# ATP6V1B1 (V-type proton ATPase subunit B, kidney isoform; VATB1_HUMAN, P15313) ## Summary ATP6V1B1 encodes the B1 (kidney/tissue-restricted) isoform of the non-catalytic B subunit of the V1 peripheral domain of the vacuolar H+-ATPase (V-ATPase). The V1 domain hydrolyzes ATP, and this chemical energy drives proton translocation through the membrane-embedded V0 domain, acidifying intracellular compartments and, in specialized cells, the extracellular space. ## Core identity and function - Non-catalytic V1 subunit: "Non-catalytic subunit of the V1 complex of vacuolar(H+)- ATPase (V-ATPase), a multisubunit enzyme composed of a peripheral complex (V1) that hydrolyzes ATP and a membrane integral complex (V0) that translocates protons" [UniProt P15313 FUNCTION, "Non-catalytic subunit of the V1 complex of vacuolar(H+)-ATPase"]. - The B subunits form three AB catalytic heterodimers that constitute the V1 heterohexamer: "The V1 complex consists of three catalytic AB heterodimers that form a heterohexamer" [UniProt P15313 SUBUNIT]. B subunits hold non-catalytic nucleotide (ATP) sites; UniProt annotates an ATP-binding residue at position 394 (by similarity to P21281) [UniProt P15313 FT BINDING 394 "ligand=ATP"]. - Essential for assembly/activity: "Essential for the proper assembly and activity of V-ATPase" [UniProt P15313 FUNCTION]. - Renal proton secretion: "In renal intercalated cells, mediates secretion of protons (H+) into the urine thereby ensuring correct urinary acidification" [UniProt P15313 FUNCTION]. ## Structural / complex membership (V1 domain) - Cryo-EM of complete human V-ATPase places B subunits in the V1 ATP-hydrolytic head: "V-ATPases ... comprised of a cytoplasmic V1 complex for ATP hydrolysis and a membrane-embedded Vo complex for proton transfer... The V1 ATPase is composed of three copies of subunits A, B, E, and G, and one copy of subunit C, D, F, and H" [PMID:33065002 "The V 1 ATPase is composed of three copies of subunits A, B, E, and G"]. This is the IDA support for GO:0000221 (V-ATPase V1 domain). ## Disease and physiology - Loss-of-function mutations cause autosomal recessive distal renal tubular acidosis with sensorineural deafness (DRTA2): "mutations in ATP6B1, encoding the B-subunit of the apical proton pump mediating distal nephron acid secretion, cause distal renal tubular acidosis... Patients with ATP6B1 mutations also have sensorineural hearing loss; consistent with this finding, we demonstrate expression of ATP6B1 in cochlea and endolymphatic sac" [PMID:9916796]. - Mechanism of disease variants — assembly and apical trafficking defects: "GFP-B1WT formed complexes with other H+ -ATPase subunits (c, H, and E), whereas GFP-B1M did not. Proteins that were immunoprecipitated... from GFP-B1WT cells had ATPase activity, whereas proteins from GFP-B1M cells did not. Proton pump-mediated intracellular pH transport was inhibited in GFP-B1M-transfected cells... B1 point mutations prevent normal assembly of the H+ -ATPase and also may act as an inhibitor of H+ -ATPase function by competing with endogenous intact H+ -ATPase for trafficking" [PMID:16769747]. This grounds: V-ATPase complex assembly (GO:0070072), proton transmembrane transport (GO:1902600), pH reduction (GO:0045851), apical plasma membrane localization (GO:0016324). - Renal acid secretion / urinary acidification (regulation of pH, renal tubular secretion): "Defects in the B1 subunit gene ATP6V1B1... cause rdRTA with deafness... apical H(+)-ATPase that cause rdRTA" [PMID:12414817]. - Hearing: clinical genetic studies link ATP6V1B1 mutations to early-onset sensorineural hearing loss and enlarged vestibular aqueduct (EVA): "Mutations in ATP6V1B1 are associated with early onset SNHL... confirms the association of EVA and mutations in the ATP6V1B1 gene" [PMID:19639346]; "a significant percentage of the children with DRTA had sensorineural hearing loss and mutation in ATP6V1B1 gene" [PMID:20622307]. ## Localization / tissue specificity - Apical membrane in kidney intercalated cells and early distal nephron (TAL, DCT): "the B1 subunit is expressed in the apical membrane domains of TAL, macula densa, and DCT in human and rodent kidney. Furthermore, by immunoelectron microscopy the subunit is localized to the apical plasma membrane in the DCT" [PMID:29993276]. Apical localization also documented in [PMID:16769747] ("GFP-B1WT and GFP-B1M are present in the apical membrane"). - Tissue-restricted: kidney/testis (mouse) and cochlea/endolymphatic sac; murine ortholog 93% identical: "Northern blotting detects a 2.2-kb Atp6v1b1 transcript in the kidney and testis, but not other major organs. In mouse kidney, the B1-subunit localizes to intercalated cells" [PMID:14585495]. The human ISS localization annotations (cytoplasm, microvillus, basolateral/lateral membrane) are transferred from this mouse ortholog (Q91YH6). - HPA: "Group enriched (kidney, salivary gland)" [UniProt P15313 DR HPA]. ## PDZ interactions / apical targeting - C-terminal PDZ-binding motif (residues 510–513) mediates interaction with NHERF1 and the bicarbonate transporter SLC4A7/NBC3: "The PDZ-binding motif mediates interactions with NHERF1 and SCL4A7" [UniProt P15313 DOMAIN]; "Forms a complex with NHERF1 and SCL4A7" [UniProt P15313 SUBUNIT]. Mutagenesis L513G abolishes these interactions [UniProt P15313 FT MUTAGEN 513]. (Primary ref PubMed:12444018 not cached locally; the interaction is documented in the UniProt record.) ## Notes on weaker / peripheral annotations - GO:0005515 protein binding (IPI, PMID:32814053): bare "protein binding" from a large-scale neurodegeneration interactome screen (IntAct pairwise hits with ATXN1, TARDBP, WFS1, HSPB1, etc.). Uninformative for molecular function; the biologically meaningful binding (PDZ→NHERF1/SLC4A7, AB hexamer assembly) is captured by complex membership and domain annotations. - GO:0070062 extracellular exosome (HDA; PMID:23533145, PMID:19199708, PMID:19056867): proteomic detection in urinary/parotid/prostatic-secretion exosomes; consistent with V-ATPase delivery to/recycling from the apical plasma membrane but a bystander localization, not a core function. - GO:0016241 regulation of macroautophagy (NAS, PMID:22982048): the cited paper is about lipofuscin formation in senescent fibroblasts being independent of macroautophagy/lysosomal activity; weak NAS link, V-ATPase-driven lysosomal acidification supports autophagy generally but this is a generic V-ATPase property, not specific to the B1 subunit. Non-core at best. - GO:0001503 ossification (IMP, PMID:16433694): the cited paper is a clinical genetics study of dRTA/deafness families (rickets noted as a downstream consequence of acidosis); not direct evidence that B1 functions in ossification. Over-annotation / indirect. - GO:0055074 calcium ion homeostasis (IMP, PMID:20622307): the cited paper is a hearing-loss clinical correlation report; no direct calcium-homeostasis experiment. Likely downstream/indirect (urinary calcium handling in dRTA). - GO:0016928804 (PMID:16928804): apical plasma membrane IDA — this paper is about RhCG ammonia transporter; H+-ATPase used only as a co-localization marker. Localization consistent but weak primary evidence for B1 specifically. - Various IEA Ensembl orthology transfers (synaptic vesicle lumen acidification, extrinsic component of synaptic vesicle membrane, adult behavior, olfactory behavior, chloride/potassium/sodium homeostasis, prostaglandin metabolism, etc.) derive from rodent orthologs and broad V-ATPase biology; the B1 isoform is kidney/inner-ear/ epididymis restricted, so neuronal synaptic-vesicle roles are properties of other B isoforms (B2) rather than B1. Treat as non-core / over-annotation. - Reactome cytosol (TAS) annotations: generic "cytosol" placement for V1 subunits in many Reactome pathways; the V1 domain is cytoplasmic, so cytosol is acceptable but low-information and largely redundant. ## Falcon deep research synthesis (2026-06-21) Falcon deep research has now completed (`file:human/ATP6V1B1/ATP6V1B1-deep-research-falcon.md`, 17 citations). It corroborates the B1 (kidney-isoform, non-catalytic V1 subunit) biology above and adds one mechanistically specific finding. - **Core confirmed.** B1 is a non-catalytic V1 subunit forming the AB heterodimers of the V1 hexamer; the proton gradient it helps generate (via catalytic A subunit) acidifies organelles and, in renal type-A intercalated cells, secretes H+ into urine. No change to the non-catalytic-subunit / acidification calls. - **New: chemiosmotic coupling to cystinosin (Jamalpoor 2020).** In CRISPR ATP6V1B1-deficient human proximal tubule cells, loss of B1 disrupts coupling between the V-ATPase proton gradient and **cystinosin (CTNS, H+/cystine symporter)**, causing ~3-fold lysosomal **cystine accumulation** (normalized by cysteamine) and ~3-fold increased nuclear **TFEB** (autophagy/lysosomal biogenesis). This extends B1's relevance to proximal-tubule lysosomal physiology and mechanistically links V-ATPase activity to lysosomal amino-acid efflux — good support for the lysosomal-acidification role and the autophagy/mTORC1-TFEB connection (downstream, non-core). - **Disease.** Biallelic variants → autosomal-recessive **distal renal tubular acidosis** with the **strongest sensorineural-hearing-loss association** among dRTA genes (9/9 patients; 67% with large vestibular aqueduct syndrome; Ay 2023), reflecting V-ATPase maintenance of endolymph composition. Consistent with the established kidney/inner-ear core. Net: no change to calls — B1 is the kidney/inner-ear-restricted non-catalytic V1 subunit supporting organellar and renal-luminal acidification.