# ATP6V0A4 Gene Review Notes

## 2026-06-03 - Proteostasis PN review

`just fetch-gene human ATP6V0A4` created the local scaffold, UniProt record, GOA table, publication cache, and PANTHER family data. GOA seeded 47 review rows, dominated by V-ATPase complex/V0-domain membership, proton transport and acidification, kidney apical membrane localization, endosomal/lysosomal/exosome locations, and broad binding rows.

Falcon deep research has now completed successfully (`ATP6V0A4-deep-research-falcon.md`, 22 citations); see the synthesis section at the end of this file. The original PN-batch attempt timed out before the `deep_research_unified` tool bugs were fixed. The review used the local UniProt record, GOA, cached publications, Reactome records, and PN projection files, now supplemented by the Falcon report.

Core functional synthesis: ATP6V0A4 encodes the a4 isoform of the V-ATPase V0 a subunit. It is a membrane-integral V0-sector component that contributes to the assembled V-ATPase rotational proton-pump activity, especially in kidney proton-secreting cells. Human disease and localization evidence support apical plasma membrane targeting in renal intercalated cells and a role in vectorial acid transport into urine [PMID:10973252, "vectorial proton transport is required for urinary acidification"; PMID:10973252, "essential role in normal vectorial acid transport into the urine by the kidney"]. ATP6V0A4 is also expressed in the cochlea, and ATP6V0A4 mutations can be associated with later-onset hearing loss [PMID:12414817, "several patients with ATP6V0A4 mutations have developed hearing loss"; PMID:12414817, "show ATP6V0A4 expression within the cochlea for the first time"].

Subunit-coupling evidence supports retaining V-ATPase/V0-domain and ATPase-binding annotations. The a4 subunit interacts with V1-sector G subunits, supporting V1/V0 coupling [PMID:17360703, "a4 and G3 are component subunits of the same proton pump"]. Disease-variant and yeast rescue experiments support a functional role for a4/PFK-1 interaction in proton-pump coupling rather than generic protein binding [PMID:18632794, "PFK-1 in normal proton pump function"].

Structural support: the current UniProt record lists human V-ATPase structures that include ATP6V0A4, including PDB:9DET and PDB:7UNF [file:human/ATP6V0A4/ATP6V0A4-uniprot.txt, "PDB; 9DET"]. These are useful future support for V0-domain structural annotations, but they do not by themselves resolve the PN lysosomal-specific projection question.

Generic `GO:0005515 protein binding` rows were marked over-annotated. The PFK-1 and V-ATPase subunit interactions are real, but generic protein binding is less informative than V-ATPase complex membership, ATPase binding, and proton-pump coupling. The high-throughput APOE interaction row from the neurodegenerative-disease interactome was also treated as non-core/uninformative [PMID:32814053, "generated by systematic yeast two-hybrid interaction screening"].

PN curation conclusion: the PN projection lists ATP6V0A4 as a candidate for `GO:0007042 lysosomal lumen acidification` and `GO:0046610 lysosomal proton-transporting V-type ATPase, V0 domain` under the autophagy-lysosome pathway [file:projects/PROTEOSTASIS/reports/pn_projection/pn_projected_candidate_additions.tsv, "ATP6V0A4"]. This is plausible at the generic V-ATPase-family level, but conservative gene-level review does not justify adding either projection as a new ATP6V0A4 core annotation. Existing evidence supports broad `GO:0007035 vacuolar acidification`, V0-domain membership, and a high-throughput `GO:0005765 lysosomal membrane` row, but the best ATP6V0A4-specific human biology is renal apical plasma membrane acid secretion rather than direct lysosomal lumen acidification. The YAML keeps the lysosomal membrane row as non-core and records a suggested expert question about whether the PN lysosomal projection should be applied to a4 or restricted to better-supported lysosomal a-subunit contexts.

Several vesicle-location annotations were retained cautiously or marked over-annotated. Endosome/endosome membrane rows are kept as non-core because Reactome and V-ATPase biology support endosomal acidification generally, but they are less ATP6V0A4-specific than the renal membrane literature. Synaptic-vesicle and phagocytic-vesicle projections were marked over-annotated because they over-specify a4 isoform localization from broad V-ATPase/orthology contexts.

## Falcon deep research synthesis (2026-06-21)

The Falcon report (`file:human/ATP6V0A4/ATP6V0A4-deep-research-falcon.md`) strongly
supports the gene-level conclusion above: the **best-supported a4-specific biology
is renal/cochlear apical-membrane H+ secretion, not lysosomal-lumen
acidification**, so the PN lysosomal projection (`GO:0007042`, `GO:0046610`) stays
unaccepted for a4 and the lysosomal-membrane row stays non-core.

**New gain-of-function evidence pins a4 to proton-pump capacity (Peng et al.
2025).** The first GOF variant, **p.V512L**, causes the mirror-image phenotype of
classic dRTA — hypochloremic metabolic **alkalosis with acidic urine**,
hypokalemia, renal insufficiency and hearing loss. V512 (conserved, C-terminal
TM) stabilizes a4 against degradation; V512L raises a4 abundance → more V-ATPase →
**excessive luminal H+ secretion**. Together with the many loss-of-function dRTA
variants, this bidirectional genetics directly ties ATP6V0A4 dosage to vectorial
proton transport, reinforcing the core renal acid-secretion MF/BP calls.

**Corroborated (no change to calls):** a4 isoform of the V0 a-subunit forming the
proton-conduction path (same arginine/c-ring-glutamate mechanism as a1); apical
plasma membrane of renal α-intercalated cells; expression in cochlea;
loss-of-function → distal renal tubular acidosis ± sensorineural hearing loss;
V1/V0 coupling via G-subunit interaction. A reported ccRCC downregulation/
prognostic-biomarker association (Xu 2023) is non-core. Net: no change to the
core call; renal apical acid secretion remains the a4-specific core, lysosomal
projection remains over-specified.