SEC31

SEC31 (PF3D7_0214100) is a COPII outer-coat protein of Plasmodium that functions in vesicle-mediated protein trafficking during the blood stage (PMID:11591825, PMID:30050042). In P. falciparum-infected erythrocytes it is expressed as an ~160 kDa protein absent from uninfected cells, is largely insoluble in nonionic detergent (consistent with cytoskeletal attachment), and localizes partly within the parasite and partly to erythrocyte-cytoplasmic structures that overlap with the COPII GTPase PfSar1p and the cytoadherence virulence protein PfEMP1, linking it to trafficking of parasite proteins beyond the parasite plasma membrane (PMID:11591825). In P. berghei, endogenously tagged SEC31 forms discrete cytoplasmic puncta distinct from the nucleus with a distribution matching SEC13 and SEC16, consistent with COPII coat function at transitional ER exit sites across trophozoite, gametocyte, and sporozoite stages (PMID:30050042). Domain analysis indicates that Haemosporidia SEC31, including the P. falciparum ortholog, retains the Sec16_C domain found in human SEC31, unlike SEC31 from other apicomplexan clades (PMID:30704415). Beyond these localization and domain-level observations, the biochemical activity and interaction partners of SEC31 have not been characterized in the available corpus.

1. 2001 Medium

   Establishing whether a COPII coat component participates in trafficking beyond the parasite boundary addressed how Plasmodium exports virulence factors into the host cell; SEC31 was shown to reside partly in the erythrocyte cytoplasm alongside PfSar1p and PfEMP1.

   Evidence Western blot with anti-recombinant-domain antibodies, Triton X-100 solubility fractionation, and confocal co-localization in P. falciparum-infected erythrocytes

   PMID:11591825

   Open questions at the time

   • Co-localization does not demonstrate direct physical interaction with PfSar1p or PfEMP1
   • No functional perturbation (knockdown/knockout) to test a causal role in PfEMP1 export or cytoadherence
   • Basis of detergent insolubility / proposed cytoskeletal attachment not molecularly defined
2. 2018 Medium

   Whether SEC31 behaves as a canonical COPII coat protein at ER exit sites in vivo was tested by endogenous tagging, showing punctate distribution matching SEC13 and SEC16 across multiple life-cycle stages.

   Evidence Endogenous C-terminal mCherry tagging with live-cell imaging, comparison to SEC13-GFP and SEC16-mCherry, and ER Tracker co-staining in P. berghei

   PMID:30050042

   Open questions at the time

   • Does not establish assembly into a functional COPII coat complex biochemically
   • No test of an exported/erythrocyte-cytoplasmic pool as reported in P. falciparum
   • Functional consequence of the puncta redistribution during sporozoite maturation unresolved
3. 2019 Low

   Whether SEC31 domain architecture in malaria parasites differs from other apicomplexans was assessed computationally, revealing retention of the human-like Sec16_C domain in Haemosporidia.

   Evidence In silico domain composition and phylogenetic analysis of SEC31 across apicomplexan genomes

   PMID:30704415

   Open questions at the time

   • Computational prediction only, with no experimental validation of the Sec16_C domain function
   • Functional significance of domain retention for SEC16 interaction or coat assembly untested

• Whether SEC31 is functionally required for COPII-mediated trafficking or for PfEMP1 export and cytoadherence, and whether it directly interacts with PfSar1p, SEC13, or SEC16, remains unresolved.
• No genetic knockout/knockdown phenotype for SEC31
• No reciprocal biochemical demonstration of COPII complex membership
• No direct evidence linking SEC31 to virulence-factor export function