sequence/structure analysis addressed why SEC13 behaves unusually, predicting it is a Sec13–Nup145C fusion protein.

   Evidence Bioinformatic structural similarity analysis

   PMID:23687383

   Open questions at the time

   • Computational prediction only, no structural or mutagenesis validation
   • Fusion architecture not experimentally confirmed
5. 2018 Medium

   Whether SEC13's unusual domain features matter for viability was tested in P. berghei, showing an apicomplexan-specific C-terminal poly-proline extension is essential and confirming NPC localization across the life cycle.

   Evidence Genetic functional analysis, GFP-tagged Nup imaging, and cryo-electron tomography in P. berghei

   PMID:30050042

   Open questions at the time

   • Molecular function of the poly-proline extension is unknown
   • Findings in P. berghei not directly reproduced for the P. falciparum ortholog
6. 2024 Medium

   A drug-resistance screen unexpectedly implicated SEC13 in secretory/vesicular trafficking, extending its role beyond the nuclear pore.

   Evidence Genomic identification of a MED6-189 resistance-conferring SEC13 mutation in P. falciparum

   PMID:39325875

   Open questions at the time

   • Pathway placement is inferred from drug mode-of-action, not direct trafficking assay
   • How a single mutation confers resistance is not mechanistically defined
   • Relationship between SEC13's nuclear-pore and secretory roles is unresolved

• It remains unknown how SEC13's distinct activities — nuclear pore function, chromatin association, and secretory/vesicular trafficking — are mechanistically integrated within a single protein.
• No direct interaction map of SEC13 in either compartment
• No structural validation of the predicted fusion architecture
• No assay directly connecting the drug-resistance mutation to a trafficking defect