CCT6

CCT6 (PF3D7_0608700) is a subunit of the cytosolic TRiC/CCT chaperonin complex of Plasmodium falciparum, characterized in the available corpus only through its membership in that complex rather than through any activity attributable to CCT6 alone (PMID:28067475, PMID:36567946). The CCT6-containing PfCCT complex, purified from trophozoite-stage parasites, co-purifies with actin, tubulin, WD40-domain proteins, and translation initiation factors including eIF2α, consistent with a role in folding these cytosolic substrates (PMID:36567946). The complex resides in the parasite cytosol and is not exported into the host red blood cell, and regulatable knockdown of a sibling TRiC subunit causes severe asexual growth defects without altering protein export, establishing that the complex is essential for parasite growth and functions within the parasite (PMID:28067475). Sequence alignment shows that CCT6 carries a conservative substitution in the conserved ATP-hydrolysis motif (GDGSS in place of GDGTT) while retaining the flanking catalytic aspartates, a feature that may contribute to heterogeneity in the complex's sequential ATP-hydrolysis cycle (PMID:26443825). Beyond its role as a complex subunit, no CCT6-specific molecular function, substrate, or loss-of-function phenotype has been directly characterized in the available corpus; findings regarding TRiC substrate binding and any association with translational regulatory machinery apply to the complex, not to CCT6 individually (PMID:30703164, PMID:25615740).

1. 2015 Low

   Establishing that CCT6 is an authentic subunit of the native parasite chaperonin and noting its divergent catalytic motif framed CCT6 as a potentially specialized component of the sequential ATPase cycle.

   Evidence Multiple sequence alignment of all PfCCT subunits identifying the GDGSS-for-GDGTT substitution in CCT6

   PMID:26443825

   Open questions at the time

   • Sequence analysis only; no in vitro biochemical validation of CCT6 ATPase activity
   • Functional consequence of the GDGSS motif untested
   • Contribution of CCT6 to complex assembly not addressed
2. 2015 Low

   An early proposal implicated the PfTRiC complex in chaperoning exported Maurer's cleft proteins, raising the possibility that the chaperonin acts in host-cell protein trafficking.

   Evidence Co-immunoprecipitation and N-terminal domain mapping of PfSBP1 with PfTRiC in infected erythrocytes

   PMID:25615740

   Open questions at the time

   • CCT6's individual contribution not distinguished from the complex
   • Subsequently contradicted regarding TRiC export role
   • No functional demonstration of CCT6 in export
3. 2017 Medium

   Determining the localization and essentiality of the TRiC complex resolved where it acts, showing it functions inside the parasite cytosol and is required for asexual growth rather than for host-cell protein export.

   Evidence Epitope-tagged transgenic lines, parasite-specific antibody localization, and regulatable knockdown of a sibling TRiC subunit with growth and export readouts

   PMID:28067475

   Open questions at the time

   • Phenotype demonstrated by knockdown of a sibling subunit, not CCT6 itself
   • CCT6 membership inferred from complex studies
   • Single lab
4. 2019 Low

   Detection of the TRiC complex among interactors of the CCR4/NOT deadenylase machinery hinted at a link between the chaperonin and translational/stress-granule regulation.

   Evidence GFP-tagged PyCCR4-1 co-immunoprecipitation with mass spectrometry and SAINT scoring in P. yoelii schizonts

   PMID:30703164

   Open questions at the time

   • CCT6 detected only at a sub-threshold SAINT score
   • No functional follow-up on CCT6
   • Interaction shown in P. yoelii, not P. falciparum
5. 2022 Medium

   Native purification of the intact complex defined its substrate repertoire, identifying actin, tubulin, WD40-domain proteins, and initiation factors including eIF2α as PfCCT clients.

   Evidence FLAG-SLI affinity purification via CCT8 followed by proteomics from synchronized trophozoites

   PMID:36567946

   Open questions at the time

   • Substrates attributed to the complex, not to CCT6 specifically
   • No direct folding assay for any client
   • Single lab, no independent replication

• Whether CCT6 has any function, substrate specificity, or catalytic contribution distinct from its role as a complex subunit remains unknown.
• No CCT6-specific knockdown or knockout phenotype
• GDGSS motif function untested biochemically
• No structural model of CCT6 within the parasite complex