UQCRFS1 encodes the Rieske iron-sulfur protein (RISP), one of three catalytic subunits of the mitochondrial cytochrome bc1 complex (Complex III, CIII2). UQCRFS1 contains a [2Fe-2S] cluster that is essential for electron transfer from ubiquinol to cytochrome c1 during the Q-cycle. The protein is nuclear-encoded, imported into mitochondria, and inserted as the penultimate subunit during CIII assembly via BCS1L-mediated translocation. The catalytic globular domain resides in the intermembrane space, attached to the complex by a single transmembrane helix. After insertion, the N-terminal mitochondrial targeting sequence is cleaved to generate subunit 9, a small fragment that remains associated with the complex. Bi-allelic pathogenic variants cause mitochondrial Complex III deficiency (MC3DN10) with cardiomyopathy, alopecia totalis, and lactic acidosis (PMID:31883641). Deep research review (UQCRFS1-deep-research-falcon.md) confirms UQCRFS1 as a late-incorporating catalytic subunit essential for Q-cycle chemistry and ROS control, with assembly depending on LYRM7 and BCS1L. Recent in situ cryo-EM structures have directly visualized the Rieske head domain movement during catalytic electron transfer (Zheng et al. 2024, Nature).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016491 oxidoreductase activity | IBA GO_REF:0000033 | MODIFY | Summary: IBA annotation for oxidoreductase activity. UQCRFS1 is a catalytic subunit of Complex III that participates in oxidoreduction during the Q-cycle, transferring electrons from ubiquinol to cytochrome c1 via its [2Fe-2S] cluster (PMID:28380382). This term is correct but very broad. The more specific molecular function of UQCRFS1 as an individual subunit is electron transfer activity (GO:0009055), while the whole-complex activity is quinol-cytochrome-c reductase activity (GO:0008121). Since oxidoreductase activity is a parent of both of these, and the IBA inference is phylogenetically sound, this annotation is acceptable but could be made more specific. Deep research (UQCRFS1-deep-research-falcon.md) confirms the Rieske protein accepts an electron at the Qo site via its 2Fe-2S cluster and undergoes head-domain movement during the Q-cycle. Reason: UQCRFS1 is indeed an oxidoreductase as part of Complex III, but this term is too broad for informative annotation. The subunit-specific molecular function is electron transfer activity (GO:0009055) -- the Rieske protein transfers electrons via its [2Fe-2S] cluster from ubiquinol at the Qo site to cytochrome c1. This is well established from structural and biochemical studies (PMID:28380382). GO:0016491 is a valid parent term but does not convey the specific mechanism. Proposed replacements: electron transfer activity Supporting Evidence: PMID:28380382 The iron-sulfur (Fe-S) cluster of the Rieske protein, UQCRFS1, is essential for Complex III (CIII) activity, though the mechanism for Fe-S cluster transfer has not previously been elucidated. PMID:28380382 Energy transduction by Complex III (CIII) follows the Q cycle mechanism, whereby oxidation of a membrane-localized ubiquinol is coupled to proton pumping across the inner mitochondrial membrane into the intermembrane space. file:human/UQCRFS1/UQCRFS1-deep-research-falcon.md Deep research review confirms UQCRFS1 as the Rieske iron-sulfur protein participating in ubiquinol oxidation at the Qo site during the Q-cycle, with recent in situ cryo-EM resolving head-domain movements. |
| GO:0045275 respiratory chain complex III | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for respiratory chain complex III. UQCRFS1 is a core catalytic subunit of Complex III. The GO definition of respiratory chain complex III (GO:0045275) explicitly names the Rieske iron sulfur protein as one of the three catalytic subunits. This is firmly established across multiple lines of evidence including direct biochemical studies (PMID:23168492), disease genetics (PMID:31883641), and cryo-EM structures (PDB:5XTE). Reason: This is a core annotation. UQCRFS1 is unambiguously a structural component of respiratory chain complex III. The GO term definition explicitly names the Rieske ISP as one of the three catalytic subunits. Multiple experimental studies confirm this localization. Supporting Evidence: PMID:23168492 human LYRM7, which we propose to be renamed MZM1L (MZM1-like), works as a human Rieske Fe-S protein (UQCRFS1) chaperone, binding to this subunit within the mitochondrial matrix and stabilizing it prior to its translocation and insertion into the late CIII dimeric intermediate within the mitochondrial inner membrane. PMID:31883641 Here we describe rare bi-allelic variants in the gene of a catalytic subunit of CIII, UQCRFS1, which encodes the Rieske iron-sulfur protein, in two unrelated individuals. |
| GO:0006122 mitochondrial electron transport, ubiquinol to cytochrome c | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for the core biological process of UQCRFS1. This is the precise biological process catalyzed by Complex III, and UQCRFS1 is one of the three catalytic subunits directly involved in this electron transfer step. The Rieske protein accepts an electron from ubiquinol at the Qo site and transfers it to cytochrome c1 via its [2Fe-2S] cluster (PMID:28380382). Reason: This is the core biological process for UQCRFS1. The Rieske protein is one of three catalytic subunits of Complex III that directly participates in electron transfer from ubiquinol to cytochrome c. This is the most specific and accurate BP annotation for this gene. Phylogenetic inference is well supported. Supporting Evidence: PMID:28380382 Ubiquinol-cytochrome c oxidoreductase (E.C. 1.10.2.2, also known as cytochrome bc1 complex or Complex III), a central component of the mitochondrial respiratory chain, consists of 11 different subunits |
| GO:1902600 proton transmembrane transport | IEA GO_REF:0000108 | KEEP AS NON CORE | Summary: IEA annotation inferred from quinol-cytochrome-c reductase activity (GO:0008121) via logical inference. Complex III couples electron transfer to proton translocation across the inner mitochondrial membrane during the Q-cycle (PMID:28380382). UQCRFS1 contributes to this activity as a catalytic subunit, though the proton translocation itself is primarily mediated through the quinone chemistry in cytochrome b rather than the Rieske protein directly. Reason: Proton transmembrane transport is a downstream consequence of the Q-cycle catalyzed by Complex III as a whole. UQCRFS1 contributes to the overall Q-cycle mechanism but proton translocation is more directly attributable to the quinone chemistry at the Qo and Qi sites of cytochrome b. This is an IEA inference from the whole-complex activity and is not wrong but is not the core function of the Rieske subunit specifically. Supporting Evidence: PMID:28380382 Energy transduction by Complex III (CIII) follows the Q cycle mechanism, whereby oxidation of a membrane-localized ubiquinol is coupled to proton pumping across the inner mitochondrial membrane into the intermembrane space. |
| GO:0005743 mitochondrial inner membrane | IEA GO_REF:0000044 | ACCEPT | Summary: IEA annotation from UniProt subcellular location mapping. UQCRFS1 is an integral membrane protein of the mitochondrial inner membrane with a single transmembrane helix (residues 104-140, PDB:5XTE). UniProt explicitly annotates the subcellular location as mitochondrion inner membrane. This is well established. Reason: UQCRFS1 is an integral single-pass membrane protein of the mitochondrial inner membrane, confirmed by cryo-EM structures (PDB:5XTE) and UniProt annotation. The IEA mapping is correct and consistent with experimental evidence. |
| GO:0008121 quinol-cytochrome-c reductase activity | IEA GO_REF:0000120 | MODIFY | Summary: IEA annotation for the whole-complex enzymatic activity of Complex III (EC 7.1.1.8). UQCRFS1 is one of three catalytic subunits of Complex III that together catalyze the quinol-cytochrome-c reductase reaction. However, as a single subunit, UQCRFS1 does not independently catalyze this full reaction -- it contributes to the complex activity. In GO annotation practice, individual subunits of a complex should use the contributes_to qualifier for the whole-complex activity. The more specific subunit-level MF is electron transfer activity (GO:0009055). Reason: This annotation is correct in substance -- UQCRFS1 is a catalytic subunit of the complex that performs this reaction. However, the GOA file shows this with the enables qualifier, and UQCRFS1 alone cannot catalyze the full quinol-cytochrome-c reductase reaction. The subunit-specific MF is electron transfer activity, while GO:0008121 should be retained only as a contributes_to activity of Complex III. Proposed replacements: electron transfer activity Supporting Evidence: PMID:28380382 The catalytic activity of CIII depends on three highly conserved subunits that contain redox active centers, cytochrome b (MT-CYB), cytochrome c 1 (CYC1), and the Rieske iron-sulfur |
| GO:0016020 membrane | IEA GO_REF:0000002 | ACCEPT | Summary: IEA annotation from InterPro domain mapping. UQCRFS1 has a single transmembrane helix (residues 104-140) and is an integral membrane protein. This term is correct but extremely generic. More specific terms (mitochondrial inner membrane, GO:0005743) are already annotated from other sources. Reason: This is a correct but very generic CC annotation. UQCRFS1 is indeed a membrane protein with a transmembrane helix. More specific annotations (mitochondrial inner membrane) are present from other evidence lines. As a broad IEA it is acceptable to retain, though it adds little information beyond what is captured by the more specific terms. |
| GO:0022904 respiratory electron transport chain | IEA GO_REF:0000043 | ACCEPT | Summary: IEA annotation from UniProt keyword mapping (KW-0679, Respiratory chain). UQCRFS1 is a core component of the mitochondrial respiratory electron transport chain as a catalytic subunit of Complex III. This is correct and well supported, though the more specific child term GO:0006122 (mitochondrial electron transport, ubiquinol to cytochrome c) is the precise process. Reason: This is a correct and broader parent annotation. UQCRFS1 unambiguously participates in the respiratory electron transport chain. The more specific term GO:0006122 is already annotated via IBA. As an IEA from keyword mapping, this broader annotation is acceptable. |
| GO:0031966 mitochondrial membrane | IEA GO_REF:0000117 | ACCEPT | Summary: IEA annotation from ARBA machine learning model. UQCRFS1 is located in the mitochondrial inner membrane specifically. This term (mitochondrial membrane) is a parent of mitochondrial inner membrane (GO:0005743), which is already annotated. Correct but less informative. Reason: Correct but generic. UQCRFS1 is specifically in the mitochondrial inner membrane, and the more specific term GO:0005743 is already annotated from multiple sources. This broader IEA is acceptable to retain. |
| GO:0045275 respiratory chain complex III | IEA GO_REF:0000117 | ACCEPT | Summary: IEA annotation from ARBA for respiratory chain complex III. Duplicate of the IBA annotation with the same GO ID. UQCRFS1 is unambiguously a subunit of Complex III. Both annotations (IBA and IEA) are valid. Reason: Correct. This duplicates the IBA annotation for the same term, which is fine -- independent evidence lines supporting the same conclusion. UQCRFS1 is a core catalytic subunit of respiratory chain complex III. |
| GO:0046872 metal ion binding | IEA GO_REF:0000043 | ACCEPT | Summary: IEA annotation from UniProt keyword mapping (KW-0479, Iron). UQCRFS1 binds iron as part of its [2Fe-2S] cluster. This term is correct but very broad. The more specific term GO:0051537 (2 iron, 2 sulfur cluster binding) is already annotated and is far more informative. Reason: Correct but very generic. UQCRFS1 does bind metal ions (iron in its [2Fe-2S] cluster). The more specific child term GO:0051537 is already annotated from other sources. As a broad IEA from keyword mapping, this is acceptable to retain, though it provides minimal additional information. |
| GO:0051536 iron-sulfur cluster binding | IEA GO_REF:0000043 | ACCEPT | Summary: IEA annotation from UniProt keyword mapping (KW-0411, Iron-sulfur). UQCRFS1 binds a [2Fe-2S] cluster, which is a type of iron-sulfur cluster. Correct but less specific than GO:0051537 (2 iron, 2 sulfur cluster binding) which is already annotated. Reason: Correct. UQCRFS1 binds an iron-sulfur cluster (specifically [2Fe-2S]). The more specific child term GO:0051537 is already present. This broader IEA is acceptable. |
| GO:0051537 2 iron, 2 sulfur cluster binding | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation from combined automated methods. UQCRFS1 binds a single [2Fe-2S] cluster per subunit, coordinated by Cys217, Cys219, Cys236, His239, and His241 in the Rieske domain (UniProt FT BINDING entries). This is a well-characterized cofactor essential for the electron transfer function of UQCRFS1 (PMID:28380382). Reason: Core molecular function annotation. UQCRFS1 binds one [2Fe-2S] cluster per subunit, which is essential for its electron transfer activity. This is confirmed by the UniProt record, structural data, and multiple experimental studies. The IEA annotation is correct and well supported. Supporting Evidence: PMID:28380382 The iron-sulfur (Fe-S) cluster of the Rieske protein, UQCRFS1, is essential for Complex III (CIII) activity |
| GO:0005515 protein binding | IPI PMID:27499296 Mitochondrial Protein Interaction Mapping Identifies Regulat... | MARK AS OVER ANNOTATED | Summary: IPI annotation for protein binding based on mitochondrial protein interaction mapping study (Floyd et al. 2016). The GOA WITH/FROM column shows UniProtKB:Q5U5X0 (LYRM7). LYRM7 is a well-characterized UQCRFS1 chaperone that stabilizes the apo-Rieske protein in the mitochondrial matrix prior to [2Fe-2S] cluster insertion and BCS1L-mediated translocation into Complex III (PMID:23168492, PMID:28380382). This is a real interaction but protein binding is uninformative. Reason: The UQCRFS1-LYRM7 interaction is genuine and functionally important -- LYRM7 chaperones UQCRFS1 during Complex III assembly. However, protein binding (GO:0005515) conveys no useful functional information about this interaction. Per GO curation guidelines, protein binding should be avoided when more specific terms are available. The interaction is better captured by the assembly process annotation (GO:0034551) and CC annotations. Supporting Evidence: PMID:27499296 we assessed condition-specific protein-protein interactions for 50 select MXPs using affinity enrichment mass spectrometry. Our data connect MXPs to diverse mitochondrial processes, including multiple aspects of respiratory chain function. |
| GO:0005515 protein binding | IPI PMID:28380382 A Single Adaptable Cochaperone-Scaffold Complex Delivers Nas... | MARK AS OVER ANNOTATED | Summary: IPI annotation for protein binding from Maio et al. 2017 (Cell Metab). WITH/FROM is Q5U5X0 (LYRM7). This study demonstrated that LYRM7 directly binds UQCRFS1 in a pre-assembly intermediate and recruits the Fe-S transfer complex (HSC20/HSPA9/ISCU) for [2Fe-2S] cluster delivery. The interaction is mechanistically important but protein binding is uninformative. Reason: Same interaction as above (UQCRFS1-LYRM7), confirmed with more mechanistic detail in this study. Protein binding does not capture the functional significance. The interaction is part of the Fe-S cluster biogenesis and Complex III assembly pathway. Better captured by other annotations. Supporting Evidence: PMID:28380382 a transient subcomplex involved in CIII assembly, composed of LYRM7 bound to UQCRFS1, interacts with components of an Fe-S transfer complex, consisting of HSC20, its cognate chaperone HSPA9, and the holo-scaffold ISCU. |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | MARK AS OVER ANNOTATED | Summary: IPI annotation for protein binding from Huttlin et al. 2021 (Cell), the BioPlex 3.0 proteome-scale interaction network. WITH/FROM is Q5U5X0 (LYRM7). This is a high-throughput interactome study that independently detected the UQCRFS1-LYRM7 interaction via affinity purification mass spectrometry. The interaction is genuine but this is the same interaction already captured by more focused studies. Reason: Same UQCRFS1-LYRM7 interaction detected in a high-throughput interactome screen. Protein binding remains uninformative. The functional significance of this interaction is better captured by assembly process annotations. Supporting Evidence: PMID:33961781 Through affinity-purification mass spectrometry, we have created two proteome-scale, cell-line-specific interaction networks. |
| GO:0005515 protein binding | IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func... | MARK AS OVER ANNOTATED | Summary: IPI annotation for protein binding from Schaffer et al. 2025 (Nature), multimodal cell maps. WITH/FROM is Q5U5X0 (LYRM7). Another independent detection of the UQCRFS1-LYRM7 interaction in a large-scale study. Reason: Same UQCRFS1-LYRM7 interaction. Protein binding is uninformative per GO curation guidelines. The functional context (chaperone interaction during Complex III assembly) is not captured by this generic term. Supporting Evidence: PMID:40205054 we construct a global map of human subcellular architecture through joint measurement of biophysical interactions and immunofluorescence images for over 5,100 proteins in U2OS osteosarcoma cells. |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | ACCEPT | Summary: HTP annotation for mitochondrial localization from Morgenstern et al. 2021 (Cell Metab), a quantitative high-confidence human mitochondrial proteome study. UQCRFS1 is unambiguously a mitochondrial protein -- it is a core subunit of mitochondrial Complex III. This is well established. Reason: UQCRFS1 is a bona fide mitochondrial protein, confirmed by multiple independent experimental approaches. This HTP annotation from a high-quality mitochondrial proteome study is correct, though more specific CC annotations (mitochondrial inner membrane, respiratory chain complex III) are also present. Supporting Evidence: PMID:34800366 We classified >8,000 proteins in mitochondrial preparations of human cells and defined a mitochondrial high-confidence proteome of >1,100 proteins (MitoCoP). |
| GO:0045275 respiratory chain complex III | IDA PMID:23168492 LYRM7/MZM1L is a UQCRFS1 chaperone involved in the last step... | ACCEPT | Summary: IDA annotation for Complex III localization from Sanchez et al. 2013 (BBA). This study characterized LYRM7 as a UQCRFS1 chaperone and in the process directly demonstrated UQCRFS1 incorporation into the Complex III dimer by BN-PAGE and immunodetection. UQCRFS1 was shown to co-migrate with assembled CIII2 and supercomplexes. Reason: Direct experimental evidence (IDA) for UQCRFS1 as part of Complex III. The study used BN-PAGE to demonstrate UQCRFS1 incorporation into assembled Complex III. This is a core CC annotation with strong experimental support. Supporting Evidence: PMID:23168492 LYRM7/MZM1L is a novel human CIII assembly factor involved in the UQCRFS1 insertion step, which enables formation of the mature and functional CIII enzyme. |
| GO:0045275 respiratory chain complex III | IC PMID:31883641 Bi-Allelic UQCRFS1 Variants Are Associated with Mitochondria... | ACCEPT | Summary: IC (inferred by curator) annotation for Complex III membership from Gusic et al. 2020 (Am J Hum Genet). The GOA WITH/FROM column shows GO:0034551 (mitochondrial respiratory chain complex III assembly), indicating the curator inferred Complex III membership from assembly defects observed in patient fibroblasts with UQCRFS1 variants. Patient cells showed reduced UQCRFS1 abundance and impaired CIII assembly. Reason: Valid curator inference. If UQCRFS1 variants impair Complex III assembly and reduce CIII activity, it follows that UQCRFS1 is part of Complex III. This is well supported by the disease genetics study and consistent with all other evidence. Supporting Evidence: PMID:31883641 Studies in proband-derived fibroblasts showed a deleterious effect of the variants on UQCRFS1 protein abundance, mitochondrial import, CIII assembly, and cellular respiration. |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-9866272 | ACCEPT | Summary: TAS annotation from Reactome pathway R-HSA-9866272 (2Fe-2S is inserted in UQCRFS1). This Reactome reaction models the [2Fe-2S] cluster insertion step during UQCRFS1 maturation, which occurs at the mitochondrial inner membrane. UQCRFS1 is indeed located in the inner membrane after assembly. Reason: Correct. UQCRFS1 is a single-pass integral protein of the mitochondrial inner membrane. The Reactome annotation from the Fe-S cluster insertion pathway is consistent with the known biology. |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-9906017 | ACCEPT | Summary: TAS annotation from Reactome pathway R-HSA-9906017 (Unknown peptidase cleaves UQCRFS1 subunit). This reaction models the proteolytic processing of UQCRFS1 after its insertion into Complex III at the inner membrane. The localization is correct. Reason: Correct. The proteolytic processing of UQCRFS1 occurs after its insertion into the inner membrane Complex III dimer. |
| GO:0005759 mitochondrial matrix | TAS Reactome:R-HSA-9866253 | KEEP AS NON CORE | Summary: TAS annotation from Reactome pathway R-HSA-9866253 (apo-UQCRFS1 binds LYRM7). This reaction models the chaperone binding step where apo-UQCRFS1 binds LYRM7 in the mitochondrial matrix prior to Fe-S cluster insertion and BCS1L-mediated translocation. The matrix is the transient location of the apo-protein during assembly, not the final functional location. Reason: Correct but non-core for the assembly intermediate. After import into mitochondria, apo-UQCRFS1 resides transiently in the mitochondrial matrix where it binds LYRM7 and receives its [2Fe-2S] cluster before being translocated by BCS1L into the pre-CIII complex in the inner membrane. The final functional location is the mitochondrial inner membrane, so matrix localization should not be treated as a core active location. Supporting Evidence: PMID:28380382 Binding of HSC20 to the LYR motif of LYRM7 in a pre-assembled UQCRFS1-LYRM7 intermediate in the mitochondrial matrix facilitates Fe-S cluster transfer to UQCRFS1. PMID:23168492 binding to this subunit within the mitochondrial matrix and stabilizing it prior to its translocation and insertion into the late CIII dimeric intermediate within the mitochondrial inner membrane. |
| GO:0005759 mitochondrial matrix | TAS Reactome:R-HSA-9866272 | KEEP AS NON CORE | Summary: TAS annotation from Reactome pathway R-HSA-9866272 (2Fe-2S is inserted in UQCRFS1). This reaction occurs in the mitochondrial matrix where the Fe-S transfer complex delivers the [2Fe-2S] cluster to apo-UQCRFS1 bound to LYRM7. As above, matrix localization is a transient assembly state. Reason: Correct but non-core for the assembly intermediate. The Fe-S cluster insertion into UQCRFS1 occurs in the mitochondrial matrix via the HSC20/HSPA9/ISCU transfer complex. This is a valid transient localization during UQCRFS1 biogenesis, but the final functional location is the mitochondrial inner membrane. Supporting Evidence: PMID:28380382 Binding of HSC20 to the LYR motif of LYRM7 in a pre-assembled UQCRFS1-LYRM7 intermediate in the mitochondrial matrix facilitates Fe-S cluster transfer to UQCRFS1. |
| GO:0005739 mitochondrion | IDA PMID:31883641 Bi-Allelic UQCRFS1 Variants Are Associated with Mitochondria... | ACCEPT | Summary: IDA annotation for mitochondrial localization from Gusic et al. 2020. This study showed that wild-type UQCRFS1 localizes to mitochondria, and the V14D pathogenic variant causes mislocalization to the cytosol and nucleus. Direct immunofluorescence microscopy confirmed the mitochondrial localization of wild-type UQCRFS1. Reason: Direct experimental demonstration that UQCRFS1 localizes to mitochondria. The disease study provided direct evidence via immunofluorescence showing mitochondrial localization of the wild-type protein and mislocalization of the V14D mutant. Supporting Evidence: PMID:31883641 Studies in proband-derived fibroblasts showed a deleterious effect of the variants on UQCRFS1 protein abundance, mitochondrial import, CIII assembly, and cellular respiration. |
| GO:0022904 respiratory electron transport chain | IMP PMID:31883641 Bi-Allelic UQCRFS1 Variants Are Associated with Mitochondria... | ACCEPT | Summary: IMP annotation for respiratory electron transport chain from Gusic et al. 2020. Bi-allelic UQCRFS1 variants caused impaired cellular respiration in patient fibroblasts, which was rescued by lentiviral complementation with wild-type UQCRFS1. This demonstrates that UQCRFS1 is required for respiratory chain function. Reason: Valid IMP annotation. The mutant phenotype (impaired cellular respiration) directly demonstrates involvement in the respiratory electron transport chain. Complementation with wild-type UQCRFS1 rescued the defect, confirming causality. This is also a parent term of GO:0006122 which is the more specific annotation. Supporting Evidence: PMID:31883641 Complementation studies via lentiviral transduction and overexpression of wild-type UQCRFS1 restored mitochondrial function and rescued the cellular phenotype, confirming UQCRFS1 variants as causative for CIII deficiency. |
| GO:0034551 mitochondrial respiratory chain complex III assembly | IMP PMID:31883641 Bi-Allelic UQCRFS1 Variants Are Associated with Mitochondria... | KEEP AS NON CORE | Summary: IMP annotation for Complex III assembly from Gusic et al. 2020. Patient fibroblasts with bi-allelic UQCRFS1 variants showed impaired CIII assembly by BN-PAGE. UQCRFS1 is the penultimate subunit incorporated during CIII assembly, so its loss directly impairs the assembly process. This is a real involvement but is not the core evolved function of the Rieske protein -- the core function is electron transfer. Reason: UQCRFS1 is incorporated as the penultimate step in Complex III assembly, and its loss impairs CIII assembly. However, UQCRFS1 is not an assembly factor per se -- it is a structural/catalytic subunit whose incorporation is required for full assembly. The assembly process is better attributed to assembly factors like BCS1L, LYRM7, and TTC19. The annotation is correct (UQCRFS1 variants do disrupt assembly) but it describes a consequence of subunit loss rather than the core function of the protein. Supporting Evidence: PMID:31883641 Studies in proband-derived fibroblasts showed a deleterious effect of the variants on UQCRFS1 protein abundance, mitochondrial import, CIII assembly, and cellular respiration. PMID:28380382 Incorporation of the Rieske protein UQCRFS1 is the penultimate step in CIII assembly, followed only by the insertion of a small supernumerary subunit (UQCR10 in mammalian cells). |
| GO:0005515 protein binding | IPI PMID:23168492 LYRM7/MZM1L is a UQCRFS1 chaperone involved in the last step... | MARK AS OVER ANNOTATED | Summary: IPI annotation for protein binding from Sanchez et al. 2013 (BBA). WITH/FROM is Q5U5X0 (LYRM7). This study identified LYRM7 as a human UQCRFS1 chaperone. The interaction was demonstrated by co-purification and other biochemical approaches. The interaction is genuine and functionally important (LYRM7 stabilizes apo-UQCRFS1 in the matrix). Reason: Same UQCRFS1-LYRM7 interaction as the other IPI annotations. Protein binding is uninformative per GO guidelines. The functional significance of this chaperone interaction is better captured by the assembly-related annotations. Supporting Evidence: PMID:23168492 We conclude that human LYRM7, which we propose to be renamed MZM1L (MZM1-like), works as a human Rieske Fe-S protein (UQCRFS1) chaperone |
| GO:0005739 mitochondrion | HDA PMID:20833797 Phosphoproteome analysis of functional mitochondria isolated... | ACCEPT | Summary: HDA (high-throughput direct assay) annotation for mitochondrial localization from Zhao et al. 2011 (Mol Cell Proteomics). This phosphoproteomics study isolated functional mitochondria from human skeletal muscle and identified UQCRFS1 among the mitochondrial phosphoproteins by mass spectrometry. Reason: Correct. UQCRFS1 was identified by mass spectrometry in purified mitochondrial fractions from human skeletal muscle. This is consistent with all other evidence for mitochondrial localization. Supporting Evidence: PMID:20833797 We performed a phosphoproteomics study of functional mitochondria isolated from human muscle biopsies with the aim to obtain a comprehensive overview of mitochondrial phosphoproteins. |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-164651 | ACCEPT | Summary: TAS annotation from Reactome pathway R-HSA-164651 (Electron transfer from ubiquinol to cytochrome c of complex III). This reaction represents the core catalytic function of Complex III occurring at the inner membrane, where UQCRFS1 participates as the Rieske iron-sulfur subunit. Reason: Correct. UQCRFS1 functions at the mitochondrial inner membrane as part of Complex III during electron transfer from ubiquinol to cytochrome c. This Reactome pathway correctly models the functional localization. |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-9906042 | ACCEPT | Summary: TAS annotation from Reactome pathway R-HSA-9906042 (TTC19 clears UQCRFS1 fragments from Complex III). This reaction models the quality control step where TTC19 removes UQCRFS1-derived fragments from the inner membrane Complex III. The localization is correct. Reason: Correct. The TTC19-mediated clearance of UQCRFS1 fragments occurs at the mitochondrial inner membrane where Complex III resides. This is consistent with the known biology of UQCRFS1 processing. |
| GO:0009055 electron transfer activity | ISS PMID:28380382 A Single Adaptable Cochaperone-Scaffold Complex Delivers Nas... | NEW | Summary: NEW annotation. UQCRFS1 is the Rieske iron-sulfur protein that transfers electrons from ubiquinol (at the Qo site of cytochrome b) to cytochrome c1 via its [2Fe-2S] cluster. This is the subunit-specific molecular function that is missing from the current annotation set. The existing annotations include the whole-complex activity (GO:0008121, quinol-cytochrome-c reductase activity) and the broad parent (GO:0016491, oxidoreductase activity), but the specific electron transfer activity of the Rieske subunit is not captured. Deep research (UQCRFS1-deep-research-falcon.md) confirms that in situ cryo-EM structures captured the Rieske head domain positions across catalytic states during the Q-cycle (Zheng et al. 2024, Nature). Reason: The existing annotations lack a subunit-specific MF term for UQCRFS1. Electron transfer activity (GO:0009055) precisely describes what the Rieske protein does -- it transfers electrons between ubiquinol and cytochrome c1 using its [2Fe-2S] cluster. This is well established from structural and biochemical studies and is the most informative MF annotation for this subunit. Supporting Evidence: PMID:28380382 The iron-sulfur (Fe-S) cluster of the Rieske protein, UQCRFS1, is essential for Complex III (CIII) activity |
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Download this section (compressed HTML)Q: What controls the kinetics and timing of the Rieske head-domain swing between the b-position (electron acceptance from ubiquinol at the Qo site) and the c-position (electron donation to cytochrome c1) during the Q-cycle, and how is this coupled to proton translocation in human Complex III?
Q: How is the LYRM7-bound apo-UQCRFS1 intermediate handed off to the HSC20/HSPA9/ISCU Fe-S transfer complex, and what determines the order of Fe-S cluster insertion versus BCS1L-mediated translocation into the inner membrane Complex III pre-assembly?
Q: What is the role of the cleaved N-terminal peptide (subunit 9/UQCR11) and its TTC19-mediated turnover in stabilising the mature Complex III dimer, and does its accumulation contribute to disease in TTC19-deficient patients?
Q: How do disease-associated UQCRFS1 variants (e.g. V14D, R63H) selectively impair mitochondrial import, [2Fe-2S] cluster acquisition, or BCS1L translocation, and which step is rate-limiting in the tissue-specific cardiomyopathy and alopecia phenotype?
Experiment: Reconstitute the human apo-UQCRFS1/LYRM7/HSC20/HSPA9/ISCU Fe-S transfer pathway in vitro with purified components and chemically reconstituted [2Fe-2S] donors, then measure cluster transfer kinetics by EPR/UV-vis under wild-type versus disease-mutant conditions to identify the rate-limiting transfer step.
Experiment: Use BCS1L-overexpression and CRISPR-engineered UQCRFS1 variant cell lines to follow Rieske-protein translocation kinetics across the inner membrane by pulse-chase split-fluorescent-protein complementation, distinguishing import, matrix folding, Fe-S insertion, and BCS1L-driven translocation defects.
Experiment: Capture in situ time-resolved cryo-electron tomography of mitochondrial cristae from human cardiomyocytes carrying UQCRFS1 disease variants to determine whether Rieske head-domain swing is impaired or whether Complex III/IV supercomplex architecture is altered.
Experiment: Generate a UQCRFS1 conditional-knockout/rescue mouse model with tissue-restricted expression of WT versus catalytically dead Rieske variants to dissect the contribution of electron transfer activity versus structural assembly support to the cardiomyopathy and alopecia phenotype.
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