COQ8 (ABC1/YGL119W, UniProt P27697) – review notes

Role in CoQ biosynthesis

• COQ8 = ABC1; null mutants lack Q and accumulate HHB PMID:11279158; mitochondrial, processed on import PMID:11279158.
• Peripheral protein on the matrix side of the inner membrane PMID:21296186; PMID:18801050.
• Overexpression stabilizes the CoQ synthome in coq null mutants (PMID:24406904, PMID:22593570).
• Coq3/Coq5/Coq7 phosphorylation depends on Coq8 PMID:21296186 – historically interpreted as Coq8 being a protein kinase.

Biochemistry (supersedes the protein-kinase model)

• PMID:27499294.
• PMID:27499294.
• Purified Coq8 (NΔ41) autophosphorylates only in cis; autophosphorylation sites are dispensable in vivo PMID:27499294.
• ADP-selective nucleotide pocket; A-rich loop A-to-G mutation enables autophosphorylation but impairs CoQ biosynthesis (ADCK3 paper PMID:25498144, with in vivo Coq8p structure-function tests).

GO implications

• protein kinase activity (IMP, PMID:22593570) is contradicted by direct in vitro assays (PMID:27499294) and by UniProt's NOT annotation -> REMOVE.
• Core MF: ATP hydrolysis activity (GO:0016887) + lipid binding (GO:0008289), acting on the matrix face of the inner membrane in CoQ biosynthesis. The module deliberately asserts no MF for Coq8; this review accepts ATPase and lipid binding as the experimentally demonstrated activities, while how they drive CoQ synthesis remains unresolved.
• COQ8 is absent from YeastCyc pathways (no reactions in the summary file).
• PomBase GO-CAM 662af8fa00000408 types S. pombe coq8 with GO:0004672 protein kinase activity (positively regulating coq3) – disagrees with PMID:27499294.

Audit to COMPLETE (2026-11-11)

• Deep research: no provider deep-research file is available (no API keys in this session).
• kinase activity (GO:0016301, IDA PMID:27499294) changed from KEEP_AS_NON_CORE to MARK_AS_OVER_ANNOTATED:
  the activity is in-cis autophosphorylation whose sites are dispensable in vivo
  PMID:27499294,
  so it is in vitro activity that does not reflect function.
• Added NEW GO:0031314 extrinsic component of mitochondrial inner membrane (IDA PMID:21296186) and used it
  as the core-function location.
• Module note: the module asserts no MF for the Coq8 annoton; this review keeps ATP hydrolysis and lipid
  binding as experimentally demonstrated activities.