# ATP23 review notes

Review date: 2026-06-03.

Falcon deep research was requested for the Proteostasis PN review. The command `just deep-research-falcon human ATP23 --fallback perplexity-lite` produced `ATP23-deep-research-falcon.md` and one Falcon artifact, but the wrapper returned nonzero after a 600 second Falcon timeout and the configured `perplexity-lite` fallback failed with a Perplexity quota 401. The Falcon file was still usable and was reviewed together with UniProt, GOA, cached publications, PANTHER/InterPro, and the PN projection reports.

Core biology: human ATP23/Q9Y6H3 is a conserved ATP23-family M76 metalloprotease homolog. The best mechanistic evidence is from yeast ATP23/Atp23. Zeng et al. identify a nuclear ATP23 metalloprotease required for mitochondrial ATPase expression: [PMID:17135290 The metalloprotease encoded by ATP23 has a dual function in processing and assembly of subunit 6 of mitochondrial ATPase., "Mutations in ATP23 cause the accumulation of the precursor form of subunit 6 and prevent assembly of F O ."] They further show processing plus a separate assembly role: [PMID:17135290, "Atp23p, in addition to its processing activity, must provide another important function in F O assembly"] and describe the topology as mitochondrial inner membrane with IMS exposure: [PMID:17135290, "Atp23p is associated with the inner membrane in an orientation such that the C-terminus faces the intermembrane space."] Osman et al. independently summarize the dual function as an IMS peptidase/chaperone for ATP synthase: [PMID:17135288 Prohibitins interact genetically with Atp23, a novel processing peptidase and chaperone for the F1Fo-ATP synthase., "conserved metallopeptidase present in the intermembrane space, termed Atp23"] and [PMID:17135288, "Atp23 promotes the association of mature Atp6 with Atp9 oligomers"].

Human evidence is stronger for mitochondrial context than for direct substrate. He et al. define the human ATP synthase membrane-domain assembly pathway and ATP6/ATP8 insertion context: [PMID:29440398 Assembly of the membrane domain of ATP synthase in human mitochondria., "This intermediate provides the template for insertion of ATP6 and ATP8"]. The human MitoCoP study supports ATP23 as part of a high-confidence mitochondrial proteome, but not a specific submitochondrial topology for ATP23: [PMID:34800366 Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context., "We defined a human mitochondrial high-confidence proteome (MitoCoP) of 1,134 protein-coding genes"]. UniProt records the M76 family/domain and InterPro2GO metalloendopeptidase mapping: [file:human/ATP23/ATP23-uniprot.txt, "InterPro; IPR019165; Peptidase_M76_ATP23."].

PN projection review: ATP23 is listed in the PN intermembrane-space-protease bucket with candidate GO:0005758; this is acceptable as a conservative, compartmental location only when supported by ATP23 family topology evidence.

PN projection review: the projected GO:0035694 mitochondrial protein catabolic process should not be propagated for ATP23 in this review, because the strongest evidence supports ATP synthase assembly and Atp6 processing rather than a demonstrated human mitochondrial protein catabolic-process role.

The 2024 alpha-synuclein paper gives indirect yeast proteostasis context, not a direct human ATP23 annotation basis: [PMID:38906862 Enhancing mitochondrial proteolysis alleviates alpha-synuclein-mediated cellular toxicity., "Atp23 proteases showed the highest inhibitory effects on alpha-Syn accumulation in mitochondria"].

The historical KUB3/XRCC6BP1 DNA-repair annotations should be treated cautiously. The original KUB paper describes Ku70-binding proteins and says [PMID:10219089 Isolation of Ku70-binding proteins (KUBs)., "We isolated Ku70-binding proteins (KUB1-KUB4) using yeast two-hybrid analyses."] It does not establish ATP23/KUB3 as a DNA-dependent protein kinase, a DNA-PK-DNA ligase IV complex member, or an NHEJ effector. Falcon also explicitly cautions that KUB3/XRCC6BP1 DNA-repair literature should be separated from robust mitochondrial Atp23 ortholog biology until identifier/function mapping is confirmed.