ccmC (P0ABM1, b2199) notes

Provenance / process

• 2026-10-23: Deep research could not be run. just deep-research-falcon ECOLI ccmC
  failed with Exception: Failed to authenticate, and no other provider credentials
  were available. This review is based on the cached publications cited in GOA and in
  the system I module (modules/bacterial_cytochrome_c_maturation_system_i.yaml), the
  UniProt record, and the reviewed P. putida ortholog (genes/PSEPK/ccmC).

Biology

• Six-TM inner-membrane protein, CcmC/CycZ/HelC family (heme-handling protein
  superfamily with the WWD motif). PMID:10998170
• Only Ccm protein strictly required for holo-CcmE formation; works without CcmAB when
  overexpressed. PMID:10339610
• Binds heme directly. PMID:11384983
• His60/His184 are the heme axial ligands in the purified CcmCDE complex.
  PMID:19629033
• WWD domain binds heme and orients the 2-vinyl for attachment to CcmE His130.
  PMID:29518410
• Holo-CcmE stays trapped on CcmC without CcmAB; ATP-dependent release from CcmA2B1C1.
  PMID:16824107
• Heme export by CcmABC is not established.
  PMID:24044352
  PMID:10708391

Curation decisions (summary)

• Core: heme binding (GO:0020037), protein-heme linkage (GO:0017003, heme onto CcmE),
  cytochrome c biosynthetic process (GO:1903607), plasma membrane.
• Catalase activity IBA (single P. aeruginosa CcmC IMP donor, Q9I3N5) and the derived
  oxidant-detoxification IEA removed: mutant phenotype, not CcmC catalysis.
• Heme transmembrane transporter / heme transport IEA marked over-annotated (not REMOVE:
  route of heme to the periplasmic WWD domain is unresolved). Heme import across plasma
  membrane NAS removed (wrong direction, contradicted by the cited paper).
• ABC transporter complex NAS kept as non-core (complex membership real, transport not shown).
• Nine bare protein-binding IPI rows removed per policy (interactions with CcmA, CcmD,
  CcmE are real).

2026-11-06 system I comparative reassessment

Binds heme in the periplasmic WWD site and positions it for covalent loading onto the CcmE chaperone. The E. coli evidence is distinguished from heterologous ortholog assays and engineered expression constructs.

Read the full 2023 E. coli structures (PMID:37626034), 2025 CcmB efflux work (PMID:40026579) and CcmCD crosslink mapping (PMID:40167305). The studies disagree about the heme conduit. ATP-dependent holo-CcmE release and covalent loading remain supported; heme contact, engineered overexpression, and proposed channel models are distinguished from purified vectorial transport. Broad intracellular heme handoff is not equivalent to membrane translocation. The 2025 review PMID:40460019 is abstract-only and is not used to settle this disagreement.

Specific reassessment: Binds heme in the periplasmic WWD site and positions it for covalent loading onto the CcmE chaperone.

Catalase source PMID:18174132 is abstract-only; publisher full-text endpoint returned403. Its explicit loss-of-catalase-production phenotype does not establish intrinsic CcmC catalase. Catalase and dependent oxidant-detoxification rows are UNDECIDED, without donor-count or invented negative-assay arguments.

Default Falcon was genuinely attempted and failed with HTTP403 authentication; no provider report was created. Manual literature assessment is recorded here. Original seed rows (including inherited NEW), raw UniProt/GOA, and existing provider files are preserved against original-members-baseline.json. Focused validation and helper history are recorded in the original-panel audit ledger.

2026-11-06: PR6121 round-2 location-evidence audit

Replaced chemistry-only support on location rows 16 and added matching locational evidence to location-bearing cores. CcmC has experimentally supported integral membrane topology with six helices. This supports the inner-membrane location independently of heme-ligand chemistry. Annotation actions and every original non-review payload, including historical NEW rows, remain unchanged. Full prior reviews and source hashes were frozen before editing in the round2-location cache; the durable preservation proof records comparison to published head 044f9278bcea364ad66bccc221fdfc78132ba4eb.