CCT2

CCT2/PF3D7_0306800 is a subunit of the oligomeric TRiC/CCT chaperonin complex of Plasmodium falciparum, and its characterized biology in the available corpus is confined to its membership in this complex rather than any function demonstrated for the subunit itself (PMID:36567946). Affinity purification of the parasite CCT complex from trophozoite-stage parasites identified CCT2 among the oligomeric subunits, with the complex engaging clients including actin, tubulin, and WD40 propeller proteins (PMID:36567946). The complex localizes within the parasite cytosol and is not exported into the host erythrocyte; regulatable knockdown of a different subunit (TRiC-θ) causes a severe asexual growth defect without disrupting protein export, establishing that the complex is essential for intra-parasite biology (PMID:28067475). The complex has additionally been co-immunoprecipitated with Maurer's cleft membrane proteins such as PfSBP1 (PMID:25615740) and, in P. yoelii, with the CAF1/CCR4/NOT mRNA-decay machinery (PMID:30703164), but these associations are attributed to the complex and no mechanistic role has been demonstrated for the CCT2 subunit specifically beyond its incorporation into PfCCT.

1. 2015 Low

   To ask whether the parasite chaperonin machinery participates in trafficking exported host-cell remodeling proteins, the PfTRiC complex was tested for interaction with Maurer's cleft membrane cargo.

   Evidence Co-immunoprecipitation, domain mapping, and localization in P. falciparum-infected erythrocytes, identifying the PfSBP1 N-terminal domain as the interaction site

   PMID:25615740

   Open questions at the time

   • Single Co-IP/pulldown from one lab without reciprocal validation
   • Interaction attributed to the complex, not to the CCT2 subunit specifically
   • No functional test that CCT2 is required for PfSBP1 trafficking
2. 2017 Medium

   To determine where the parasite TRiC complex acts and whether it is essential, its localization and the consequence of subunit depletion were assessed.

   Evidence Parasite-specific antibody, epitope-tagged transgenic parasites, and regulatable knockdown of the TRiC-θ subunit with growth and protein-export assays in P. falciparum

   PMID:28067475

   Open questions at the time

   • Knockdown targeted TRiC-θ, not CCT2, so CCT2's individual essentiality is inferred from complex membership
   • Cytosolic confinement established for the complex, not shown for CCT2 in isolation
   • No molecular activity assigned to any single subunit
3. 2019 Low

   To map protein networks around the CCR4/NOT deadenylation machinery, its interactors were profiled, incidentally detecting TRiC subunits including CCT2.

   Evidence GFP immunoprecipitation followed by mass spectrometry with SAINT scoring of PyCCR4-1::GFP from synchronized P. yoelii schizonts

   PMID:30703164

   Open questions at the time

   • CCT2 detected only at low-confidence SAINT scores (0.1–0.35)
   • No functional follow-up linking CCT2 to mRNA decay
   • Shown in P. yoelii, not P. falciparum
4. 2022 Low

   To define the composition and clients of the parasite CCT chaperonin, the complex was purified and its subunits and interactors catalogued, confirming CCT2 as a bona fide subunit.

   Evidence FLAG-tag affinity purification (via SLI) of CCT8-purified PfCCT complexes and mass spectrometry of synchronized trophozoites in P. falciparum

   PMID:36567946

   Open questions at the time

   • Single affinity-purification/MS study establishing membership only
   • No direct functional experiment on the CCT2 subunit
   • Client engagement (actin, tubulin, WD40 proteins) ascribed to the complex, not CCT2

• What CCT2/PF3D7_0306800 contributes to the PfCCT/TRiC complex beyond membership — its individual essentiality, substrate specificity, and any subunit-specific function — remains uncharacterized.
• No CCT2-specific loss-of-function or rescue experiment
• No structural model of the CCT2 subunit within PfCCT
• No demonstration that CCT2 selects any particular client