APC3

APC3 (PF3D7_0501700) is a subunit of the anaphase-promoting complex/cyclosome (APC/C) E3 ubiquitin ligase that governs the atypical, closed mitotic divisions of Plasmodium (PMID:29618731). In P. berghei, APC3 localizes as a single focus coinciding with the centriolar plaque during asexual schizogony and resolves into multiple foci in male gametocytes, linking its distribution to the sites of spindle organization during proliferative stages (PMID:29618731). Loss-of-function studies in P. berghei establish that APC3 is essential during mitosis: its disruption abolishes chromosome condensation, produces abnormal cytokinesis, and prevents microgamete formation during male gametogenesis (PMID:29618731). All available mechanistic evidence derives from the P. berghei ortholog; the function of PF3D7_0501700 during P. falciparum blood-stage schizogony has not been characterized in the available corpus, and no direct biochemical demonstration of its E3 ligase activity, substrate targets, or interaction map is present.

1. 2018 Medium

   To place APC3 in the cell-division machinery, its subcellular distribution across proliferative stages was resolved, revealing an association with the centriolar plaque that ties it to the spindle-organizing center during closed mitosis.

   Evidence Live-cell imaging combined with reverse genetics (gene disruption and conditional knockdown) in P. berghei

   PMID:29618731

   Open questions at the time

   • The molecular basis of centriolar-plaque recruitment is not defined
   • Localization was characterized in P. berghei only, not for P. falciparum PF3D7_0501700
   • No demonstration that the imaged foci represent an assembled, active APC/C complex
2. 2018 High

   To test whether APC3 is functionally required rather than merely present, orthogonal loss-of-function approaches defined discrete mitotic phenotypes, establishing APC3 as an essential APC/C component for chromosome condensation, cytokinesis, and microgametogenesis.

   Evidence Gene disruption plus conditional knockdown with phenotypic readouts (chromosome condensation, cytokinesis, microgamete formation) in P. berghei

   PMID:29618731

   Open questions at the time

   • The ubiquitination substrates of the APC3-containing APC/C in Plasmodium are not identified
   • Direct E3 ligase activity and the composition of the APC/C complex are not biochemically reconstituted
   • Requirement during P. falciparum blood-stage schizogony is untested

• Whether PF3D7_0501700 performs the same essential APC/C role during P. falciparum asexual and sexual development, and which cell-cycle substrates it targets for ubiquitination, remains unresolved.
• No functional characterization of PF3D7_0501700 in P. falciparum
• No substrate or interaction data for the Plasmodium APC/C
• No structural model of the APC3 subunit or complex