ATP5IF1 (also known as IF1 or ATPIF1) encodes the mitochondrial ATPase inhibitor, a small nuclear-encoded protein that reversibly inhibits the F1Fo-ATP synthase (complex V) to prevent wasteful ATP hydrolysis when the mitochondrial membrane potential collapses (e.g., during ischemia or hypoxia). IF1 is active as an antiparallel dimer at acidic pH (<6.7) and inactive as a tetramer at neutral pH. The N-terminal inhibitory region (residues 26-52) binds the alpha/beta catalytic interface of the F1 domain and contacts the gamma subunit to block rotary catalysis. IF1 also binds the OSCP subunit, which protects cancer cells from permeability transition pore-dependent apoptosis. Phosphorylation at Ser39 by a mitochondrial PKA-like activity inactivates IF1. The protein is overexpressed in many cancers and contributes to the glycolytic Warburg phenotype. IF1 also indirectly regulates heme synthesis in erythroid tissues and promotes ATP synthase dimerization, which influences cristae morphology.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | REMOVE | Summary: IBA annotation for cytoplasm based on phylogenetic inference. While IF1 is primarily a mitochondrial matrix protein, the precursor form is synthesized in the cytoplasm before import. The IBA also includes plant orthologs (TAIR locus) and bovine P01096, suggesting broad conservation. However, cytoplasm is a very general CC term and the primary active localization of IF1 is mitochondrial. Reason: The GOA qualifier is is_active_in, and the available evidence supports cytosolic synthesis/import transit rather than ATP5IF1 being active in cytoplasm. The functional location of IF1 is mitochondrial, especially the matrix-facing F1Fo-ATP synthase context. Supporting Evidence: PMID:10664857 cDNA coding the human homolog of the inhibitor protein was isolated and sequenced |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for mitochondrion based on phylogenetic inference across the ATPase inhibitor family. This is the primary active localization of IF1. Reason: Mitochondrial localization is the core cellular compartment for IF1. The mature protein functions in the mitochondrial matrix where it binds the F1 catalytic domain of ATP synthase. This is supported by multiple experimental studies (PMID:12110673, PMID:35926043) and UniProt annotation. Supporting Evidence: PMID:12110673 IF(1) could be co-isolated with F(1)F(0) when the immunocapture procedure was carried out at pH 6.5 but was absent when the ATP synthase was isolated at pH 8.0 |
| GO:0006783 heme biosynthetic process | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA annotation for heme biosynthetic process based on phylogenetic inference from mouse (MGI:1196457) and zebrafish (ZFIN:ZDB-GENE-070410-36) orthologs. Shah et al. (2012, PMID:23135403) demonstrated that Atpif1 regulates heme synthesis in developing erythroblasts by modulating mitochondrial pH and redox potential, allowing FECH to catalyze iron incorporation into protoporphyrin IX. Reason: This is a genuine but indirect role of IF1. The protein does not directly participate in heme biosynthetic enzymology; rather, by inhibiting ATP hydrolysis, IF1 maintains mitochondrial pH and redox conditions favorable for FECH activity. UniProt explicitly states: "Indirectly acts as a regulator of heme synthesis in erythroid tissues: regulates heme synthesis by modulating the mitochondrial pH and redox potential, allowing FECH to efficiently catalyze the incorporation of iron into protoporphyrin IX to produce heme" (PMID:23135403). This is a secondary consequence of its primary ATPase inhibitor activity, relevant mainly in erythroid tissues. Supporting Evidence: PMID:23135403 Mitochondrial Atpif1 regulates haem synthesis in developing erythroblasts |
| GO:0030218 erythrocyte differentiation | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA annotation for erythrocyte differentiation based on phylogenetic inference from mouse and zebrafish orthologs. The evidence comes from PMID:23135403 showing that Atpif1 is required for proper heme synthesis during erythroid development. Reason: Like heme biosynthesis, erythrocyte differentiation is an indirect downstream consequence of IF1's ATPase inhibitor activity. IF1 is not an erythroid-specific transcription factor or signaling molecule; it supports erythropoiesis by maintaining mitochondrial conditions needed for heme synthesis. This represents a tissue-specific pleiotropic effect rather than a core molecular function. Supporting Evidence: PMID:23135403 Mitochondrial Atpif1 regulates haem synthesis in developing erythroblasts |
| GO:0042030 ATPase inhibitor activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for ATPase inhibitor activity based on phylogenetic inference across the ATPase inhibitor family (bovine P01096, rat RGD:2181, and human Q9UII2). This is the defining molecular function of IF1. Reason: ATPase inhibitor activity is the core molecular function of ATP5IF1. The protein is named for this activity and belongs to the ATPase inhibitor family. IF1 inhibits the ATP hydrolase activity of F1Fo-ATP synthase, preventing wasteful ATP consumption when the proton gradient collapses (PMID:12110673, PMID:15528193, PMID:24005319). The IBA correctly reflects the conserved function across mammals. Supporting Evidence: PMID:12110673 The captured complex V displayed ATP hydrolysis activity that was fully oligomycin and inhibitor protein IF(1)-sensitive PMID:15528193 IF1 protein bound to purified F(1) ATP synthase and inhibited F(1)-dependent ATP hydrolysis consistent with its reported activity in studies of mitochondria file:human/ATP5IF1/ATP5IF1-deep-research-falcon.md IF1 is a reversible, pH-sensitive inhibitor that primarily prevents wasteful ATP hydrolysis when ΞΟm collapses, but can also inhibit ATP synthesis in some contexts |
| GO:0051117 ATPase binding | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for ATPase binding based on phylogenetic inference. IF1 physically binds the F1 catalytic domain of ATP synthase, contacting the alpha/beta subunit interface and the gamma subunit. Reason: ATPase binding is a core function that underlies the inhibitory activity of IF1. Structural and biochemical studies demonstrate direct binding to the F1 domain. The IBA annotation is consistent with the well-established mechanism of IF1 action. Aggeler et al. (PMID:12110673) showed IF1 co-isolates with F1Fo at pH 6.5, and UniProt documents the binding interface at the alpha-beta subunit interface (residues 26-52). Supporting Evidence: PMID:12110673 IF(1) could be co-isolated with F(1)F(0) when the immunocapture procedure was carried out at pH 6.5 |
| GO:0005739 mitochondrion | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation for mitochondrion based on combined automated methods including InterPro domain (IPR007648) and UniProt subcellular location annotation. Consistent with all other evidence for mitochondrial localization. Reason: This electronic annotation is consistent with the well-established mitochondrial localization of IF1, supported by multiple experimental evidence codes (IDA, HTP, HDA, ISS, TAS, IBA). The InterPro domain IPR007648 (ATPase_inhibitor_mt) is specifically a mitochondrial domain. |
| GO:0042030 ATPase inhibitor activity | IEA GO_REF:0000002 | ACCEPT | Summary: IEA annotation for ATPase inhibitor activity based on InterPro domain IPR007648 mapping. This is the defining function of the protein family. Reason: The InterPro-based electronic annotation correctly identifies the core molecular function. The ATPase_inhibitor_mt domain (IPR007648) is directly associated with ATPase inhibitor activity, and this is the primary function of IF1 supported by extensive experimental evidence. |
| GO:0005515 protein binding | IPI PMID:28514442 Architecture of the human interactome defines protein commun... | MODIFY | Summary: IPI annotation for protein binding from the BioPlex 2.0 human interactome study (Huttlin et al. 2017). The WITH column indicates binding to P06576 (ATP5F1B, the beta subunit of F1-ATP synthase). This interaction is biologically meaningful and well-established. Reason: While the interaction with ATP5F1B (beta subunit) is real and reflects the core mechanism of IF1, "protein binding" (GO:0005515) is uninformative. The specific interaction with the beta subunit of ATP synthase is the mechanistic basis of IF1's inhibitory function. A more specific term should be used. Proposed replacements: mitochondrial proton-transporting ATP synthase complex binding Supporting Evidence: PMID:28514442 Architecture of the human interactome defines protein communities and disease networks |
| GO:0005515 protein binding | IPI PMID:30021884 Histone Interaction Landscapes Visualized by Crosslinking Ma... | REMOVE | Summary: IPI annotation for protein binding from a crosslinking mass spectrometry study of intact cell nuclei (Fasci et al. 2018). The WITH column indicates binding to P06576 (ATP5F1B). This study focused on histone interactions in nuclei, making ATP5IF1 detection likely a contaminant or crossreactive hit. Reason: This intact-nuclei XL-MS study does not provide reliable support for a physiological mitochondrial ATP5IF1-ATP5F1B interaction. The core ATP synthase complex binding function is already supported by direct mitochondrial evidence from other publications, so this nuclear-context protein-binding row should not be modified into that term. Supporting Evidence: PMID:30021884 Histone Interaction Landscapes Visualized by Crosslinking Mass Spectrometry in Intact Cell Nuclei |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | MARK AS OVER ANNOTATED | Summary: IPI annotation for protein binding from the HuRI reference binary interactome map (Luck et al. 2020). The WITH column indicates binding to Q9HAQ2 (KIF9) and Q9NRD5 (PICK1). These are high-throughput Y2H hits with no clear biological relevance to IF1's known function. Reason: KIF9 and PICK1 are not known to have any functional relationship with mitochondrial ATP synthase or IF1's inhibitory activity. These likely represent false-positive or non-physiological interactions from high-throughput Y2H screening. The generic "protein binding" term combined with HTP interactome partners of unclear relevance makes this an over-annotation. Supporting Evidence: PMID:32296183 A reference map of the human binary protein interactome |
| GO:0005515 protein binding | IPI PMID:32807793 OSMR controls glioma stem cell respiration and confers resis... | MARK AS OVER ANNOTATED | Summary: IPI annotation for protein binding from Sharanek et al. 2020, studying mitochondrial OSMR in glioblastoma. The WITH column indicates binding to Q99650 (OSMR). The paper found OSMR localizes to mitochondria and interacts with complex I, and IF1 was detected as an interactor. Reason: While OSMR was shown to localize to mitochondria, the interaction with IF1 is likely an indirect association within the mitochondrial inner membrane protein network rather than a direct functional interaction. The paper focuses on OSMR-complex I interactions, not IF1. The generic "protein binding" term does not capture any meaningful functional relationship. Supporting Evidence: PMID:32807793 OSMR controls glioma stem cell respiration and confers resistance of glioblastoma to ionizing radiation |
| GO:0005515 protein binding | IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ... | MARK AS OVER ANNOTATED | Summary: IPI annotation for protein binding from a neurodegenerative disease interactome mapping study (Haenig et al. 2020). The WITH column lists many diverse proteins (PMP22, DMWD, NEFL, TOR1A, KLF11, DNAJB6, DNM2, FGFR3, GLE1, GRN, GSN, HRAS, A2M, ADRB2, MECP2, NUP58, SPRED1, P28329-3/CHAT, P28799-2/GRN). These represent high-throughput Y2H hits from a disease-focused interactome screen. Reason: This is a large-scale interactome study focused on neurodegenerative disease proteins. The vast majority of these interactors (NEFL, MECP2, HRAS, FGFR3, GSN, A2M, etc.) have no plausible direct functional relationship with mitochondrial IF1. These are likely false positives or non-physiological interactions from Y2H. The sheer number and diversity of partners argues against specificity. "Protein binding" is already uninformative and these interactions do not add functional insight. Supporting Evidence: PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins and Uncovers Widespread Protein Aggregation in Affected Brains |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | MODIFY | Summary: IPI annotation for protein binding from BioPlex 3.0 (Huttlin et al. 2021). The WITH column indicates binding to P06576 (ATP5F1B, beta subunit of F1-ATP synthase). This is the same core interaction as PMID:28514442. Reason: The interaction with ATP5F1B is the core functional binding partner of IF1 and is well-established. However, "protein binding" is uninformative. A more specific term should be used. Proposed replacements: mitochondrial proton-transporting ATP synthase complex binding Supporting Evidence: PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome |
| GO:0005515 protein binding | IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func... | MODIFY | Summary: IPI annotation for protein binding from Schaffer et al. 2025 multimodal cell maps study. The WITH column indicates binding to P06576 (ATP5F1B). Again, the same core interaction with the beta subunit. Reason: Same rationale as for PMID:28514442 and PMID:33961781. The interaction with ATP5F1B is real but "protein binding" is uninformative. A more specific MF term exists. Proposed replacements: mitochondrial proton-transporting ATP synthase complex binding Supporting Evidence: PMID:40205054 Multimodal cell maps as a foundation for structural and functional genomics |
| GO:0006783 heme biosynthetic process | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: IEA annotation for heme biosynthetic process transferred from mouse ortholog O35143 via Ensembl Compara. Consistent with the IBA annotation and the experimental evidence from Shah et al. (PMID:23135403). Reason: This electronic transfer from the mouse ortholog is consistent with the IBA annotation and PMID:23135403 showing IF1 regulates heme synthesis indirectly. Same rationale as the IBA annotation: this is a genuine but non-core function. |
| GO:0030218 erythrocyte differentiation | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: IEA annotation for erythrocyte differentiation transferred from mouse ortholog O35143 via Ensembl Compara. Consistent with the IBA annotation and PMID:23135403. Reason: Same rationale as the IBA annotation for this term: erythrocyte differentiation is a tissue-specific downstream consequence of IF1's ATPase inhibitor activity supporting heme synthesis. |
| GO:0045732 positive regulation of protein catabolic process | IMP PMID:24005319 Genome-wide RNAi screen identifies ATPase inhibitory factor ... | KEEP AS NON CORE | Summary: IMP annotation from Lefebvre et al. 2013 genome-wide RNAi screen that identified ATPIF1 as essential for PARK2 recruitment and mitophagy. ATPIF1 knockdown blocked PARK2-dependent ubiquitination and subsequent mitophagy of damaged mitochondria, which involves protein catabolism of ubiquitinated mitochondrial substrates. Reason: The connection to protein catabolism is through the PINK1-PARK2 mitophagy pathway. ATPIF1 promotes mitochondrial depolarization during uncoupling, which triggers PARK2 recruitment and ubiquitination of mitochondrial proteins for proteasomal/autophagic degradation. This is an indirect downstream consequence of IF1's primary ATPase inhibitor activity. While experimentally demonstrated, it is not a core function. Supporting Evidence: PMID:24005319 we identified ATPase inhibitory factor 1 (ATPIF1/IF1) as essential for PARK2 recruitment and mitophagy in cultured cells |
| GO:1905707 negative regulation of mitochondrial ATP synthesis coupled proton transport | IMP PMID:24005319 Genome-wide RNAi screen identifies ATPase inhibitory factor ... | ACCEPT | Summary: IMP annotation from Lefebvre et al. 2013 showing that ATPIF1 blocks ATP synthase from running in reverse (as an ATPase) during uncoupling. The annotation captures the process-level consequence of IF1's ATPase inhibitor activity on ATP synthesis coupled proton transport. Reason: This annotation correctly captures the core biological process function of IF1. During mitochondrial uncoupling, the F1Fo-ATP synthase can reverse to hydrolyze ATP and pump protons. IF1 inhibits this reversal, effectively negatively regulating the overall ATP synthesis coupled proton transport process. Lefebvre et al. showed "ATPIF1 promotes collapse of delta-psi and activation of the PINK-PARK2 mitophagy pathway by blocking the ATPase activity of the F1-Fo ATP synthase" (PMID:24005319). Supporting Evidence: PMID:24005319 During uncoupling, ATPIF1 promotes collapse of ΞΞ¨ and activation of the PINK-PARK2 mitophagy pathway by blocking the ATPase activity of the F 1-Fo ATP synthase |
| GO:0005739 mitochondrion | IDA GO_REF:0000052 | ACCEPT | Summary: IDA annotation for mitochondrion based on curation of immunofluorescence data (Human Protein Atlas). Direct visualization of IF1 in mitochondria. Reason: Direct immunofluorescence evidence for mitochondrial localization is consistent with all other evidence. HPA data provides independent confirmation of the core localization. |
| GO:0002931 response to ischemia | IDA PMID:35926043 Mitochondrial remodeling and ischemic protection by G protei... | KEEP AS NON CORE | Summary: IDA annotation from Wyant et al. 2022 (Science) showing that ATPIF1 is involved in ischemic protection. GPR35 activation led to ATPIF1-dependent ATP synthase dimerization that prevented ATP loss during ischemia. The study demonstrated that "Activated GPR35, in an ATPIF1-dependent and pertussis toxin-sensitive manner, induced ATP synthase dimerization, which prevented ATP loss upon ischemia." Reason: Response to ischemia is biologically important and experimentally demonstrated, but it represents a physiological context in which IF1's primary ATPase inhibitor function is deployed, rather than the core function itself. IF1's role in ischemic protection is a consequence of its ability to prevent ATP hydrolysis when the proton gradient collapses. This is a key physiological role but secondary to the molecular function. Supporting Evidence: PMID:35926043 Activated GPR35, in an ATPIF1-dependent and pertussis toxin-sensitive manner, induced ATP synthase dimerization, which prevented ATP loss upon ischemia |
| GO:0010667 negative regulation of cardiac muscle cell apoptotic process | IDA PMID:35926043 Mitochondrial remodeling and ischemic protection by G protei... | UNDECIDED | Summary: IDA annotation from Wyant et al. 2022 showing that ATPIF1-dependent ATP synthase dimerization contributes to cardiac protection during ischemia. By preventing ATP depletion, IF1 protects cardiac cells from apoptosis during ischemic stress. Reason: The accessible evidence supports GPR35/ATPIF1-dependent ATP synthase dimerization and ATP preservation during ischemia, but the cached support does not directly establish negative regulation of cardiac muscle cell apoptosis. Treat this as undecided until direct apoptosis evidence from the paper is available. Supporting Evidence: PMID:35926043 Activated GPR35, in an ATPIF1-dependent and pertussis toxin-sensitive manner, induced ATP synthase dimerization, which prevented ATP loss upon ischemia |
| GO:0042030 ATPase inhibitor activity | TAS PMID:24005319 Genome-wide RNAi screen identifies ATPase inhibitory factor ... | ACCEPT | Summary: TAS annotation for ATPase inhibitor activity based on Lefebvre et al. 2013. The paper describes ATPIF1 as "blocking the ATPase activity of the F1-Fo ATP synthase" during uncoupling. Reason: ATPase inhibitor activity is the core molecular function. This TAS annotation is consistent with all other evidence for this function. The paper explicitly describes ATPIF1 blocking ATPase activity. Supporting Evidence: PMID:24005319 During uncoupling, ATPIF1 promotes collapse of ΞΞ¨ and activation of the PINK-PARK2 mitophagy pathway by blocking the ATPase activity of the F 1-Fo ATP synthase |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | ACCEPT | Summary: HTP annotation for mitochondrion from Morgenstern et al. 2021, a quantitative high-confidence human mitochondrial proteome study. ATP5IF1 was identified as a high-confidence mitochondrial protein. Reason: This high-throughput proteomics study provides quantitative evidence for mitochondrial localization. Consistent with all other evidence codes for this localization. Supporting Evidence: PMID:34800366 Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context |
| GO:1905707 negative regulation of mitochondrial ATP synthesis coupled proton transport | ISS GO_REF:0000024 | ACCEPT | Summary: ISS annotation transferred from bovine ortholog P01096. The bovine IF1 was the first characterized member of this family and shares high sequence conservation with human IF1. The function is well-conserved. Reason: This ISS annotation is consistent with the IMP annotation from PMID:24005319 for the same GO term. The bovine ortholog is the best-studied member of this family, and the transfer is appropriate given high sequence conservation and shared function. |
| GO:0032991 protein-containing complex | ISS GO_REF:0000024 | REMOVE | Summary: ISS annotation indicating IF1 is part of a protein-containing complex, transferred from bovine ortholog P01096. IF1 forms homodimers and associates with the F1Fo-ATP synthase complex. Reason: While IF1 is indeed part of protein complexes (homodimers and the IF1-ATP synthase complex), "protein-containing complex" is too generic and there is no appropriate same-aspect CC replacement here. The relevant biology is already captured by more specific annotations: mitochondrial localization and the supported MF annotation for mitochondrial proton-transporting ATP synthase complex binding (GO:0140260). |
| GO:0042802 identical protein binding | ISS GO_REF:0000024 | ACCEPT | Summary: ISS annotation for identical protein binding (homodimerization) transferred from bovine ortholog P01096. IF1 forms antiparallel dimers at acidic pH, which is the active inhibitory form, and homotetramers at neutral pH, which is the inactive form. Reason: Homodimerization is a critical regulatory mechanism for IF1. UniProt states: "Homodimer; represents the active form and is present at a pH value below 6.5. Homotetramer; represents the inactive form and is present at a pH value above 7.0." The antiparallel coiled-coil dimer (residues 74-106) is essential for the inhibitory mechanism. While "identical protein binding" is somewhat generic, it accurately captures the homodimerization property. Supporting Evidence: PMID:12110673 IF(1) could be co-isolated with F(1)F(0) when the immunocapture procedure was carried out at pH 6.5 but was absent when the ATP synthase was isolated at pH 8.0 |
| GO:0140260 mitochondrial proton-transporting ATP synthase complex binding | IDA PMID:12110673 A functionally active human F1F0 ATPase can be purified by i... | ACCEPT | Summary: IDA annotation for direct binding to the mitochondrial ATP synthase complex, from Aggeler et al. 2002. The study demonstrated co-immunoprecipitation of IF1 with F1Fo-ATP synthase from human heart mitochondria in a pH-dependent manner. Reason: This is a core molecular function annotation. Aggeler et al. directly demonstrated that IF1 co-purifies with immunocaptured F1Fo-ATP synthase at pH 6.5 but not at pH 8.0, confirming direct pH-dependent binding. The captured complex could be inhibited >90% by recombinant IF1 and activated >10-fold by pH 8.0 release. Supporting Evidence: PMID:12110673 IF(1) could be co-isolated with F(1)F(0) when the immunocapture procedure was carried out at pH 6.5 but was absent when the ATP synthase was isolated at pH 8.0 PMID:12110673 Immunocaptured F(1)F(0) lacking IF(1) could be inhibited by more than 90% by addition of recombinant inhibitor protein |
| GO:1905091 positive regulation of type 2 mitophagy | IMP PMID:24005319 Genome-wide RNAi screen identifies ATPase inhibitory factor ... | KEEP AS NON CORE | Summary: IMP annotation from Lefebvre et al. 2013 genome-wide RNAi screen. ATPIF1 was identified as essential for PARK2 recruitment to depolarized mitochondria and subsequent mitophagy. ATPIF1 promotes mitochondrial depolarization by blocking reverse ATP synthase activity, which is required for PINK1 stabilization and PARK2 recruitment. Reason: Mitophagy regulation is an experimentally supported but indirect consequence of IF1's primary ATPase inhibitor activity. IF1 promotes mitophagy by ensuring complete mitochondrial depolarization during uncoupling (by preventing ATP hydrolysis-driven proton pumping), which allows PINK1 accumulation and PARK2 recruitment. This is a downstream biological process rather than a core function. Supporting Evidence: PMID:24005319 we identified ATPase inhibitory factor 1 (ATPIF1/IF1) as essential for PARK2 recruitment and mitophagy in cultured cells PMID:24005319 Restoration of ATPIF1 in Rho0 cells, which lack mtDNA and a functional electron transport chain, lowers ΞΞ¨ and triggers PARK2 recruitment |
| GO:0019899 enzyme binding | IPI PMID:21106936 Regenerative protein thymosin beta-4 is a novel regulator of... | MODIFY | Summary: IPI annotation for enzyme binding from Freeman et al. 2011. The study focused on thymosin beta-4 (Tbeta4) as a regulator of cell surface ATP synthase in endothelial cells. IF1 was described as having structural similarity to Tbeta4 in silico. The WITH column indicates P06576 (ATP5F1B) and P25705 (ATP5F1A), the beta and alpha subunits of F1-ATP synthase. Reason: The binding partners (ATP5F1A and ATP5F1B, the alpha and beta subunits of F1-ATP synthase) are correct and represent the core binding target of IF1. However, "enzyme binding" is too generic. The specific binding to the ATP synthase complex is well-characterized and a more specific term exists. Proposed replacements: mitochondrial proton-transporting ATP synthase complex binding Supporting Evidence: PMID:21106936 we identified common amphiphilic alpha-helical structural similarities between beta-thymosins and the inhibitory factor 1 (IF1), an inhibitor of ATP synthase hydrolysis |
| GO:1903747 regulation of protein localization to mitochondrion | IMP PMID:24005319 Genome-wide RNAi screen identifies ATPase inhibitory factor ... | KEEP AS NON CORE | Summary: IMP annotation from Lefebvre et al. 2013. ATPIF1 knockdown prevented PARK2 translocation to mitochondria. By promoting mitochondrial depolarization (blocking reverse ATP synthase), ATPIF1 enables the PINK1-dependent recruitment of PARK2 to damaged mitochondria. Reason: This annotation captures a specific aspect of the mitophagy pathway: IF1-dependent regulation of PARK2 localization to mitochondria. While experimentally supported by the RNAi screen, this is an indirect downstream effect. IF1 does not directly regulate protein localization machinery; it enables PARK2 recruitment by ensuring mitochondrial depolarization through its ATPase inhibitor activity. Supporting Evidence: PMID:24005319 we identified ATPase inhibitory factor 1 (ATPIF1/IF1) as essential for PARK2 recruitment and mitophagy in cultured cells |
| GO:0051882 mitochondrial depolarization | IMP PMID:24005319 Genome-wide RNAi screen identifies ATPase inhibitory factor ... | ACCEPT | Summary: IMP annotation from Lefebvre et al. 2013. ATPIF1 promotes collapse of the mitochondrial membrane potential during uncoupling by blocking the reverse ATPase activity that would otherwise maintain membrane potential by pumping protons. Reason: Mitochondrial depolarization is a direct and proximal consequence of IF1's core ATPase inhibitor activity. When the electron transport chain fails or is uncoupled, ATP synthase reverses to hydrolyze ATP and pump protons, partially maintaining membrane potential. IF1 blocks this reversal, allowing complete depolarization. This is a direct functional outcome and closely tied to the core mechanism. The paper states: "During uncoupling, ATPIF1 promotes collapse of delta-psi... by blocking the ATPase activity of the F1-Fo ATP synthase." Supporting Evidence: PMID:24005319 During uncoupling, ATPIF1 promotes collapse of ΞΞ¨ and activation of the PINK-PARK2 mitophagy pathway by blocking the ATPase activity of the F 1-Fo ATP synthase PMID:24005319 Restoration of ATPIF1 in Rho0 cells, which lack mtDNA and a functional electron transport chain, lowers ΞΞ¨ and triggers PARK2 recruitment |
| GO:0005739 mitochondrion | HDA PMID:20833797 Phosphoproteome analysis of functional mitochondria isolated... | ACCEPT | Summary: HDA annotation for mitochondrial localization from Zhao et al. 2011, a phosphoproteomics study of functional mitochondria isolated from human muscle. IF1 was detected in the mitochondrial phosphoproteome. Reason: This high-throughput direct assay evidence for mitochondrial localization is consistent with all other evidence. The protein was identified in isolated mitochondria from human skeletal muscle. Supporting Evidence: PMID:20833797 Phosphoproteome analysis of functional mitochondria isolated from resting human muscle reveals extensive phosphorylation of inner membrane protein complexes and enzymes |
| GO:0042030 ATPase inhibitor activity | ISS GO_REF:0000024 | ACCEPT | Summary: ISS annotation for ATPase inhibitor activity transferred from bovine ortholog P01096. The bovine IF1 is the best-characterized member of this protein family. Reason: This is the core molecular function, and the transfer from the bovine ortholog is appropriate given high sequence conservation and identical function. Consistent with IDA and IBA annotations for the same term. |
| GO:0005739 mitochondrion | IDA PMID:12110673 A functionally active human F1F0 ATPase can be purified by i... | ACCEPT | Summary: IDA annotation for mitochondrial localization from Aggeler et al. 2002. IF1 was identified as a subunit of the immunocaptured F1Fo-ATP synthase complex from human heart mitochondria and fibroblasts. Reason: Direct experimental evidence from immunocapture of mitochondrial ATP synthase complex. IF1 was detected with specific antibody and co-purified with the complex from mitochondria. Supporting Evidence: PMID:12110673 The immunoprecipitated F(1)F(0) contained a full complement of subunits that were identified with specific antibodies against five of the subunits (alpha, beta, OSCP, d, and IF(1)) |
| GO:0042030 ATPase inhibitor activity | IDA PMID:12110673 A functionally active human F1F0 ATPase can be purified by i... | ACCEPT | Summary: IDA annotation for ATPase inhibitor activity from Aggeler et al. 2002. The study directly demonstrated that recombinant IF1 inhibited ATP hydrolysis by immunocaptured F1Fo-ATP synthase by >90%, and that removal of IF1 at pH 8.0 activated the enzyme >10-fold. Reason: This is direct experimental evidence for the core molecular function. The quantitative inhibition data (>90% inhibition by recombinant IF1, >10-fold activation upon IF1 release) provides strong support for ATPase inhibitor activity. Supporting Evidence: PMID:12110673 Immunocaptured F(1)F(0) lacking IF(1) could be inhibited by more than 90% by addition of recombinant inhibitor protein, and conversely, F(1)F(0) containing IF(1) could be activated more than 10-fold by brief exposure to pH 8.0, inducing the release of inhibitor protein |
| GO:0001525 angiogenesis | TAS PMID:15528193 An Inhibitor of the F1 subunit of ATP synthase (IF1) modulat... | KEEP AS NON CORE | Summary: TAS annotation for angiogenesis from Burwick et al. 2005. The study explored IF1's effect on cell surface ATP synthase in endothelial cells and its relationship with angiostatin-mediated anti-angiogenesis. IF1 was proposed to have a "protective role for EC in the tumor microenvironment" that could be overridden by angiostatin. Reason: The paper studied IF1 in the context of cell surface ATP synthase and angiostatin, concluding that IF1 is NOT an angiostatin mimetic and only "slightly inhibited cell proliferation compared with angiostatin." The connection to angiogenesis is indirect through the cell surface ATP synthase-angiostatin axis. This is a peripheral, non-core function related to the unusual cell surface localization of IF1/ATP synthase, not the primary mitochondrial function. Supporting Evidence: PMID:15528193 We propose that IF1 is not an angiostatin mimetic, but it can serve a protective role for EC in the tumor microenvironment PMID:15528193 IF1 did not inhibit EC differentiation to form tubes and only slightly inhibited cell proliferation compared with angiostatin |
| GO:0001937 negative regulation of endothelial cell proliferation | IDA PMID:15528193 An Inhibitor of the F1 subunit of ATP synthase (IF1) modulat... | MARK AS OVER ANNOTATED | Summary: IDA annotation from Burwick et al. 2005 showing that exogenous IF1 "only slightly inhibited cell proliferation compared with angiostatin." The paper explicitly states the effect was minor. Reason: The paper itself states IF1 "only slightly inhibited cell proliferation compared with angiostatin." This is a marginal effect observed with exogenous IF1 on cell surface ATP synthase, not the protein's primary function. The anti-proliferative effect was weak and the authors concluded IF1 is "not an angiostatin mimetic." This represents an over-annotation of a minor experimental observation. Supporting Evidence: PMID:15528193 IF1 did not inhibit EC differentiation to form tubes and only slightly inhibited cell proliferation compared with angiostatin |
| GO:0005516 calmodulin binding | ISS GO_REF:0000024 | UNDECIDED | Summary: ISS annotation for calmodulin binding transferred from bovine ortholog P01096. Calmodulin has been reported to interact with IF1 in bovine systems, potentially regulating its activity or oligomeric state. Reason: The calmodulin binding annotation is transferred from the bovine ortholog. While there is some evidence for calmodulin-IF1 interaction in bovine systems, the physiological significance and whether this applies to human IF1 is not well-established in the publications available for review. The core regulatory mechanisms of IF1 (pH-dependent oligomerization and Ser39 phosphorylation) are well-documented, but calmodulin regulation is less certain. Without access to the primary bovine literature supporting this claim, this should remain undecided. |
| GO:0005739 mitochondrion | ISS GO_REF:0000024 | ACCEPT | Summary: ISS annotation for mitochondrion transferred from bovine ortholog P01096. Consistent with all other evidence for mitochondrial localization. Reason: Mitochondrial localization is well-established for IF1 across species. This ISS transfer is consistent with IDA, IBA, IEA, HTP, HDA, and TAS evidence for the same localization. |
| GO:0009986 cell surface | IDA PMID:15528193 An Inhibitor of the F1 subunit of ATP synthase (IF1) modulat... | KEEP AS NON CORE | Summary: IDA annotation for cell surface localization from Burwick et al. 2005. The study showed IF1 interacting with cell surface F1-ATP synthase on endothelial cells. The paper demonstrated IF1 binding to purified F1 and its effects on cell surface ATP hydrolysis. Reason: Cell surface localization of IF1 (and ATP synthase) has been reported on endothelial cells. While the primary localization of IF1 is mitochondrial, the cell surface localization appears to be a genuine but secondary location. The biological significance of cell surface IF1 is debated, and it may represent ectopic localization in certain cell types rather than a core function. Supporting Evidence: PMID:15528193 IF1 protein bound to purified F(1) ATP synthase and inhibited F(1)-dependent ATP hydrolysis consistent with its reported activity in studies of mitochondria |
| GO:0042030 ATPase inhibitor activity | IDA PMID:15528193 An Inhibitor of the F1 subunit of ATP synthase (IF1) modulat... | ACCEPT | Summary: IDA annotation for ATPase inhibitor activity from Burwick et al. 2005. The study confirmed IF1 inhibited F1-dependent ATP hydrolysis both with purified enzyme and on the cell surface. Reason: The paper directly demonstrates ATPase inhibitor activity, consistent with the core function. IF1 inhibited ATP hydrolysis but notably "did not inhibit ATP synthesis" on the cell surface, confirming its specific ATPase (hydrolysis) inhibitor activity. Supporting Evidence: PMID:15528193 IF1 protein bound to purified F(1) ATP synthase and inhibited F(1)-dependent ATP hydrolysis consistent with its reported activity in studies of mitochondria PMID:15528193 IF1 inhibited ATP hydrolysis but not ATP synthesis, in contrast to angiostatin, which inhibited both |
| GO:0043532 angiostatin binding | IDA PMID:15528193 An Inhibitor of the F1 subunit of ATP synthase (IF1) modulat... | UNDECIDED | Summary: IDA annotation for angiostatin binding from Burwick et al. 2005. The study showed that "angiostatin blocks IF1 binding to ATP synthase and abolishes its ability to conserve ATP," suggesting overlapping binding sites. However, this demonstrates competition for ATP synthase binding, not necessarily direct IF1-angiostatin binding. Reason: The paper demonstrates that angiostatin and IF1 compete for binding to ATP synthase, which implies overlapping binding sites on the enzyme rather than direct IF1-angiostatin binding. The statement "there is a relationship between the binding sites of IF1 and angiostatin on ATP synthase" supports competition, not direct binding. Without access to the full text to determine whether direct binding was actually demonstrated (rather than competition), this remains unclear. Supporting Evidence: PMID:15528193 angiostatin blocks IF1 binding to ATP synthase and abolishes its ability to conserve ATP PMID:15528193 These data suggest that there is a relationship between the binding sites of IF1 and angiostatin on ATP synthase |
| GO:0051117 ATPase binding | ISS GO_REF:0000024 | ACCEPT | Summary: ISS annotation for ATPase binding transferred from bovine ortholog P01096. Consistent with the IBA and IDA annotations for this term. Reason: ATPase binding is a core function, and this ISS transfer from the bovine ortholog is well-supported by multiple experimental evidence types for the same term. |
| GO:0051117 ATPase binding | IDA PMID:15528193 An Inhibitor of the F1 subunit of ATP synthase (IF1) modulat... | ACCEPT | Summary: IDA annotation for ATPase binding from Burwick et al. 2005. The study demonstrated direct binding of IF1 to purified F1 ATP synthase. Reason: The paper directly demonstrates IF1 binding to F1-ATP synthase. This is a core function well-supported by multiple lines of evidence. Supporting Evidence: PMID:15528193 IF1 protein bound to purified F(1) ATP synthase and inhibited F(1)-dependent ATP hydrolysis |
| GO:0051346 negative regulation of hydrolase activity | IDA PMID:15528193 An Inhibitor of the F1 subunit of ATP synthase (IF1) modulat... | ACCEPT | Summary: IDA annotation for negative regulation of hydrolase activity from Burwick et al. 2005. IF1 inhibited ATP hydrolysis activity of the F1-ATP synthase both in purified form and on the cell surface. Reason: This annotation accurately captures the core process-level function of IF1 at a somewhat general level. IF1 negatively regulates the ATP hydrolase activity of F1Fo-ATP synthase. While GO:1905707 (negative regulation of mitochondrial ATP synthesis coupled proton transport) is more specific, this term is also accurate as a broader description of the mechanism. Supporting Evidence: PMID:15528193 IF1 inhibited ATP hydrolysis but not ATP synthesis |
| GO:0004857 enzyme inhibitor activity | TAS PMID:10664857 Nucleotide sequence of cDNA coding the mitochondrial precurs... | MODIFY | Summary: TAS annotation for enzyme inhibitor activity from Ichikawa et al. 1999, the paper reporting the human cDNA sequence. The paper describes the protein as "the ATPase inhibitor" based on sequence homology to the bovine inhibitor protein. Reason: While IF1 is indeed an enzyme inhibitor, "enzyme inhibitor activity" (GO:0004857) is too general. The more specific term "ATPase inhibitor activity" (GO:0042030) is already annotated and better captures the specific function. This general term should be replaced with the more specific one. Proposed replacements: ATPase inhibitor activity Supporting Evidence: PMID:10664857 cDNA coding the human homolog of the inhibitor protein was isolated and sequenced |
| GO:0005739 mitochondrion | TAS PMID:10664857 Nucleotide sequence of cDNA coding the mitochondrial precurs... | ACCEPT | Summary: TAS annotation for mitochondrion from Ichikawa et al. 1999. The paper describes the protein as "the mitochondrial precursor protein of the ATPase inhibitor from humans." Reason: Mitochondrial localization is stated in the paper title and is consistent with all other evidence. The paper describes the mitochondrial transit peptide and identifies the protein as a mitochondrial ATPase inhibitor. Supporting Evidence: PMID:10664857 cDNA coding the mitochondrial precursor protein of the ATPase inhibitor from humans |
| GO:0006091 generation of precursor metabolites and energy | TAS PMID:10664857 Nucleotide sequence of cDNA coding the mitochondrial precurs... | MODIFY | Summary: TAS annotation for generation of precursor metabolites and energy from Ichikawa et al. 1999. This is a very broad biological process term covering all of energy metabolism. Reason: This term is too broad. IF1 does not generally participate in "generation of precursor metabolites and energy" -- it specifically inhibits ATP hydrolysis by the F1Fo-ATP synthase. The more specific term GO:1905707 (negative regulation of mitochondrial ATP synthesis coupled proton transport) better captures the actual process. Alternatively, GO:1903578 (regulation of ATP metabolic process) would be more appropriate. Proposed replacements: negative regulation of mitochondrial ATP synthesis coupled proton transport |
| GO:0005759 mitochondrial matrix | IDA PMID:12110673 A functionally active human F1F0 ATPase can be purified by i... | NEW | Summary: The mature IF1 protein functions in the mitochondrial matrix, where it binds the F1 catalytic domain on the matrix-facing side of the inner membrane. While "mitochondrion" is annotated, the more specific sub-compartment (mitochondrial matrix) is not explicitly annotated. UniProt states: "Mitochondrion" as subcellular location, and the deep research notes that IF1 acts "on the matrix side of the F1 catalytic domain." Cryo-EM structures (PDB: 8H9E, 8H9L, 8H9S, 8H9U, 8KI3) place IF1 bound to the F1 domain which projects into the matrix. Reason: The mitochondrial matrix is the specific sub-compartment where IF1 is active. The F1 domain that IF1 binds faces the matrix. This more specific CC annotation is supported by structural data and functional characterization. While "mitochondrion" is annotated, the matrix localization should be explicitly noted. Supporting Evidence: PMID:12110673 IF(1) could be co-isolated with F(1)F(0) when the immunocapture procedure was carried out at pH 6.5 |
Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)