id: Q9UI12 gene_symbol: ATP6V1H product_type: PROTEIN status: COMPLETE taxon: id: NCBITaxon:9606 label: Homo sapiens description: >- ATP6V1H encodes V-type proton ATPase subunit H (483 amino acids, ~57 kDa), the regulatory subunit H of the V1 peripheral domain of the vacuolar-type H+-ATPase (V-ATPase). Subunit H is present as a single copy in the V1 complex and has a dual regulatory role: in the assembled V-ATPase holoenzyme it supports proton pump activity, while in the free cytosolic V1 complex (dissociated from V0 during regulated disassembly) it inhibits futile ATP hydrolysis. Beyond its structural role in the V-ATPase, subunit H directly binds to AP2M1 (the medium chain mu2 of adaptor protein complex 2) through armadillo repeat domains spanning residues 133-363, physically connecting the V-ATPase to the clathrin-mediated endocytic machinery. The protein was originally identified as Nef-binding protein 1 (NBP1) and is the human ortholog of yeast Vma13p. HIV-1 and SIV Nef exploit the subunit H-AP2M1 interaction to forcibly internalize CD4 from infected cell surfaces, but this reflects co-option of a normal cellular endocytic function. Two isoforms exist (Q9UI12-1 and Q9UI12-2); isoform 2 differs at residues 176-193. The protein localizes to lysosomal and endosomal membranes (as part of assembled V-ATPase), to the cytosol (as part of free V1 complex), and at clathrin-coated vesicle membranes. ATP6V1H is ubiquitously expressed. alternative_products: - name: '1' id: Q9UI12-1 - name: '2' id: Q9UI12-2 sequence_note: VSP_012274 existing_annotations: - term: id: GO:0000221 label: vacuolar proton-transporting V-type ATPase, V1 domain evidence_type: IBA original_reference_id: GO_REF:0000033 qualifier: part_of review: summary: Subunit H is a genuine V1 domain component confirmed by cryo-EM and biochemical characterization. action: ACCEPT reason: V1 domain membership is well established. Subunit H is a regulatory component of the V1 complex, one copy per holoenzyme (PMID:33065002, PMID:9442887). - term: id: GO:0007042 label: lysosomal lumen acidification evidence_type: IBA original_reference_id: GO_REF:0000033 qualifier: involved_in review: summary: IBA phylogenetic transfer; lysosomal acidification is the core biological output of the assembled V-ATPase containing subunit H. action: ACCEPT reason: Lysosomal lumen acidification is the primary downstream consequence of V-ATPase proton pumping. As a regulatory subunit essential for V-ATPase activity, H is rightly annotated as involved in this process. - term: id: GO:0097401 label: synaptic vesicle lumen acidification evidence_type: IBA original_reference_id: GO_REF:0000033 qualifier: involved_in review: summary: IBA transfer for synaptic vesicle lumen acidification; non-core neuronal context for this ubiquitously expressed subunit. action: KEEP_AS_NON_CORE reason: Neuronal synaptic vesicle acidification is a non-core context for this ubiquitous regulatory subunit. - term: id: GO:0000221 label: vacuolar proton-transporting V-type ATPase, V1 domain evidence_type: IEA original_reference_id: GO_REF:0000002 qualifier: part_of review: summary: IEA from InterPro; V1 domain membership is experimentally established. action: ACCEPT reason: V1 domain membership is supported by structural and functional data. - term: id: GO:0016020 label: membrane evidence_type: IEA original_reference_id: GO_REF:0000117 qualifier: located_in review: summary: IEA ARBA for membrane localization; overly general term but consistent with lysosomal/endosomal/plasma membrane localization. action: MODIFY reason: Generic membrane is too imprecise. The more specific terms lysosomal membrane (HDA), endosome membrane (NAS), and plasma membrane (NAS) already exist in the annotation set. The IDA annotation to GO:0016020 from PMID:33065002 directly contextualizes which membrane is meant. proposed_replacement_terms: - id: GO:0005765 label: lysosomal membrane - term: id: GO:0030665 label: clathrin-coated vesicle membrane evidence_type: IEA original_reference_id: GO_REF:0000044 qualifier: located_in review: summary: IEA from UniProt subcellular location mapping; consistent with the documented AP-2 (clathrin adaptor) interaction of subunit H. action: ACCEPT reason: Subunit H directly binds AP2M1 (PMID:12032142), which is a component of clathrin-coated vesicle machinery. Localization at clathrin-coated vesicle membrane is consistent with this interaction. supported_by: - reference_id: PMID:12032142 supporting_text: V1H binds to the C-terminal flexible loop in Nef from HIV-1 and to the medium chain (mu2) of the adaptor protein complex 2 (AP-2) in vitro and in vivo - term: id: GO:0046961 label: proton-transporting ATPase activity, rotational mechanism evidence_type: IEA original_reference_id: GO_REF:0000002 qualifier: enables review: summary: IEA from InterPro; proton-transporting ATPase rotational mechanism is the molecular activity of the V-ATPase complex. action: ACCEPT reason: The V-ATPase uses a rotational mechanism for proton translocation. Subunit H contributes to this complex activity as a regulatory component. - term: id: GO:1902600 label: proton transmembrane transport evidence_type: IEA original_reference_id: GO_REF:0000002 qualifier: involved_in review: summary: IEA from InterPro; proton transmembrane transport is the core biological process of the V-ATPase. action: ACCEPT reason: Proton transmembrane transport is the fundamental function of the V-ATPase complex. Subunit H is essential for this activity as a regulatory component. - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:32296183 qualifier: enables review: summary: Generic protein binding from binary interactome reference map; uninformative over-annotation. action: MARK_AS_OVER_ANNOTATED reason: High-throughput interactome dataset. The specific informative interaction is with AP2M1 (PMID:12032142), not the generic protein binding term. - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:32814053 qualifier: enables review: summary: Generic protein binding from neurodegenerative disease interactome; uninformative over-annotation. action: MARK_AS_OVER_ANNOTATED reason: High-throughput interactome dataset; protein binding does not describe specific molecular function of subunit H. - term: id: GO:0098850 label: extrinsic component of synaptic vesicle membrane evidence_type: IEA original_reference_id: GO_REF:0000107 qualifier: is_active_in review: summary: IEA Ensembl Compara transfer; non-core neuronal context for this ubiquitous subunit. action: KEEP_AS_NON_CORE reason: Synaptic vesicle context is non-core for this ubiquitously expressed regulatory subunit. - term: id: GO:0005829 label: cytosol evidence_type: IDA original_reference_id: GO_REF:0000052 qualifier: located_in review: summary: IDA from immunofluorescence curation; cytosolic localization reflects the free V1 complex state. action: KEEP_AS_NON_CORE reason: Cytosolic localization is a genuine functional state for subunit H. The free V1 complex is present in the cytosol when dissociated from V0, and subunit H specifically inhibits futile ATP hydrolysis in this context. - term: id: GO:0000139 label: Golgi membrane evidence_type: NAS original_reference_id: PMID:32001091 qualifier: located_in review: summary: NAS from V-ATPase review; Golgi membrane localization is mentioned for V-ATPase generally. Not specific to subunit H but consistent with the review's description of V-ATPase distribution. action: KEEP_AS_NON_CORE reason: Golgi membrane localization is supported only by NAS from a general V-ATPase review. While V-ATPase does localize to Golgi, this is not a core context for the H subunit. - term: id: GO:0005765 label: lysosomal membrane evidence_type: NAS original_reference_id: PMID:32001091 qualifier: located_in review: summary: NAS from V-ATPase review; lysosomal membrane localization is the core localization for the assembled V-ATPase holoenzyme. action: ACCEPT reason: Lysosomal membrane localization is well supported and is the primary localization of the assembled V-ATPase. Also supported by HDA mass spectrometry (PMID:17897319). - term: id: GO:0005886 label: plasma membrane evidence_type: NAS original_reference_id: PMID:32001091 qualifier: located_in review: summary: NAS from V-ATPase review; plasma membrane V-ATPase in specialized cell types (e.g., kidney intercalated cells). action: KEEP_AS_NON_CORE reason: Plasma membrane localization is a non-core context for this ubiquitous subunit; it occurs in specialized cells. The more relevant localization is lysosomal/endosomal. - term: id: GO:0007035 label: vacuolar acidification evidence_type: NAS original_reference_id: PMID:32001091 qualifier: involved_in review: summary: NAS from V-ATPase review; vacuolar acidification is the core biological process downstream of V-ATPase proton pumping. action: ACCEPT reason: Vacuolar acidification is the primary biological function of V-ATPase activity. Subunit H as a regulatory component of the V-ATPase is appropriately annotated to this process. - term: id: GO:0007042 label: lysosomal lumen acidification evidence_type: NAS original_reference_id: PMID:32001091 qualifier: involved_in review: summary: NAS from V-ATPase review; lysosomal lumen acidification is the core functional output of lysosome-localized V-ATPase. action: ACCEPT reason: Lysosomal lumen acidification is the primary biological process driven by the V-ATPase at the lysosomal membrane. Subunit H is a required regulatory component of this activity. - term: id: GO:0007042 label: lysosomal lumen acidification evidence_type: NAS original_reference_id: PMID:33065002 qualifier: involved_in review: summary: NAS from cryo-EM structure paper; lysosomal lumen acidification is the core function of the V-ATPase complex. action: ACCEPT reason: The structure paper describes V-ATPase function in intracellular acidification. Lysosomal lumen acidification is a core function. - term: id: GO:0010008 label: endosome membrane evidence_type: NAS original_reference_id: PMID:32001091 qualifier: located_in review: summary: NAS from V-ATPase review; endosome membrane localization of assembled V-ATPase is well established. action: ACCEPT reason: Endosomal membrane localization of V-ATPase is well established and important for receptor-mediated endocytosis and iron release from transferrin. - term: id: GO:0016020 label: membrane evidence_type: IDA original_reference_id: PMID:33065002 qualifier: located_in review: summary: IDA from cryo-EM structure study; this directly shows subunit H as part of the membrane-associated V-ATPase holoenzyme. action: MODIFY reason: The cryo-EM structure places subunit H in the V-ATPase complex at membranes. The generic membrane term is less informative than lysosomal membrane. Suggest retaining but noting more specific terms are preferred. proposed_replacement_terms: - id: GO:0005765 label: lysosomal membrane - term: id: GO:0033176 label: proton-transporting V-type ATPase complex evidence_type: NAS original_reference_id: PMID:33065002 qualifier: part_of review: summary: NAS from cryo-EM structure paper; V-ATPase complex membership is well established. action: ACCEPT reason: Subunit H is a confirmed component of the V-ATPase holoenzyme complex. - term: id: GO:0048388 label: endosomal lumen acidification evidence_type: NAS original_reference_id: PMID:32001091 qualifier: involved_in review: summary: NAS from V-ATPase review; endosomal lumen acidification is a core biological process downstream of V-ATPase activity at endosomes. action: ACCEPT reason: Endosomal acidification is required for receptor-mediated endocytosis completion and nutrient release. V-ATPase is the primary driver; subunit H is a required component. - term: id: GO:0051452 label: intracellular pH reduction evidence_type: NAS original_reference_id: PMID:32001091 qualifier: involved_in review: summary: NAS from V-ATPase review; intracellular pH reduction is a broader term encompassing all V-ATPase-dependent compartment acidification. action: KEEP_AS_NON_CORE reason: Intracellular pH reduction is a general consequence of V-ATPase activity. More specific annotations to lysosomal and endosomal lumen acidification are already present and are preferable. This broader term is non-core. - term: id: GO:0061795 label: Golgi lumen acidification evidence_type: NAS original_reference_id: PMID:32001091 qualifier: involved_in review: summary: NAS from V-ATPase review; Golgi lumen acidification is a downstream consequence of V-ATPase activity at Golgi membranes. action: KEEP_AS_NON_CORE reason: Golgi acidification is a non-core downstream function. Lysosomal and endosomal acidification are the primary core contexts. - term: id: GO:1902600 label: proton transmembrane transport evidence_type: NAS original_reference_id: PMID:33065002 qualifier: involved_in review: summary: NAS from cryo-EM structure paper; proton transmembrane transport is the core molecular function of the V-ATPase complex. action: ACCEPT reason: Proton transmembrane transport is the fundamental process of the V-ATPase. Subunit H is essential for this activity. - term: id: GO:0000221 label: vacuolar proton-transporting V-type ATPase, V1 domain evidence_type: ISS original_reference_id: GO_REF:0000024 qualifier: part_of review: summary: ISS manual ortholog transfer; V1 domain membership is experimentally established. action: ACCEPT reason: ISS consistent with direct experimental evidence for V1 domain membership. - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:25659576 qualifier: enables review: summary: IPI from TM9SF4/V-ATPase interaction study in colon cancer; TM9SF4 co-immunoprecipitates with ATP6V1H. This is a specific interaction study but the GO:0005515 annotation is still uninformative. action: MARK_AS_OVER_ANNOTATED reason: While TM9SF4 interaction with ATP6V1H is documented (PMID:25659576), the protein binding annotation is uninformative. The interaction is in a cancer cell context and the normal physiological relevance is unclear. - term: id: GO:0016241 label: regulation of macroautophagy evidence_type: NAS original_reference_id: PMID:22982048 qualifier: involved_in review: summary: NAS annotation; the cited paper uses V-ATPase disruption as a tool to impair lysosomal activity. Does not specifically implicate subunit H in macroautophagy regulation. action: MARK_AS_OVER_ANNOTATED reason: The cited study does not demonstrate that ATP6V1H specifically regulates macroautophagy; it uses generic V-ATPase disruption to block lysosomal function. This is an over-annotation of a generic downstream consequence of V-ATPase disruption. - term: id: GO:0070062 label: extracellular exosome evidence_type: HDA original_reference_id: PMID:19199708 qualifier: located_in review: summary: HDA from parotid gland exosome proteomics; likely a contaminant in exosome fractions. action: MARK_AS_OVER_ANNOTATED reason: Extracellular exosome identification in proteomics is likely contamination. Not a primary localization for a V1 peripheral complex subunit. - term: id: GO:0070062 label: extracellular exosome evidence_type: HDA original_reference_id: PMID:19056867 qualifier: located_in review: summary: HDA from urinary exosome proteomics; likely a contaminant in exosome fractions. action: MARK_AS_OVER_ANNOTATED reason: Extracellular exosome identification in proteomics is likely contamination. Not a primary localization for a V1 subunit. - term: id: GO:0005765 label: lysosomal membrane evidence_type: HDA original_reference_id: PMID:17897319 qualifier: located_in review: summary: HDA from lysosomal membrane proteomics; directly supports lysosomal membrane localization as part of the assembled V-ATPase. action: ACCEPT reason: Mass spectrometry in lysosome-enriched fractions directly identifies subunit H at the lysosomal membrane. supported_by: - reference_id: PMID:17897319 supporting_text: Integral and associated lysosomal membrane proteins - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-1222516 qualifier: located_in review: summary: Reactome TAS annotation; cytosolic localization reflects free V1 complex or V1H in its adaptor role during endocytic events. action: KEEP_AS_NON_CORE reason: Cytosolic localization is well-established for the free V1 complex. Subunit H has a specific regulatory role in the cytosolic free V1 state (inhibiting futile ATP hydrolysis). Multiple independent sources confirm this. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-167597 qualifier: located_in review: summary: Reactome TAS annotation for cytosol in Nef/CD4 endocytosis context; V1H bridges cytosolic Nef to the AP-2 endocytic complex. action: KEEP_AS_NON_CORE reason: In the Nef endocytosis pathway, V1H functions as a cytosolic adaptor. This is consistent with the documented AP2M1 binding. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-167601 qualifier: located_in review: summary: Reactome TAS annotation for cytosol in CD4 degradation pathway; consistent. action: KEEP_AS_NON_CORE reason: Cytosolic localization context; consistent with subunit H adaptor function. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-182171 qualifier: located_in review: summary: Reactome TAS annotation for cytosol in CD8 degradation pathway; consistent. action: KEEP_AS_NON_CORE reason: Cytosolic localization context; consistent with subunit H adaptor function. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-182198 qualifier: located_in review: summary: Reactome TAS annotation for cytosol in CD8 internalization; consistent. action: KEEP_AS_NON_CORE reason: Cytosolic localization context; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-5252133 qualifier: located_in review: summary: Reactome TAS annotation for cytosol; free V1 complex context. action: KEEP_AS_NON_CORE reason: Cytosolic localization of free V1 complex; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-74723 qualifier: located_in review: summary: Reactome TAS annotation for cytosol; free V1 complex context. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-917841 qualifier: located_in review: summary: Reactome TAS annotation for cytosol; free V1 complex context. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-9636397 qualifier: located_in review: summary: Reactome TAS annotation for cytosol; Mycobacterium PtpA binds ATP6V1H context. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent with free V1 complex. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-9639286 qualifier: located_in review: summary: Reactome TAS annotation for cytosol in mTORC1 signaling context. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-9640167 qualifier: located_in review: summary: Reactome TAS annotation for cytosol. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-9640168 qualifier: located_in review: summary: Reactome TAS annotation for cytosol. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-9640175 qualifier: located_in review: summary: Reactome TAS annotation for cytosol. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-9640195 qualifier: located_in review: summary: Reactome TAS annotation for cytosol. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-9645598 qualifier: located_in review: summary: Reactome TAS annotation for cytosol. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-9645608 qualifier: located_in review: summary: Reactome TAS annotation for cytosol. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-9646468 qualifier: located_in review: summary: Reactome TAS annotation for cytosol. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent. - term: id: GO:0005829 label: cytosol evidence_type: TAS original_reference_id: Reactome:R-HSA-9858916 qualifier: located_in review: summary: Reactome TAS annotation for cytosol. action: KEEP_AS_NON_CORE reason: Cytosolic localization; consistent. - term: id: GO:0005886 label: plasma membrane evidence_type: TAS original_reference_id: Reactome:R-HSA-167537 qualifier: located_in review: summary: Reactome TAS annotation for plasma membrane in Nef/CD4 complex context; V1H at plasma membrane bridges Nef to AP-2 for CD4 internalization. action: KEEP_AS_NON_CORE reason: Plasma membrane localization in the Nef/CD4 endocytosis context reflects the adaptor function but is non-core relative to lysosomal/endosomal localization. - term: id: GO:0005886 label: plasma membrane evidence_type: TAS original_reference_id: Reactome:R-HSA-167597 qualifier: located_in review: summary: Reactome TAS for plasma membrane in CD4 internalization context; non-core. action: KEEP_AS_NON_CORE reason: Non-core context; same reasoning as above. - term: id: GO:0005886 label: plasma membrane evidence_type: TAS original_reference_id: Reactome:R-HSA-182186 qualifier: located_in review: summary: Reactome TAS for plasma membrane in CD8/Nef complex context; non-core. action: KEEP_AS_NON_CORE reason: Non-core context; plasma membrane in Nef pathway. - term: id: GO:0005886 label: plasma membrane evidence_type: TAS original_reference_id: Reactome:R-HSA-182198 qualifier: located_in review: summary: Reactome TAS for plasma membrane in CD8 internalization context; non-core. action: KEEP_AS_NON_CORE reason: Non-core context. - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:11179428 qualifier: enables review: summary: IPI from SIV Nef/V-ATPase study; the specific interaction is SIV Nef with subunit H, exploiting the normal AP-2 adaptor function. The protein binding annotation is uninformative. action: MARK_AS_OVER_ANNOTATED reason: The SIV Nef-H interaction is documented (PMID:11179428) but the generic protein binding term does not capture the biology. The relevant specific function is the AP-2 medium chain (AP2M1) binding. - term: id: GO:0000221 label: vacuolar proton-transporting V-type ATPase, V1 domain evidence_type: NAS original_reference_id: PMID:9442887 qualifier: part_of review: summary: NAS from Stevens and Forgac review; V1 domain membership is well-established. action: ACCEPT reason: The 1997 Stevens and Forgac review is the foundational reference for V-ATPase V1 subunit composition including subunit H. supported_by: - reference_id: PMID:9442887 supporting_text: The peripheral V1 domain, a 500-kDa complex responsible for ATP hydrolysis, contains at least eight different subunits of molecular weight 70-13 (subunits A-H) - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:12032142 qualifier: enables review: summary: IPI from Geyer et al. 2002; this study demonstrated specific interaction with AP2M1. The protein binding annotation is uninformative but the underlying interaction is important. action: MARK_AS_OVER_ANNOTATED reason: The specific interaction with AP2M1 (mu2 adaptin) is meaningful and well-documented, but GO:0005515 protein binding is uninformative. A more specific annotation to AP-2 adaptor binding or clathrin adaptor binding would be more informative. - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:9620685 qualifier: enables review: summary: IPI from Lu et al. 1998; interaction with HIV-1 Nef documented. Generic protein binding is uninformative. action: MARK_AS_OVER_ANNOTATED reason: Generic protein binding annotation; the specific interaction is with HIV-1 Nef (a pathogen protein) and does not reflect normal cellular function. - term: id: GO:0006897 label: endocytosis evidence_type: IDA original_reference_id: PMID:12032142 qualifier: involved_in review: summary: IDA experimental evidence that V1H contributes to endocytosis via AP-2 interaction; this is a legitimate specific function of subunit H. action: ACCEPT reason: Geyer et al. 2002 demonstrated that V1H connects to the endocytic machinery through AP2M1 interaction, and V1H-Nef chimeras can drive CD4 internalization. This is genuine experimental evidence for H subunit involvement in clathrin-mediated endocytosis. supported_by: - reference_id: PMID:12032142 supporting_text: V1H can function as an adaptor for interactions between Nef and AP-2 - term: id: GO:0007035 label: vacuolar acidification evidence_type: NAS original_reference_id: PMID:9442887 qualifier: involved_in review: summary: NAS from foundational V-ATPase review; vacuolar acidification is the core biological process. action: ACCEPT reason: Vacuolar acidification is a core biological process driven by V-ATPase. The Stevens and Forgac review is a valid reference for this NAS annotation. supported_by: - reference_id: PMID:9442887 supporting_text: The vacuolar (H+)-ATPases (or V-ATPases) function in the acidification of intracellular compartments in eukaryotic cells - term: id: GO:0016887 label: ATP hydrolysis activity evidence_type: NAS original_reference_id: PMID:9442887 qualifier: contributes_to review: summary: NAS from foundational V-ATPase review; subunit H contributes to ATP hydrolysis activity of the V-ATPase complex. action: ACCEPT reason: ATP hydrolysis is the biochemical activity of the V1 domain. Subunit H is a regulatory component that modulates this activity. The contributes_to qualifier is appropriate. supported_by: - reference_id: PMID:9442887 supporting_text: The peripheral V1 domain, a 500-kDa complex responsible for ATP hydrolysis, contains at least eight different subunits of molecular weight 70-13 (subunits A-H) - term: id: GO:0030234 label: enzyme regulator activity evidence_type: NAS original_reference_id: PMID:9442887 qualifier: enables review: summary: NAS for enzyme regulator activity; subunit H is the regulatory H subunit that modulates V-ATPase ATP hydrolysis in assembled versus free V1 states. action: ACCEPT reason: Subunit H has a documented regulatory function — it inhibits futile ATP hydrolysis in the free V1 complex and activates the pump when assembled with V0. This enzyme regulator activity is a genuinely specific function of the H subunit distinguishing it from other V1 subunits. - term: id: GO:1902600 label: proton transmembrane transport evidence_type: NAS original_reference_id: PMID:9442887 qualifier: involved_in review: summary: NAS from foundational V-ATPase review; proton transmembrane transport is the core function. action: ACCEPT reason: Proton transmembrane transport is the core function of the V-ATPase. Subunit H as a regulatory component is appropriately annotated to this process. references: - id: GO_REF:0000002 title: Gene Ontology annotation through association of InterPro records with GO terms findings: [] - id: GO_REF:0000024 title: Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity findings: [] - id: GO_REF:0000033 title: Annotation inferences using phylogenetic trees findings: [] - id: GO_REF:0000044 title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt findings: [] - id: GO_REF:0000052 title: Gene Ontology annotation based on curation of immunofluorescence data findings: [] - id: GO_REF:0000107 title: Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara findings: [] - id: GO_REF:0000117 title: Electronic Gene Ontology annotations created by ARBA machine learning models findings: [] - id: PMID:11179428 title: Negative factor from SIV binds to the catalytic subunit of the V-ATPase to internalize CD4 and to increase viral infectivity. findings: - statement: SIV Nef binds subunit H of V-ATPase to contact endocytic machinery without direct AP-2 binding; subunit H plays important role in viral infectivity by connecting Nef to endocytic pathway. - id: PMID:12032142 title: Subunit H of the V-ATPase binds to the medium chain of adaptor protein complex 2 and connects Nef to the endocytic machinery. findings: - statement: >- V1H binds AP2M1 (mu2) through armadillo repeats 133-363; V1H functions as an adaptor connecting Nef to AP-2 and the endocytic machinery. - id: PMID:17897319 title: Integral and associated lysosomal membrane proteins. findings: - statement: Mass spectrometry identification of ATP6V1H in lysosome-enriched fractions supports lysosomal membrane localization. - id: PMID:19056867 title: Large-scale proteomics and phosphoproteomics of urinary exosomes. findings: - statement: Identification in urinary exosome fraction; likely contamination. - id: PMID:19199708 title: Proteomic analysis of human parotid gland exosomes by multidimensional protein identification technology (MudPIT). findings: - statement: Identification in parotid gland exosome fraction; likely contamination. - id: PMID:22982048 title: Lipofuscin is formed independently of macroautophagy and lysosomal activity in stress-induced prematurely senescent human fibroblasts. findings: - statement: V-ATPase disruption used as tool to impair lysosomal activity; does not demonstrate specific role of subunit H in macroautophagy regulation. - id: PMID:25659576 title: TM9SF4 is a novel V-ATPase-interacting protein that modulates tumor pH alterations associated with drug resistance and invasiveness of colon cancer cells. findings: - statement: TM9SF4 interacts with ATP6V1H in colon cancer cells; TM9SF4 suppression reduces V1/V0 assembly. - id: PMID:32001091 title: Structure and Roles of V-type ATPases. findings: - statement: >- V-ATPases are the primary source of organellar acidification; subunit isoforms are differentially localized; enzymatic activity modulated by regulated reversible disassembly. - id: PMID:32296183 title: A reference map of the human binary protein interactome. findings: [] - id: PMID:32814053 title: Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins and Uncovers Widespread Protein Aggregation in Affected Brains. findings: [] - id: PMID:33065002 title: Structures of a Complete Human V-ATPase Reveal Mechanisms of Its Assembly. findings: - statement: Cryo-EM structures of complete human V-ATPase; V1 complex contains regulatory subunits C and H; subunit H is part of the V1 peripheral domain. - id: PMID:9442887 title: Structure, function and regulation of the vacuolar (H+)-ATPase. findings: - statement: >- V1 domain contains eight subunits A-H; subunit H is the regulatory component; V-ATPase functions in acidification of intracellular compartments. - id: PMID:9620685 title: Interactions between HIV1 Nef and vacuolar ATPase facilitate the internalization of CD4. findings: - statement: NBP1 (subunit H) identified as Nef-binding protein; NBP1 is human homolog of yeast Vma13p; connects Nef to endocytic pathway. - id: Reactome:R-HSA-1222516 title: Intraphagosomal pH is lowered to 5 by V-ATPase findings: [] - id: Reactome:R-HSA-167537 title: Formation of CD4:Nef:AP-2 Complex:v-ATPase Complex findings: [] - id: Reactome:R-HSA-167597 title: Internalization of the CD4:Nef:AP-2 Complex:v-ATPase Complex findings: [] - id: Reactome:R-HSA-167601 title: Degradation of CD4 findings: [] - id: Reactome:R-HSA-182171 title: Degradation of CD8 findings: [] - id: Reactome:R-HSA-182186 title: Formation of CD8:Nef:AP-2 Complex:v-ATPase Complex findings: [] - id: Reactome:R-HSA-182198 title: Internalization of the CD8:Nef:AP-2 Complex:v-ATPase Complex findings: [] - id: Reactome:R-HSA-5252133 title: ATP6AP1 binds V-ATPase findings: [] - id: Reactome:R-HSA-74723 title: Endosome acidification findings: [] - id: Reactome:R-HSA-917841 title: Acidification of Tf:TfR1 containing endosome findings: [] - id: Reactome:R-HSA-9636397 title: PtpA binds ATP6V1H findings: [] - id: Reactome:R-HSA-9639286 title: RRAGC,D exchanges GTP for GDP findings: [] - id: Reactome:R-HSA-9640167 title: RRAGA,B exchanges GDP for GTP findings: [] - id: Reactome:R-HSA-9640168 title: >- v-ATPase:Ragulator:RRAGA,B:GTP:RRAGC,D:GDP:SLC38A9:Arginine dissociates yielding v-ATPase:Ragulator:RRAGA,B:GTP:RRAGC,D:GDP and SLC38A9:Arginine findings: [] - id: Reactome:R-HSA-9640175 title: v-ATPase:Ragulator:RagA,B:GDP:RagC,D:GDP binds SLC38A9:Arginine findings: [] - id: Reactome:R-HSA-9640195 title: RRAGA,B hydrolyzes GTP findings: [] - id: Reactome:R-HSA-9645598 title: RRAGC,D hydrolyzes GTP findings: [] - id: Reactome:R-HSA-9645608 title: v-ATPase:Ragulator:RRAGA,B:GTP:RRAGC,D:GDP binds mTORC1 findings: [] - id: Reactome:R-HSA-9646468 title: mTORC1 binds RHEB:GTP findings: [] - id: Reactome:R-HSA-9858916 title: MITF-M-dependent ATP6V1H gene expression findings: [] core_functions: - description: >- ATP6V1H is the regulatory H subunit of the V1 domain of the V-ATPase. It modulates ATPase coupling efficiency: in the free cytosolic V1 complex it inhibits futile ATP hydrolysis, and in the assembled holoenzyme it supports proton-coupled ATP hydrolysis. The H subunit contributes to the rotational mechanism of the V-ATPase by stabilizing the stator in V1, and is essential for regulated disassembly/reassembly of the complex in response to nutrient availability. contributes_to_molecular_function: id: GO:0046961 label: proton-transporting ATPase activity, rotational mechanism molecular_function: id: GO:0030234 label: enzyme regulator activity directly_involved_in: - id: GO:0007042 label: lysosomal lumen acidification - id: GO:0048388 label: endosomal lumen acidification locations: - id: GO:0005765 label: lysosomal membrane - id: GO:0005829 label: cytosol supported_by: - reference_id: file:human/ATP6V1H/ATP6V1H-uniprot.txt supporting_text: "The V1 complex consists of three catalytic AB heterodimers that form a heterohexamer, three peripheral stalks each consisting of EG heterodimers, one central rotor including subunits D and F, and the regulatory subunits C and H" - reference_id: PMID:9442887 supporting_text: The peripheral V1 domain, a 500-kDa complex responsible for ATP hydrolysis, contains at least eight different subunits of molecular weight 70-13 (subunits A-H) - description: >- ATP6V1H (subunit H) directly binds AP2M1 (the mu2 medium chain of AP-2) via armadillo repeat domains spanning residues 133-363, physically connecting the V-ATPase to the clathrin-mediated endocytic machinery. This is an independent function from the proton pump role and is responsible for the involvement of the V-ATPase in clathrin-coated vesicle formation and receptor internalization. HIV-1 and SIV Nef co-opt this interaction to force CD4/CD8 internalization. molecular_function: id: GO:0035615 label: clathrin-cargo adaptor activity directly_involved_in: - id: GO:0006897 label: endocytosis locations: - id: GO:0030665 label: clathrin-coated vesicle membrane supported_by: - reference_id: PMID:12032142 supporting_text: V1H binds to the C-terminal flexible loop in Nef from HIV-1 and to the medium chain (mu2) of the adaptor protein complex 2 (AP-2) in vitro and in vivo. The interaction sites of V1H and mu2 were mapped to a central region in V1H from positions 133 to 363, which contains 4 armadillo repeats suggested_questions: - question: Does the AP2M1-binding function of subunit H reflect a conserved role of V-ATPase in clathrin-coated vesicle biogenesis, or is the H subunit unusually specialized for this endocytic adaptor role compared to other V1 subunits? experts: - Geyer M - Peterlin BM - question: How does the regulatory switch of subunit H work mechanistically — what structural changes occur in H between the free V1 state (ATP hydrolysis inhibited) and the assembled holoenzyme state (ATP hydrolysis activated)? experts: - Forgac M - Rubinstein JL suggested_experiments: - hypothesis: The AP2M1-binding function of subunit H is required for normal clathrin-mediated endocytosis independent of V-ATPase proton pumping. description: >- Generate separation-of-function mutations in ATP6V1H that disrupt AP2M1 binding (within residues 133-363) without affecting V1 complex assembly or proton pump activity. Assess clathrin-mediated endocytosis of physiological cargo (transferrin receptor, EGF receptor) in cells expressing mutant versus wild-type H subunit. experiment_type: structure-function mutagenesis and receptor internalization assay - hypothesis: Regulated V1/V0 disassembly differentially affects the H subunit regulatory function. description: >- Quantify the ratio of V1H in membrane-bound (V-ATPase assembled) versus cytosolic (free V1) fractions under nutrient replete and starved conditions by subcellular fractionation and quantitative proteomics, and measure V1-ATPase activity in each fraction to directly test the inhibitory role of H in the free state. experiment_type: subcellular fractionation and ATPase activity assay