CCDC47

CCDC47 is an ER-resident transmembrane protein that functions as an obligate subunit of the PAT intramembrane chaperone complex (with Asterix/WDR83OS) and as a gating component of the multipass translocon, directing the biogenesis and folding of multi-spanning membrane proteins. Within the translocon, CCDC47 occludes the Sec61 lateral gate and redirects nascent transmembrane domains into a lipid-filled cavity behind Sec61, where they accumulate and fold; it similarly gates substrate access in the SND3 translocon pathway (PMID:32820719, PMID:36261528, PMID:41162385). CCDC47 also participates in ER-associated degradation through interactions with p97, BiP, and Derlins, and its loss impairs ERAD substrate dislocation and causes ER stress and embryonic lethality in mice (PMID:25009997). Bi-allelic loss-of-function variants in CCDC47 cause trichohepatoneurodevelopmental syndrome, associated with defective ER Ca²⁺ storage, IP3R-mediated release, and store-operated Ca²⁺ entry (PMID:30401460).

1. 2014 High

   The first mechanistic role for CCDC47 was established as an ERAD participant: its interaction with p97, BiP, and Derlins and the requirement for efficient degradation of misfolded substrates linked it to ER protein quality control, while knockout lethality demonstrated organismal essentiality.

   Evidence Co-immunoprecipitation of ERAD components, siRNA knockdown with ERAD substrate assays, and mouse knockout embryo analysis

   PMID:25009997

   Open questions at the time

   • Whether CCDC47 acts catalytically or as a scaffold in ERAD is unknown
   • The relationship between ERAD function and the later-discovered translocon role is unresolved
   • Mechanism of embryonic lethality beyond ER stress description is not defined
2. 2018 Medium

   Human genetics and functional cell biology established that CCDC47 loss-of-function causes trichohepatoneurodevelopmental syndrome and disrupts ER Ca²⁺ homeostasis, revealing a physiological role in Ca²⁺ storage and store-operated Ca²⁺ entry distinct from its translocon functions.

   Evidence Whole-exome sequencing of affected families, Ca²⁺ imaging in patient-derived cells

   PMID:30401460

   Open questions at the time

   • No reconstituted system demonstrates a direct Ca²⁺-regulatory mechanism for CCDC47
   • Whether Ca²⁺ defects are secondary to impaired biogenesis of Ca²⁺ channels/pumps is untested
   • Single-lab finding without independent replication
3. 2020 High

   Two concurrent studies resolved the molecular identity of the multipass translocon and the PAT complex: CCDC47 was shown to be a core component of a ~360 kDa ribosome-associated ER complex organized around a membrane cavity, and to form an obligate heterodimer with Asterix (WDR83OS) that chaperones unshielded hydrophilic residues within transmembrane domains of nascent multipass clients.

   Evidence Cryo-EM of the ribosome-translocon complex, reciprocal co-immunoprecipitation, loss-of-function proteomics showing reduced multipass client levels

   PMID:32814900 PMID:32820719

   Open questions at the time

   • How the PAT complex recognizes and selects specific polar residues within TMDs is structurally unresolved
   • The client repertoire beyond validated examples (e.g. EAAT1) is incompletely defined
   • Relationship between PAT complex function and the ERAD role remains unclear
4. 2022 High

   Structural trapping of translocation intermediates revealed the precise mechanism by which CCDC47 latches the Sec61 lateral gate closed, forcing nascent TMDs behind Sec61 into a semi-enclosed lipid-filled cavity where sequential TMDs accumulate and fold, establishing the architectural basis of multipass membrane protein insertion.

   Evidence Cryo-EM of biogenesis intermediates with pharmacological Sec61 lateral gate inhibitor validation

   PMID:36261528

   Open questions at the time

   • Dynamics of TMD release from the cavity into the lipid bilayer are not captured
   • Whether different multipass clients use the cavity identically is unknown
   • No high-resolution structure of the CCDC47–Asterix heterodimer alone exists
5. 2024 Medium

   Identification of disease-causing WDR83OS (Asterix) variants producing a phenocopy of CCDC47-linked trichohepatoneurodevelopmental syndrome confirmed that the intact PAT heterodimer is essential in vivo and that disruption of either subunit produces overlapping pathology.

   Evidence Exome sequencing across multiple unrelated families, zebrafish wdr83os loss-of-function model

   PMID:39471804

   Open questions at the time

   • The specific PAT-dependent clients whose loss underlies the disease phenotype are not identified
   • Whether residual CCDC47 function persists without Asterix is untested biochemically
6. 2025 High

   CCDC47 was found to gate substrate access within the SND3 translocon in addition to the Sec61-based multipass translocon, broadening its role to a shared gating factor across distinct ER insertion pathways; separately, interactions with SPCA2C, STIM1, and Orai1 provided a molecular framework for its role in store-operated Ca²⁺ entry.

   Evidence Cryo-EM of SND3 translocon with molecular dynamics simulations; BioID, co-IP, and Ca²⁺ imaging for SOCE pathway components

   PMID:40783819 PMID:41162385

   Open questions at the time

   • Whether CCDC47's gating role in SND3 and Sec61 translocons is regulated differentially is unknown
   • The SPCA2C–CCDC47 interaction awaits reconstitution and structural characterization
   • How CCDC47 partitions between translocon, ERAD, and Ca²⁺-regulatory complexes is undefined

• A unified model explaining how CCDC47 coordinates its roles in multipass translocon gating, intramembrane chaperoning, ERAD, and ER Ca²⁺ homeostasis — and whether these represent distinct pools or sequential functions — remains to be established.
• No study has addressed whether CCDC47's translocon and ERAD functions are mechanistically linked or independent
• The Ca²⁺ phenotype could be secondary to impaired biogenesis of Ca²⁺ handling proteins — direct versus indirect effects are unresolved
• Tissue-specific client repertoires and disease mechanisms remain uncharacterized