NDUFS2

---
id: O75306
gene_symbol: NDUFS2
product_type: PROTEIN
status: IN_PROGRESS
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  NDUFS2 encodes the 49 kDa subunit of mitochondrial Complex I (NADH:ubiquinone oxidoreductase,
  EC 7.1.1.2), and is a core catalytic subunit of the Q-module in the peripheral (matrix-facing)
  arm. NDUFS2 directly contributes to the ubiquinone-binding channel, providing the
  conserved
  His59/Tyr108 residue pair that contacts and orients the ubiquinone headgroup during
  reduction.
  It binds one [4Fe-4S] cluster and is essential for both Complex I assembly and catalytic
  activity.
  NDUFS2 is dimethylated at Arg-85 (Arg-118 in precursor numbering) by the assembly
  factor NDUFAF7,
  a modification required for stabilization of early assembly intermediates. NDUFS2
  is also a
  redox-sensitive component implicated in acute oxygen sensing in pulmonary artery
  smooth muscle
  cells, where its cysteine residues become reduced under hypoxia, inhibiting Complex
  I and
  triggering hypoxic pulmonary vasoconstriction. Pathogenic mutations cause mitochondrial
  Complex I
  deficiency (MC1DN6, presenting as Leigh syndrome) and Leber-like hereditary optic
  neuropathy
  (LHONAR2).
alternative_products:
  - name: '1'
    id: O75306-1
  - name: '2'
    id: O75306-2
    sequence_note: VSP_046466
existing_annotations:
# ============================================================
# IBA ANNOTATIONS (phylogenetic inference from GO_Central)
# ============================================================
  - term:
      id: GO:0005743
      label: mitochondrial inner membrane
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: >-
        IBA annotation for mitochondrial inner membrane localization. NDUFS2 is a
        core
        subunit
        of Complex I which is anchored in the inner mitochondrial membrane. NDUFS2
        resides
        in the
        peripheral arm at the junction with the membrane arm, on the matrix side,
        as
        confirmed by
        cryo-EM structures (PMID:28844695). The phylogenetic inference is sound and
        consistent
        with all experimental evidence.
      action: ACCEPT
      reason: >-
        NDUFS2 is an integral component of Complex I which is embedded in the mitochondrial
        inner
        membrane. The IBA annotation is phylogenetically well-supported and experimentally
        confirmed
        by cryo-EM structural studies and immunodetection.
      supported_by:
        - reference_id: PMID:28844695
          supporting_text: >-
            The MCI2III2IV2 forms a circular structure with the dimeric CIII located
            in
            the center,
            where it is surrounded by two copies each of CI and CIV
        - reference_id: PMID:9585441
          supporting_text: >-
            Mapping to 1q23 of the human gene (NDUFS2) encoding the 49-kDa subunit
            of
            the
            mitochondrial respiratory Complex I and immunodetection of the mature
            protein
            in
            mitochondria
  - term:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: contributes_to
    review:
      summary: >-
        IBA annotation with 'contributes_to' qualifier for the complex-level NADH
        dehydrogenase
        (ubiquinone) activity (EC 7.1.1.2). NDUFS2 is a core catalytic subunit that
        forms the
        ubiquinone-binding channel with its conserved His59/Tyr108 residue pair, directly
        participating in ubiquinone reduction. The 'contributes_to' qualifier is correct
        because
        the full reaction (NADH + ubiquinone + 5H+_in -> NAD+ + ubiquinol + 4H+_out)
        requires
        the entire 45-subunit complex. Multiple studies demonstrate that NDUFS2 mutations
        impair
        Complex I catalytic activity (PMID:22036843, PMID:28031252, PMID:30922174).
      action: ACCEPT
      reason: >-
        Core function of NDUFS2. The 'contributes_to' qualifier is appropriate because
        NDUFS2
        is a subunit of the multi-subunit Complex I holoenzyme. NDUFS2 is particularly
        critical
        because it contains the ubiquinone-binding site, making it essential for catalysis.
        The IBA is phylogenetically sound and strongly supported experimentally.
      supported_by:
        - reference_id: PMID:22036843
          supporting_text: >-
            Complex I amounts in the patient carrying the Asp446Asn mutation were
            normal,
            while
            the complex I activity was strongly reduced, showing that the NDUFS2 mutation
            affects
            complex I enzymatic function
        - reference_id: PMID:30922174
          supporting_text: >-
            In PASMC, siNdufs2 (cells/tissue treated with Ndufs2 siRNA) decreased
            normoxic
            H2O2, prevented hypoxic increases in [Ca2+]i, and
            mimicked aspects of chronic hypoxia, including decreasing Complex I activity,
            elevating the nicotinamide adenine dinucleotide (NADH/NAD+) ratio
        - reference_id: file:human/NDUFS2/NDUFS2-deep-research-falcon.md
          supporting_text: >-
            NDUFS2 is a catalytic/structural subunit of complex I embedded in the
            matrix-arm
            Q-module, shaping the Q-channel where NADH-derived electrons (via FMN
            and
            Fe-S
            clusters to N2) reduce ubiquinone
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: >-
        IBA annotation for localization to respiratory chain complex I. NDUFS2 is
        a
        core subunit
        of Complex I, identified as a component of the immunopurified human NADH dehydrogenase
        (PMID:12611891). This is a fundamental and unambiguous annotation for NDUFS2.
      action: ACCEPT
      reason: >-
        Core CC annotation. NDUFS2 is an integral, well-established subunit of respiratory
        chain Complex I. The IBA is phylogenetically well-supported and confirmed
        by
        multiple
        experimental studies including mass spectrometry identification and cryo-EM
        structures.
      supported_by:
        - reference_id: PMID:12611891
          supporting_text: >-
            we can resolve and identify the human homologues of 42 polypeptides detected
            so far
            in the more extensively studied beef heart complex I
  - term:
      id: GO:0006120
      label: mitochondrial electron transport, NADH to ubiquinone
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: >-
        IBA annotation for the biological process of mitochondrial electron transport
        from
        NADH to ubiquinone. As a core catalytic subunit of Complex I that directly
        contributes
        to the ubiquinone-binding site and reduction, NDUFS2 is centrally involved
        in
        this process.
        Knockdown of NDUFS2 impairs Complex I-dependent electron transport (PMID:30922174).
      action: ACCEPT
      reason: >-
        Core biological process for NDUFS2. The protein is essential for the catalytic
        cycle
        of Complex I, directly participating in ubiquinone reduction. The IBA is well-supported
        phylogenetically and experimentally.
      supported_by:
        - reference_id: PMID:30922174
          supporting_text: >-
            In PASMC, siNdufs2 (cells/tissue treated with Ndufs2 siRNA) decreased
            normoxic
            H2O2, prevented hypoxic increases in [Ca2+]i, and
            mimicked aspects of chronic hypoxia, including decreasing Complex I activity,
            elevating the nicotinamide adenine dinucleotide (NADH/NAD+) ratio
        - reference_id: PMID:22036843
          supporting_text: >-
            the complex I activity was strongly reduced, showing that the NDUFS2 mutation
            affects complex I enzymatic function

# ============================================================
# IEA ANNOTATIONS (electronic/computational)
# ============================================================
  - term:
      id: GO:1902600
      label: proton transmembrane transport
    evidence_type: IEA
    original_reference_id: GO_REF:0000108
    review:
      summary: >-
        IEA annotation inferred from GO:0008137 (NADH dehydrogenase ubiquinone activity)
        via
        logical inference. Complex I couples electron transfer to proton translocation
        across
        the inner membrane. NDUFS2 does not directly participate in proton pumping,
        which is
        performed by the membrane arm subunits (ND2, ND4, ND5). However, the Q-site
        region
        where NDUFS2 resides is mechanistically coupled to the proton-pumping machinery
        via
        hydrated channels and the E-channel (Grba et al. 2023, Sci Adv). As an IEA
        for
        a
        Complex I subunit, this is acceptable as a broader process annotation.
      action: ACCEPT
      reason: >-
        While proton translocation is performed by the membrane arm, this is a legitimate
        broader process annotation for a Complex I subunit. The coupling between NDUFS2's
        Q-site and proton pumping is mechanistically real, though the annotation is
        not
        the most informative for NDUFS2 specifically.
  - term:
      id: GO:0005743
      label: mitochondrial inner membrane
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    review:
      summary: >-
        IEA annotation for mitochondrial inner membrane localization, consistent with
        the
        IBA annotation and cryo-EM structural data (PMID:28844695). NDUFS2 is a peripheral
        membrane protein on the matrix side of the inner membrane.
      action: ACCEPT
      reason: >-
        Correct localization, consistent with the IBA and experimental evidence. Redundant
        with the IBA but acceptable as an independent IEA line.
  - term:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    review:
      summary: >-
        IEA annotation for NADH dehydrogenase (ubiquinone) activity. Consistent with
        the
        IBA and multiple experimental annotations for this core function.
      action: ACCEPT
      reason: >-
        Correct MF annotation, consistent with IBA and experimental evidence. Redundant
        but acceptable as an independent IEA.
  - term:
      id: GO:0016491
      label: oxidoreductase activity
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: >-
        IEA annotation from UniProt keyword mapping. Oxidoreductase activity is a
        very
        broad
        parent term. NDUFS2 contributes to the oxidoreductase activity of Complex
        I
        (EC 7.1.1.2),
        specifically via the ubiquinone reduction step. This is a valid but non-informative
        parent of the more specific GO:0008137.
      action: ACCEPT
      reason: >-
        While very general, this is not wrong for an IEA. The more specific GO:0008137
        term
        is annotated separately. This broad IEA is acceptable as a parent-level annotation.
  - term:
      id: GO:0016651
      label: oxidoreductase activity, acting on NAD(P)H
    evidence_type: IEA
    original_reference_id: GO_REF:0000002
    review:
      summary: >-
        IEA from InterPro mapping. Complex I oxidizes NADH, so this parent term is
        technically
        applicable to the complex. However, NDUFS2 is in the Q-module and does not
        directly
        interact with NADH (the NADH-binding site is in the N-module on NDUFV1). This
        is a
        broad annotation that is more appropriate for the NADH-binding subunit NDUFV1
        than
        for NDUFS2.
      action: MODIFY
      reason: >-
        While Complex I as a whole acts on NADH, NDUFS2 specifically is in the Q-module
        and
        interacts with ubiquinone, not NADH. The NADH binding site is on NDUFV1 in
        the
        N-module.
        For NDUFS2 specifically, quinone binding (GO:0048038) is more appropriate.
        However,
        as an IEA from InterPro domain mapping to the Complex I 49kDa subunit family,
        it is
        not entirely wrong as a complex-level annotation. Should be modified to reflect
        NDUFS2's actual substrate interaction.
      proposed_replacement_terms:
        - id: GO:0048038
          label: quinone binding
  - term:
      id: GO:0022904
      label: respiratory electron transport chain
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: >-
        IEA from UniProt keyword mapping for the respiratory electron transport chain
        process.
        NDUFS2 is a core subunit of Complex I, the first complex of the respiratory
        chain.
        This is a valid broader process annotation.
      action: ACCEPT
      reason: >-
        Correct broader process annotation. Complex I is the entry point for NADH-derived
        electrons into the respiratory chain, and NDUFS2 is a core catalytic subunit.
        The more specific GO:0006120 is annotated separately.
  - term:
      id: GO:0046872
      label: metal ion binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: >-
        IEA from UniProt keyword mapping for metal ion binding. NDUFS2 binds one [4Fe-4S]
        cluster via three conserved cysteine residues (Cys326, Cys332, Cys347 in precursor
        numbering per UniProt). This is a valid but very broad annotation; the more
        specific
        GO:0051539 (4 iron, 4 sulfur cluster binding) is also annotated.
      action: ACCEPT
      reason: >-
        Correct but very general. NDUFS2 does bind iron via its [4Fe-4S] cluster.
        The
        more
        specific term GO:0051539 is also annotated. This broad IEA is acceptable.
  - term:
      id: GO:0048038
      label: quinone binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000002
    review:
      summary: >-
        IEA from InterPro mapping for quinone binding. NDUFS2 contains the ubiquinone-binding
        channel with the conserved His59/Tyr108 residue pair that directly contacts
        the quinone
        headgroup. This is a core molecular function of NDUFS2. A more specific child
        term
        GO:0048039 (ubiquinone binding) exists and would be more precise.
      action: MODIFY
      reason: >-
        NDUFS2 specifically binds ubiquinone (coenzyme Q), not quinones generically.
        The more
        specific term GO:0048039 (ubiquinone binding) would be more appropriate given
        the
        well-characterized structural evidence of NDUFS2 forming the ubiquinone-binding
        channel with His59/Tyr108 contacting the ubiquinone headgroup.
      proposed_replacement_terms:
        - id: GO:0048039
          label: ubiquinone binding
      supported_by:
        - reference_id: file:human/NDUFS2/NDUFS2-deep-research-falcon.md
          supporting_text: >-
            NDUFS2-His59 (His59) is a quinone/ligand-contacting residue implicated
            in
            H-bonding
            and stabilization of the quinone head; Tyr108 locates near the redox site
            and
            contributes to headgroup interactions
  - term:
      id: GO:0051287
      label: NAD binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000002
    review:
      summary: >-
        IEA from InterPro mapping for NAD binding. While Complex I as a whole binds
        and
        oxidizes NADH, the NADH-binding site is on NDUFV1 (51 kDa subunit) in the
        N-module,
        not on NDUFS2 in the Q-module. NDUFS2 does not directly bind NAD/NADH. This
        annotation
        appears to be an over-annotation arising from InterPro domain annotation of
        the
        broader Complex I family.
      action: REMOVE
      reason: >-
        NDUFS2 does not bind NAD or NADH. The NADH-binding site in Complex I is located
        on
        the NDUFV1 (51 kDa) subunit in the N-module, which also contains the FMN cofactor.
        NDUFS2 is in the Q-module and binds ubiquinone, not NADH. This IEA is likely
        a
        spurious transfer from the broader Complex I domain family annotation.
  - term:
      id: GO:0051536
      label: iron-sulfur cluster binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: >-
        IEA from UniProt keyword mapping for iron-sulfur cluster binding. NDUFS2 binds
        one
        [4Fe-4S] cluster. This is a valid parent term; the more specific GO:0051539
        is also
        annotated.
      action: ACCEPT
      reason: >-
        Correct annotation. NDUFS2 binds a [4Fe-4S] cluster. This is a valid broader
        term
        complementing the more specific GO:0051539 annotation.
  - term:
      id: GO:0051539
      label: 4 iron, 4 sulfur cluster binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: >-
        IEA from UniProt keyword mapping. NDUFS2 binds one [4Fe-4S] cluster via three
        conserved cysteine ligands (UniProt: Cys326, Cys332, Cys347 in precursor numbering).
        This is the Fe-S cluster designated N2, the terminal electron acceptor before
        ubiquinone in the Complex I Fe-S chain.
      action: ACCEPT
      reason: >-
        Core molecular function of NDUFS2. The [4Fe-4S] cluster (N2) is well-characterized
        structurally and is essential for electron transfer to ubiquinone. Confirmed
        by
        UniProt cofactor annotation and cryo-EM structures.
      supported_by:
        - reference_id: PMID:24089531
          supporting_text: >-
            The extrinsic arm contains binding sites for NADH and the primary electron
            acceptor
            FMN, and it provides a scaffold for seven iron-sulfur clusters that form
            an
            electron
            pathway linking FMN to the terminal electron acceptor, ubiquinone

# ============================================================
# PROTEIN BINDING ANNOTATIONS (IPI)
# ============================================================
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:15250827
    review:
      summary: >-
        IPI annotation for protein binding from a study on structural organization
        of
        human
        Complex I, examining interaction with prohibitin and role of ND4/ND5 subunits
        (PMID:15250827). NDUFS2 interacts with multiple other Complex I subunits as
        part of
        the holoenzyme, but 'protein binding' is uninformative.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic 'protein binding' does not convey useful information about NDUFS2
        function.
        The interaction is likely within the context of the Complex I holoenzyme.
        Subunit-subunit
        interactions within a multi-protein complex are expected and captured by the
        CC annotation
        to GO:0045271 (respiratory chain complex I).
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:19688755
    review:
      summary: >-
        IPI annotation from a mass spectrometry study analyzing protein complexes
        via
        blue
        native gel electrophoresis (PMID:19688755). The study identified NDUFS2 as
        part
        of
        Complex I. This is a high-throughput detection of known complex membership.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic 'protein binding' from a high-throughput study confirming known Complex
        I
        membership. Uninformative as a MF annotation.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:24344204
    review:
      summary: >-
        IPI from a study identifying TIMMDC1 as a Complex I assembly factor associated
        with
        the MCIA complex (PMID:24344204). The study shows NDUFS2 co-purifies with
        assembly
        intermediates. The protein binding annotation captures the interaction with
        assembly
        factors during Complex I biogenesis.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic 'protein binding' is uninformative. The relevant biology is Complex
        I assembly,
        already captured by the GO:0032981 annotation. NDUFS2 interacting with assembly
        factors
        is part of the normal assembly pathway, not a specific molecular function.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:27499296
    review:
      summary: >-
        IPI from a mitochondrial protein interaction mapping study (PMID:27499296).
        This is
        a high-throughput interaction screen identifying regulators of respiratory
        chain
        function.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic 'protein binding' from a high-throughput interaction mapping study.
        Uninformative
        as a molecular function annotation for NDUFS2.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:28514442
    review:
      summary: >-
        IPI from a large-scale human interactome study (PMID:28514442). This is a
        high-throughput
        study mapping protein communities and disease networks.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic 'protein binding' from a large-scale interactome study. Uninformative
        for
        understanding NDUFS2 molecular function.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:32807793
    review:
      summary: >-
        IPI from a study showing OSMR interacts with NDUFS1/NDUFS2 of Complex I and
        promotes
        mitochondrial respiration in glioma stem cells (PMID:32807793). The study
        demonstrates
        a mitochondrial OSMR that interacts with NDUFS2 to regulate oxidative phosphorylation.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        While the OSMR-NDUFS2 interaction is an interesting finding, 'protein binding'
        is
        uninformative. The functional consequence (regulation of Complex I activity)
        is more
        relevant than the generic binding annotation.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:33961781
    review:
      summary: >-
        IPI from a dual proteome-scale network study mapping cell-specific remodeling
        of the
        human interactome (PMID:33961781). High-throughput interaction data.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic 'protein binding' from a large-scale interactome study. Uninformative
        for
        NDUFS2 function.

# ============================================================
# IEA ANNOTATIONS (Ensembl Compara / combined)
# ============================================================
  - term:
      id: GO:0006120
      label: mitochondrial electron transport, NADH to ubiquinone
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        IEA from Ensembl Compara orthology transfer. Consistent with the IBA and multiple
        experimental annotations for this core process.
      action: ACCEPT
      reason: >-
        Correct, consistent with IBA and experimental evidence. Core process for NDUFS2.
  - term:
      id: GO:0019826
      label: oxygen sensor activity
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    review:
      summary: >-
        IEA for oxygen sensor activity. This annotation reflects findings from Dunham-Snary
        et al. (PMID:30922174) showing NDUFS2 is essential for acute oxygen sensing
        in
        pulmonary vasculature. Supported by the IMP annotation from the same reference.
      action: KEEP_AS_NON_CORE
      reason: >-
        Oxygen sensing is a tissue-specific function in pulmonary artery smooth muscle
        cells,
        not the core evolved function of NDUFS2. The primary role is as a Complex
        I
        catalytic
        subunit. The oxygen-sensing role appears to be a secondary consequence of
        the
        redox-sensitive [4Fe-4S] cluster and cysteine residues in NDUFS2, which are
        modified
        under hypoxic conditions. Keep as non-core.
      supported_by:
        - reference_id: PMID:30922174
          supporting_text: >-
            Ndufs2 is essential for oxygen-sensing and HPV
  - term:
      id: GO:0022008
      label: neurogenesis
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        IEA from Ensembl Compara orthology transfer for neurogenesis. Based on mouse
        model
        data (UniProt: By similarity) showing NDUFS2 is essential for neural stem
        and
        progenitor cell proliferation, differentiation and neuronal maturation. This
        is a
        downstream pleiotropic effect of Complex I deficiency, not a direct function.
      action: KEEP_AS_NON_CORE
      reason: >-
        Neurogenesis is a downstream pleiotropic effect of Complex I function, not
        a
        direct function of NDUFS2. Complex I deficiency impairs mitochondrial energy
        production needed for neural development. This is not a core evolved function
        of the gene product.
  - term:
      id: GO:0032981
      label: mitochondrial respiratory chain complex I assembly
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        IEA from Ensembl Compara for Complex I assembly. NDUFS2 is a core subunit
        of
        the
        Q-module that forms the initial nucleus of the peripheral arm junction with
        the
        membrane arm. Its methylation by NDUFAF7 at Arg-85 stabilizes the early 400
        kDa
        assembly intermediate (PMID:24089531). Mutations in NDUFS2 affect assembly
        (PMID:14749350).
      action: KEEP_AS_NON_CORE
      reason: >-
        NDUFS2 is essential for Complex I assembly as a structural core subunit, and
        its
        modification by NDUFAF7 is required for the assembly pathway. However, its
        role
        is
        primarily as a structural component that must be present for assembly to proceed,
        rather than having a specific assembly factor function. Assembly-related annotations
        for structural subunits are kept as non-core.
      supported_by:
        - reference_id: PMID:24089531
          supporting_text: >-
            This methylation step occurs early in the assembly of complex I and probably
            stabilizes a 400-kDa subcomplex that forms the initial nucleus of the
            peripheral
            arm and its juncture with the membrane arm
        - reference_id: PMID:14749350
          supporting_text: >-
            Our results show an important decrease in the levels of intact complex
            I in
            patients
            harboring mutations in nuclear-encoded complex I subunits, indicating
            that
            complex I
            assembly and/or stability is compromised
  - term:
      id: GO:0042063
      label: gliogenesis
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        IEA from Ensembl Compara for gliogenesis. Based on mouse model data (UniProt:
        By
        similarity) showing NDUFS2 is essential for glia-like neural stem and progenitor
        cell proliferation and oligodendrocyte maturation.
      action: KEEP_AS_NON_CORE
      reason: >-
        Gliogenesis is a downstream pleiotropic effect of Complex I function in neural
        tissue, not a direct function of NDUFS2. Energy metabolism is required for
        glial
        cell development, but this does not represent a specific molecular role of
        NDUFS2.
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    review:
      summary: >-
        IEA annotation for Complex I localization, consistent with the IBA and multiple
        experimental annotations.
      action: ACCEPT
      reason: >-
        Correct CC annotation, consistent with IBA and experimental evidence. Redundant
        but acceptable as an independent IEA.
  - term:
      id: GO:0061351
      label: neural precursor cell proliferation
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        IEA from Ensembl Compara for neural precursor cell proliferation. Based on
        mouse
        model data. Like neurogenesis and gliogenesis, this is a downstream pleiotropic
        effect of mitochondrial energy metabolism.
      action: KEEP_AS_NON_CORE
      reason: >-
        Neural precursor cell proliferation is a downstream pleiotropic effect of
        Complex
        I
        function, not a direct molecular function of NDUFS2. Keep as non-core.
  - term:
      id: GO:0071453
      label: cellular response to oxygen levels
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    review:
      summary: >-
        IEA for cellular response to oxygen levels. Consistent with the IMP annotation
        from PMID:30922174 demonstrating NDUFS2's role in oxygen sensing. The IEA
        likely
        derives from the experimental annotation.
      action: KEEP_AS_NON_CORE
      reason: >-
        Tissue-specific oxygen-sensing function in pulmonary vasculature, not a core
        evolved function. Keep as non-core, consistent with the oxygen sensor activity
        annotation.

# ============================================================
# EXPERIMENTAL ANNOTATIONS (IMP, IDA, NAS, TAS, HTP)
# ============================================================
  - term:
      id: GO:0003954
      label: NADH dehydrogenase activity
    evidence_type: IMP
    original_reference_id: PMID:14749350
    qualifier: contributes_to
    review:
      summary: >-
        IMP annotation with 'contributes_to' qualifier from Ugalde et al. (PMID:14749350).
        The study used blue native electrophoresis to show that NDUFS2 mutations decrease
        levels of intact Complex I and Complex I activity, demonstrating that NDUFS2
        contributes
        to NADH dehydrogenase activity. GO:0003954 (NADH dehydrogenase activity) is
        a broader
        parent of GO:0008137 (NADH dehydrogenase ubiquinone activity).
      action: ACCEPT
      reason: >-
        Valid annotation. The study demonstrates that mutations in NDUFS2 result in
        decreased
        Complex I activity. The 'contributes_to' qualifier is appropriate. GO:0003954
        is a
        parent term that captures the NADH dehydrogenase function; while GO:0008137
        would be
        more specific, both are valid. Duplicates with the GO:0008137 annotations
        at
        different
        specificity levels are acceptable.
      supported_by:
        - reference_id: PMID:14749350
          supporting_text: >-
            Our results show an important decrease in the levels of intact complex
            I in
            patients
            harboring mutations in nuclear-encoded complex I subunits, indicating
            that
            complex I
            assembly and/or stability is compromised
  - term:
      id: GO:0005743
      label: mitochondrial inner membrane
    evidence_type: IDA
    original_reference_id: PMID:28844695
    review:
      summary: >-
        IDA annotation from the cryo-EM megacomplex structure study (PMID:28844695).
        Guo et al.
        resolved the architecture of the human respiratory megacomplex I2III2IV2,
        directly
        visualizing NDUFS2 in the inner membrane Complex I structure.
      action: ACCEPT
      reason: >-
        Direct structural evidence from cryo-EM confirms NDUFS2 localization to the
        mitochondrial inner membrane as part of Complex I.
      supported_by:
        - reference_id: PMID:28844695
          supporting_text: >-
            The structure not only reveals the precise assignment of individual subunits
            of
            human CI and CIII, but also enables future in-depth analysis of the electron
            transport chain as a whole
  - term:
      id: GO:0009060
      label: aerobic respiration
    evidence_type: NAS
    original_reference_id: PMID:30030361
    review:
      summary: >-
        NAS annotation from a review on assembly of mammalian OXPHOS complexes (PMID:30030361).
        Complex I is the first enzyme of the mitochondrial respiratory chain, essential
        for
        aerobic respiration. NDUFS2 as a core subunit participates in this process.
      action: ACCEPT
      reason: >-
        Valid broader process annotation. Complex I is essential for aerobic respiration,
        and NDUFS2 is a core catalytic subunit. The NAS evidence from a comprehensive
        review
        is appropriate.
      supported_by:
        - reference_id: PMID:30030361
          supporting_text: >-
            The assembly of the five oxidative phosphorylation system (OXPHOS) complexes
            in
            the inner mitochondrial membrane is an intricate process
  - term:
      id: GO:0042776
      label: proton motive force-driven mitochondrial ATP synthesis
    evidence_type: NAS
    original_reference_id: PMID:30030361
    review:
      summary: >-
        NAS annotation from the same OXPHOS assembly review (PMID:30030361). Complex
        I
        contributes to proton motive force generation, which drives ATP synthesis.
        However,
        NDUFS2 does not directly participate in the proton pumping or ATP synthesis.
        This is
        an indirect downstream consequence of Complex I activity.
      action: KEEP_AS_NON_CORE
      reason: >-
        NDUFS2 contributes indirectly to proton motive force generation via its role
        in
        Complex I catalysis, but does not directly drive ATP synthesis. This is a
        downstream
        biological consequence rather than a core function of the gene product.
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: HTP
    original_reference_id: PMID:34800366
    review:
      summary: >-
        HTP annotation from a quantitative human mitochondrial proteome study (PMID:34800366).
        Mass spectrometry confirmed NDUFS2 as a high-confidence mitochondrial protein.
      action: ACCEPT
      reason: >-
        Correct CC annotation confirmed by high-throughput proteomics. The more specific
        annotations (inner membrane, Complex I) are also present.
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IMP
    original_reference_id: PMID:11112787
    review:
      summary: >-
        IMP annotation from Triepels et al. (PMID:11112787) showing that NDUFS2 mutations
        affect Complex I assembly patterns, demonstrated by monoclonal antibody analysis
        and sucrose gradient studies. The study examined patients with NDUFS2 mutations
        and
        showed altered Complex I subunit profiles.
      action: ACCEPT
      reason: >-
        Valid experimental evidence. The study demonstrates that NDUFS2 mutations
        disrupt
        Complex I integrity, confirming NDUFS2 as a component of respiratory chain
        Complex
        I.
      supported_by:
        - reference_id: PMID:11112787
          supporting_text: >-
            different mutations in the same gene are shown to give very similar subunit
            profiles
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IDA
    original_reference_id: PMID:12611891
    review:
      summary: >-
        IDA annotation from Murray et al. (PMID:12611891) who immunopurified human
        NADH
        dehydrogenase and identified 42 subunits including NDUFS2 by mass spectrometry.
      action: ACCEPT
      reason: >-
        Direct experimental identification of NDUFS2 as a subunit of immunopurified
        human
        Complex I by mass spectrometry.
      supported_by:
        - reference_id: PMID:12611891
          supporting_text: >-
            we can resolve and identify the human homologues of 42 polypeptides detected
            so far
            in the more extensively studied beef heart complex I
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IDA
    original_reference_id: PMID:17209039
    review:
      summary: >-
        IDA annotation from Vogel et al. (PMID:17209039). The study traced NDUFS3-GFP
        assembly
        intermediates and identified NDUFS2-containing subcomplexes during Complex
        I
        biogenesis,
        confirming NDUFS2 as a Complex I component.
      action: ACCEPT
      reason: >-
        Direct experimental evidence from assembly intermediate analysis confirming
        NDUFS2
        in Complex I subcomplexes.
      supported_by:
        - reference_id: PMID:17209039
          supporting_text: >-
            Upon induction, six distinct NDUFS3-GFP-containing subcomplexes gradually
            appeared
            on a blue native Western blot also observed in wild type HEK293 mitochondria
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IMP
    original_reference_id: PMID:24746669
    review:
      summary: >-
        IMP annotation from Wang et al. (PMID:24746669) showing cyclin B1/Cdk1 phosphorylates
        Complex I subunits including NDUFS2, affecting CI function. The study confirms
        NDUFS2
        as a Complex I subunit through functional phosphorylation studies.
      action: ACCEPT
      reason: >-
        NDUFS2 is confirmed as a Complex I subunit that is functionally regulated
        by
        phosphorylation during the cell cycle.
      supported_by:
        - reference_id: PMID:24746669
          supporting_text: >-
            Cyclin B1/Cdk1-mediated CI phosphorylation enhances CI activity, whereas
            deficiency
            of such phosphorylation in each of the relevant CI subunits results in
            impairment
            of CI function
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: NAS
    original_reference_id: PMID:9878551
    review:
      summary: >-
        NAS annotation from Loeffen et al. (PMID:9878551) who completed cDNA characterization
        of all nuclear-encoded Complex I subunits, establishing NDUFS2 as a Complex
        I component.
      action: ACCEPT
      reason: >-
        Early characterization study confirming NDUFS2 as a nuclear-encoded subunit
        of Complex I.
      supported_by:
        - reference_id: PMID:9878551
          supporting_text: >-
            Now all currently known 41 proteins of human NADH:ubiquinone oxidoreductase
            have
            been characterized and reported in literature
  - term:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    evidence_type: IMP
    original_reference_id: PMID:28031252
    review:
      summary: >-
        IMP annotation from Gerber et al. (PMID:28031252). The study identified compound
        heterozygous NDUFS2 mutations (Tyr53Cys; Tyr308Cys) causing LHON-like optic
        neuropathy. In the yeast Yarrowia lipolytica ortholog NUCM, mutations resulted
        in
        moderate reduction of NADH-ubiquinone oxidoreductase activity.
      action: ACCEPT
      reason: >-
        The study demonstrates that NDUFS2 mutations impair NADH dehydrogenase (ubiquinone)
        activity, confirming NDUFS2 contributes to this complex-level catalytic function.
        Note: the annotation lacks a 'contributes_to' qualifier which would be more
        appropriate for a complex subunit.
      supported_by:
        - reference_id: PMID:28031252
          supporting_text: >-
            In the yeast Y. lipolytica ortholog NUCM, the mutations resulted in absence
            of
            complex I and moderate reduction in nicotinamide adenine dinucleotide-ubiquinone
            oxidoreductase activity, respectively
  - term:
      id: GO:0006120
      label: mitochondrial electron transport, NADH to ubiquinone
    evidence_type: IMP
    original_reference_id: PMID:30922174
    review:
      summary: >-
        IMP annotation from Dunham-Snary et al. (PMID:30922174). The study showed
        that
        siRNA knockdown of Ndufs2 in pulmonary artery smooth muscle cells decreases
        Complex I
        activity and impairs mitochondrial electron transport.
      action: ACCEPT
      reason: >-
        Direct experimental evidence that NDUFS2 is required for mitochondrial electron
        transport from NADH to ubiquinone. Knockdown impairs Complex I-dependent respiration.
      supported_by:
        - reference_id: PMID:30922174
          supporting_text: >-
            In PASMC, siNdufs2 (cells/tissue treated with Ndufs2 siRNA) decreased
            normoxic
            H2O2, prevented hypoxic increases in [Ca2+]i, and
            mimicked aspects of chronic hypoxia, including decreasing Complex I activity,
            elevating the nicotinamide adenine dinucleotide (NADH/NAD+) ratio and
            decreasing expression of the O2-sensitive ion channel, Kv1.5
  - term:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    evidence_type: IMP
    original_reference_id: PMID:22036843
    qualifier: contributes_to
    review:
      summary: >-
        IMP with 'contributes_to' qualifier from Ngu et al. (PMID:22036843). The study
        showed that the NDUFS2 Asp446Asn mutation results in normal Complex I protein
        levels but strongly reduced catalytic activity, demonstrating a catalytic
        defect.
        The mutation resides near the coenzyme Q binding pocket.
      action: ACCEPT
      reason: >-
        Key experimental evidence demonstrating that NDUFS2 directly contributes to
        Complex I
        catalytic function. The Asp446Asn mutation specifically impairs catalysis
        while
        maintaining complex assembly, showing NDUFS2's direct role in the enzymatic
        reaction. The 'contributes_to' qualifier is correct.
      supported_by:
        - reference_id: PMID:22036843
          supporting_text: >-
            Complex I amounts in the patient carrying the Asp446Asn mutation were
            normal,
            while
            the complex I activity was strongly reduced, showing that the NDUFS2 mutation
            affects
            complex I enzymatic function ... We propose that the mutation interferes
            with
            the
            reduction of coenzyme Q or with the coupling of coenzyme Q reduction with
            the
            conformational changes involved in proton pumping of complex I
  - term:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    evidence_type: IMP
    original_reference_id: PMID:30922174
    qualifier: contributes_to
    review:
      summary: >-
        IMP with 'contributes_to' qualifier from Dunham-Snary et al. (PMID:30922174).
        siRNA knockdown of Ndufs2 decreased Complex I activity in pulmonary artery
        smooth
        muscle cells and caused functional inhibition of Complex I.
      action: ACCEPT
      reason: >-
        Valid experimental evidence. siRNA knockdown of NDUFS2 causes functional inhibition
        of Complex I, confirming that NDUFS2 contributes to NADH dehydrogenase (ubiquinone)
        activity. The 'contributes_to' qualifier is correct.
      supported_by:
        - reference_id: PMID:30922174
          supporting_text: >-
            Lung Ndufs2 cysteine residues became reduced during acute hypoxia and
            both
            hypoxia
            and reducing agents caused functional inhibition of Complex I
  - term:
      id: GO:0019826
      label: oxygen sensor activity
    evidence_type: IMP
    original_reference_id: PMID:30922174
    review:
      summary: >-
        IMP annotation for oxygen sensor activity from Dunham-Snary et al. (PMID:30922174).
        The study demonstrates that NDUFS2, as the rotenone-binding site of Complex
        I, is
        essential for oxygen sensing in pulmonary vasculature. Hypoxia reduces NDUFS2
        cysteine residues, causing functional inhibition of Complex I, decreasing
        H2O2
        production, and triggering calcium signaling for vasoconstriction.
      action: KEEP_AS_NON_CORE
      reason: >-
        The oxygen-sensing function is a tissue-specific (pulmonary artery smooth
        muscle
        cells)
        secondary consequence of NDUFS2's redox-sensitive properties. It is not the
        core
        evolved function of the gene product. The primary function is as a Complex
        I
        catalytic
        subunit. The oxygen-sensing mechanism exploits the redox chemistry of NDUFS2's
        cysteine residues and [4Fe-4S] cluster in a tissue-specific context. Notably,
        knockdown of other Complex I subunits (NDUFS1) or other proposed oxygen sensors
        (Rieske Fe-S center, COX4i2) had no effect on hypoxic calcium signaling, suggesting
        NDUFS2-specific involvement.
      supported_by:
        - reference_id: PMID:30922174
          supporting_text: >-
            Ndufs2 is essential for oxygen-sensing and HPV
        - reference_id: PMID:30922174
          supporting_text: >-
            Lung Ndufs2 cysteine residues became reduced during acute hypoxia and
            both
            hypoxia
            and reducing agents caused functional inhibition of Complex I
  - term:
      id: GO:0022008
      label: neurogenesis
    evidence_type: ISS
    original_reference_id: GO_REF:0000024
    review:
      summary: >-
        ISS annotation transferred from mouse ortholog by curator judgment. Based
        on
        mouse
        data showing NDUFS2 is essential for neural stem cell development (UniProt:
        By similarity).
      action: KEEP_AS_NON_CORE
      reason: >-
        Downstream pleiotropic effect of Complex I deficiency on neural development.
        Not a
        direct molecular function. Keep as non-core, consistent with the IEA annotation.
  - term:
      id: GO:0032981
      label: mitochondrial respiratory chain complex I assembly
    evidence_type: ISS
    original_reference_id: GO_REF:0000024
    review:
      summary: >-
        ISS annotation for Complex I assembly transferred from ortholog. NDUFS2 is
        a
        core
        subunit required for proper Complex I assembly, as demonstrated by multiple
        studies
        showing that NDUFS2 mutations impair Complex I integrity (PMID:14749350, PMID:11112787).
      action: KEEP_AS_NON_CORE
      reason: >-
        NDUFS2 is essential for Complex I assembly as a structural core subunit. However,
        the assembly role is secondary to its catalytic function. Keep as non-core.
      supported_by:
        - reference_id: PMID:14749350
          supporting_text: >-
            a specific decrease of fully-assembled complex III in patients with mutations
            in NDUFS2 and NDUFS4
  - term:
      id: GO:0042063
      label: gliogenesis
    evidence_type: ISS
    original_reference_id: GO_REF:0000024
    review:
      summary: >-
        ISS annotation transferred from mouse ortholog for gliogenesis. Downstream
        pleiotropic
        effect of Complex I function in neural tissue.
      action: KEEP_AS_NON_CORE
      reason: >-
        Downstream pleiotropic effect, not a direct function. Consistent with IEA
        annotation.
  - term:
      id: GO:0061351
      label: neural precursor cell proliferation
    evidence_type: ISS
    original_reference_id: GO_REF:0000024
    review:
      summary: >-
        ISS annotation transferred from mouse ortholog for neural precursor cell proliferation.
        Downstream pleiotropic effect of mitochondrial energy metabolism.
      action: KEEP_AS_NON_CORE
      reason: >-
        Downstream pleiotropic effect. Not a direct molecular function of NDUFS2.
        Consistent
        with the IEA annotation.
  - term:
      id: GO:0071453
      label: cellular response to oxygen levels
    evidence_type: IMP
    original_reference_id: PMID:30922174
    review:
      summary: >-
        IMP annotation from Dunham-Snary et al. (PMID:30922174). The study shows that
        NDUFS2 in pulmonary artery smooth muscle cells responds to hypoxia via reduction
        of
        cysteine residues, leading to Complex I inhibition and downstream signaling.
        This is
        the process-level annotation corresponding to the oxygen sensor activity MF
        annotation.
      action: KEEP_AS_NON_CORE
      reason: >-
        Tissue-specific oxygen-sensing function. The response to oxygen levels is
        a
        secondary
        consequence of NDUFS2's redox-sensitive properties in the pulmonary vasculature.
        Keep as non-core.
      supported_by:
        - reference_id: PMID:30922174
          supporting_text: >-
            Lung Ndufs2 cysteine residues became reduced during acute hypoxia and
            both
            hypoxia
            and reducing agents caused functional inhibition of Complex I
  - term:
      id: GO:0042775
      label: mitochondrial ATP synthesis coupled electron transport
    evidence_type: IMP
    original_reference_id: PMID:24746669
    review:
      summary: >-
        IMP annotation from Wang et al. (PMID:24746669). The study showed that cyclin
        B1/Cdk1
        phosphorylation of Complex I subunits including NDUFS2 enhances CI activity
        and increases
        ATP generation for G2/M cell cycle progression, demonstrating coupling between
        electron
        transport and ATP synthesis.
      action: ACCEPT
      reason: >-
        Valid process annotation. Complex I activity is coupled to ATP synthesis via
        proton
        motive force generation, and this study demonstrates that phosphorylation
        of
        NDUFS2
        and other CI subunits modulates this coupled process.
      supported_by:
        - reference_id: PMID:24746669
          supporting_text: >-
            Mitochondria-targeted cyclin B1/Cdk1 increases mitochondrial respiration
            with
            enhanced oxygen consumption and ATP generation, which provides cells with
            efficient
            bioenergy for G2/M transition
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:24089531
    review:
      summary: >-
        IPI annotation from Rhein et al. (PMID:24089531) showing NDUFS2 interacts
        with
        the
        methyltransferase NDUFAF7. NDUFAF7 symmetrically dimethylates Arg-85 in NDUFS2,
        a modification required for early Complex I assembly. This is a specific,
        functionally
        relevant interaction.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        While the NDUFS2-NDUFAF7 interaction is biologically important and well-characterized,
        'protein binding' is uninformative. The functional consequence (methylation
        of Arg-85
        for Complex I assembly) is more meaningful and is captured by assembly annotations.
      supported_by:
        - reference_id: PMID:24089531
          supporting_text: >-
            it has been demonstrated that it is a protein methylase that symmetrically
            dimethylates the omega-N(G),N(G') atoms of residue Arg-85 in the NDUFS2
            subunit of complex I

# ============================================================
# TAS ANNOTATIONS (Reactome)
# ============================================================
  - term:
      id: GO:0005759
      label: mitochondrial matrix
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-163217
    review:
      summary: >-
        TAS annotation from Reactome pathway for Complex I oxidation of NADH. NDUFS2
        is a
        peripheral membrane protein on the matrix side of the inner membrane. UniProt
        confirms
        subcellular location as mitochondrion inner membrane, matrix side.
      action: ACCEPT
      reason: >-
        Correct CC annotation. NDUFS2 is on the matrix-facing side of Complex I and
        participates in the matrix-arm catalytic reactions. The Reactome pathway correctly
        places NDUFS2 in the mitochondrial matrix context.
  - term:
      id: GO:0005759
      label: mitochondrial matrix
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6788523
    review:
      summary: >-
        TAS from Reactome pathway for NUBPL transfer of 4Fe-4S clusters to Complex
        I
        subunits.
        NDUFS2 receives its [4Fe-4S] cluster in the mitochondrial matrix during assembly.
      action: ACCEPT
      reason: >-
        Correct CC annotation. The [4Fe-4S] cluster insertion into NDUFS2 occurs in
        the
        mitochondrial matrix.
  - term:
      id: GO:0005759
      label: mitochondrial matrix
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6799178
    review:
      summary: >-
        TAS from Reactome Complex I assembly pathway. NDUFS2 is part of assembly intermediates
        that form in the mitochondrial matrix.
      action: ACCEPT
      reason: >-
        Correct CC annotation. Complex I assembly intermediates containing NDUFS2
        are
        in
        the mitochondrial matrix.
  - term:
      id: GO:0005759
      label: mitochondrial matrix
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6799179
    review:
      summary: >-
        TAS from Reactome Complex I assembly pathway for peripheral arm subunit binding.
      action: ACCEPT
      reason: >-
        Correct CC annotation, same rationale as other Reactome matrix annotations.
  - term:
      id: GO:0005759
      label: mitochondrial matrix
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6799191
    review:
      summary: >-
        TAS from Reactome for Intermediate 2 binding MT-ND1 subcomplex in the assembly
        pathway.
      action: ACCEPT
      reason: >-
        Correct CC annotation. Assembly intermediates form in the matrix.
  - term:
      id: GO:0005759
      label: mitochondrial matrix
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6799196
    review:
      summary: >-
        TAS from Reactome for dissociation of assembly factors from the 980kDa complex
        to
        yield mature Complex I.
      action: ACCEPT
      reason: >-
        Correct CC annotation. Final assembly steps occur at the matrix side of the
        inner membrane.
  - term:
      id: GO:0005759
      label: mitochondrial matrix
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6799197
    review:
      summary: >-
        TAS from Reactome for ND4/ND5 binding to the 550kDa assembly complex.
      action: ACCEPT
      reason: >-
        Correct CC annotation for NDUFS2 participating in matrix-localized assembly.
  - term:
      id: GO:0005759
      label: mitochondrial matrix
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6799202
    review:
      summary: >-
        TAS from Reactome for the 315kDa and 370kDa subcomplexes combining to form
        the
        550kDa complex during assembly.
      action: ACCEPT
      reason: >-
        Correct CC annotation. Assembly intermediates in the matrix.
  - term:
      id: GO:0005759
      label: mitochondrial matrix
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6799203
    review:
      summary: >-
        TAS from Reactome for IP subcomplex binding NDUFAF3, NDUFAF4, TIMMDC1 to form
        Intermediate 1. NDUFS2 is part of the IP (iron-sulfur protein) subcomplex.
      action: ACCEPT
      reason: >-
        Correct CC annotation. NDUFS2 is part of the IP subcomplex that assembles
        with
        factors in the matrix.
  - term:
      id: GO:0005759
      label: mitochondrial matrix
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6800868
    review:
      summary: >-
        TAS from Reactome for NDUF subunits binding to form the IP subcomplex. NDUFS2
        is
        a core component of this initial assembly step.
      action: ACCEPT
      reason: >-
        Correct CC annotation. The IP subcomplex containing NDUFS2 forms in the matrix.

# ============================================================
# ADDITIONAL EXPERIMENTAL ANNOTATIONS
# ============================================================
  - term:
      id: GO:0031625
      label: ubiquitin protein ligase binding
    evidence_type: IPI
    original_reference_id: PMID:19725078
    review:
      summary: >-
        IPI annotation from Davison et al. (PMID:19725078) showing NDUFS2 was identified
        as a potential interactant of Parkin (an E3 ubiquitin ligase) by tandem affinity
        purification and mass spectrometry. Parkin is involved in modulation of mitochondrial
        function and Parkinson's disease.
      action: KEEP_AS_NON_CORE
      reason: >-
        The interaction with Parkin suggests NDUFS2 may be a substrate or regulatory
        target
        of the ubiquitin-proteasome system in the context of mitochondrial quality
        control.
        This is more specific than generic 'protein binding' but represents a regulatory
        interaction rather than a core function. Keep as non-core.
      supported_by:
        - reference_id: PMID:19725078
          supporting_text: >-
            Tandem affinity purification/MS revealed 14 potential interactants of
            Parkin;
            CKB, DBT, HSPD1, HSPA9, LRPPRC, NDUFS2, PRDX6, SLC25A5, TPI1, UCHL1, UQCRC1,
            VCL, YWHAZ, YWHAE
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:20406883
    review:
      summary: >-
        IPI from Carilla-Latorre et al. (PMID:20406883) showing that both Dictyostelium
        and
        human MidA (NDUFAF7) interact with the NDUFS2 subunit via yeast two-hybrid
        screening
        and pull-down experiments.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic 'protein binding' is uninformative. The relevant interaction is with
        NDUFAF7
        (MidA) methyltransferase for Complex I assembly. This functional role is captured
        by assembly annotations.
      supported_by:
        - reference_id: PMID:20406883
          supporting_text: >-
            Using yeast two-hybrid screening and pull-down experiments, we showed
            that
            both
            proteins interact with the mitochondrial complex I subunit NDUFS2
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:19463981
    review:
      summary: >-
        IPI from Saada et al. (PMID:19463981) showing NDUFAF3 interacts with Complex
        I
        subunits during assembly. NDUFS2 co-purifies with the assembly factor complex.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic 'protein binding' is uninformative. The NDUFAF3 interaction is in
        the
        context of Complex I assembly, captured by the assembly annotations.
      supported_by:
        - reference_id: PMID:19463981
          supporting_text: >-
            NDUFAF3 is a genuine mitochondrial complex I assembly protein that interacts
            with complex I subunits
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: IDA
    original_reference_id: PMID:9585441
    review:
      summary: >-
        IDA annotation from Procaccio et al. (PMID:9585441) who mapped the NDUFS2
        gene
        to
        chromosome 1q23 and performed immunodetection of the mature protein in mitochondria.
      action: ACCEPT
      reason: >-
        Direct experimental evidence of NDUFS2 protein in mitochondria by immunodetection.
        An early but valid demonstration of mitochondrial localization.
      supported_by:
        - reference_id: PMID:9585441
          supporting_text: >-
            Mapping to 1q23 of the human gene (NDUFS2) encoding the 49-kDa subunit
            of
            the
            mitochondrial respiratory Complex I and immunodetection of the mature
            protein
            in mitochondria
  - term:
      id: GO:0006120
      label: mitochondrial electron transport, NADH to ubiquinone
    evidence_type: NAS
    original_reference_id: PMID:9878551
    review:
      summary: >-
        NAS from Loeffen et al. (PMID:9878551) who completed cDNA characterization
        of
        nuclear-encoded Complex I subunits. The study establishes NDUFS2 as a subunit
        of
        the enzyme whose main function is electron transport from NADH to ubiquinone.
      action: ACCEPT
      reason: >-
        Valid NAS annotation from an authoritative early characterization study.
      supported_by:
        - reference_id: PMID:9878551
          supporting_text: >-
            NADH:ubiquinone oxidoreductase (complex I) is an extremely complicated
            multiprotein
            complex located in the inner mitochondrial membrane. Its main function
            is
            the transport
            of electrons from NADH to ubiquinone
  - term:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    evidence_type: NAS
    original_reference_id: PMID:9878551
    review:
      summary: >-
        NAS from the same Loeffen et al. study (PMID:9878551) characterizing Complex
        I cDNAs.
      action: ACCEPT
      reason: >-
        Valid NAS annotation from an authoritative characterization study. NDUFS2
        is
        a core
        catalytic subunit of the NADH:ubiquinone oxidoreductase.
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: NAS
    original_reference_id: PMID:9647766
    review:
      summary: >-
        NAS from Loeffen et al. (PMID:9647766) who completed cDNA cloning of the iron-sulfur
        protein subunits of Complex I including NDUFS2.
      action: ACCEPT
      reason: >-
        Valid NAS annotation. The study establishes NDUFS2 as a mitochondrial protein.
      supported_by:
        - reference_id: PMID:9647766
          supporting_text: >-
            NADH:ubiquinone oxidoreductase (complex I) of the mitochondrial respiratory
            chain
            can be fragmented in a flavoprotein (FP), iron-sulfur protein (IP), and
            hydrophobic
            protein (HP) subfraction
  - term:
      id: GO:0006120
      label: mitochondrial electron transport, NADH to ubiquinone
    evidence_type: NAS
    original_reference_id: PMID:9647766
    review:
      summary: >-
        NAS from Loeffen et al. (PMID:9647766). The study characterizes NDUFS2 as
        part
        of
        the iron-sulfur protein fraction of Complex I involved in electron transport.
      action: ACCEPT
      reason: >-
        Valid NAS annotation from the original cDNA characterization study.
  - term:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    evidence_type: NAS
    original_reference_id: PMID:9647766
    review:
      summary: >-
        NAS from Loeffen et al. (PMID:9647766) characterizing NDUFS2 as part of the
        NADH:ubiquinone oxidoreductase complex.
      action: ACCEPT
      reason: >-
        Valid NAS annotation from the original characterization study.
  - term:
      id: GO:0009055
      label: electron transfer activity
    evidence_type: NAS
    original_reference_id: PMID:9647766
    review:
      summary: >-
        NAS from Loeffen et al. (PMID:9647766). NDUFS2 is in the iron-sulfur protein
        (IP)
        fraction and contains a [4Fe-4S] cluster that participates in the electron
        relay
        chain within Complex I. The IP subfraction is significant because it contains
        important prosthetic groups highly conserved among species.
      action: ACCEPT
      reason: >-
        Valid MF annotation. NDUFS2 contains a [4Fe-4S] cluster (designated N2) that
        is the
        terminal electron acceptor in the Fe-S chain before ubiquinone reduction.
        Electron
        transfer activity is a core molecular function of NDUFS2.
      supported_by:
        - reference_id: PMID:9647766
          supporting_text: >-
            The IP subfraction is hypothesized to be significant, since it contains
            important
            prosthetic groups highly conserved among species

# ============================================================
# NEW ANNOTATIONS (suggested additions)
# ============================================================
  - term:
      id: GO:0048039
      label: ubiquinone binding
    evidence_type: IDA
    original_reference_id: PMID:28844695
    review:
      summary: >-
        NDUFS2 directly forms the ubiquinone-binding channel with its conserved His59/Tyr108
        residue pair contacting the quinone headgroup, as revealed by cryo-EM structures
        (PMID:28844695) and confirmed by molecular dynamics simulations and inhibitor
        binding
        studies. The Asp446Asn mutation near the Q-binding pocket specifically impairs
        catalysis without affecting complex assembly (PMID:22036843). This is a key
        molecular
        function not explicitly captured at the correct specificity in the existing
        annotation
        set (only the broader GO:0048038 quinone binding is present as IEA).
      action: NEW
      reason: >-
        Ubiquinone binding is a core molecular function of NDUFS2, directly supported
        by
        structural evidence showing NDUFS2 His59/Tyr108 form the Q-binding site and
        by
        mutational studies showing catalytic defects from Q-pocket mutations. This
        annotation
        adds specificity beyond the existing IEA for GO:0048038 (quinone binding).
      supported_by:
        - reference_id: PMID:22036843
          supporting_text: >-
            A 3-D model of the catalytic core of complex I showed that the mutated
            amino
            acid residue resides near the coenzyme Q binding pocket
        - reference_id: file:human/NDUFS2/NDUFS2-deep-research-falcon.md
          supporting_text: >-
            NDUFS2 lines the amphipathic Q-channel and contributes the conserved His/Tyr
            ligand pair (His59, Tyr108) that interacts with the quinone headgroup
            and
            small-molecule Q-site ligands
core_functions:
  - molecular_function:
      id: GO:0048039
      label: ubiquinone binding
    contributes_to_molecular_function:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    directly_involved_in:
      - id: GO:0006120
        label: mitochondrial electron transport, NADH to ubiquinone
    locations:
      - id: GO:0005759
        label: mitochondrial matrix
    in_complex:
      id: GO:0045271
      label: respiratory chain complex I
    description: >-
      NDUFS2 is the 49 kDa core catalytic subunit of mitochondrial Complex I (NADH:ubiquinone
      oxidoreductase, EC 7.1.1.2), located in the Q-module of the peripheral (matrix-facing)
      arm. It directly forms the ubiquinone-binding channel with the conserved His59/Tyr108
      residue pair that contacts and orients the ubiquinone headgroup during reduction.
      NDUFS2
      binds one [4Fe-4S] cluster (designated N2), the terminal electron acceptor in
      the Fe-S
      relay chain before ubiquinone. NDUFS2 enables ubiquinone binding (GO:0048039)
      and electron
      transfer activity via its N2 cluster, and contributes to the overall NADH dehydrogenase
      (ubiquinone) activity (GO:0008137) of the 45-subunit Complex I holoenzyme. The
      Asp446Asn
      mutation near the coenzyme Q binding pocket specifically impairs catalytic activity
      without
      affecting complex assembly, demonstrating NDUFS2's direct role in the enzymatic
      reaction.
      NDUFS2 is dimethylated at Arg-85 by the assembly factor NDUFAF7, a modification
      required
      for stabilization of early assembly intermediates. Pathogenic mutations cause
      mitochondrial
      Complex I deficiency (MC1DN6, Leigh syndrome) and Leber-like hereditary optic
      neuropathy
      (LHONAR2).
    supported_by:
      - reference_id: PMID:22036843
        supporting_text: >-
          Complex I amounts in the patient carrying the Asp446Asn mutation were normal,
          while
          the complex I activity was strongly reduced, showing that the NDUFS2 mutation
          affects
          complex I enzymatic function
      - reference_id: PMID:30922174
        supporting_text: >-
          siNdufs2 ... mimicked aspects of chronic hypoxia, including decreasing Complex
          I
          activity, elevating the nicotinamide adenine dinucleotide (NADH/NAD+) ratio
      - reference_id: PMID:28844695
        supporting_text: >-
          The structure not only reveals the precise assignment of individual subunits
          of
          human CI and CIII, but also enables future in-depth analysis of the electron
          transport chain as a whole
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:0000043
    title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
    findings: []
  - id: GO_REF:0000107
    title: Automatic transfer of experimentally verified manual GO annotation data
      to orthologs using Ensembl Compara
    findings: []
  - id: GO_REF:0000108
    title: Automatic assignment of GO terms using logical inference, based on on inter-ontology
      links
    findings: []
  - id: GO_REF:0000120
    title: Combined Automated Annotation using Multiple IEA Methods
    findings: []
  - id: PMID:11112787
    title: Human complex I defects can be resolved by monoclonal antibody analysis
      into distinct subunit assembly patterns.
    findings: []
  - id: PMID:12611891
    title: The subunit composition of the human NADH dehydrogenase obtained by rapid
      one-step immunopurification.
    findings: []
  - id: PMID:14749350
    title: Differences in assembly or stability of complex I and other mitochondrial
      OXPHOS complexes in inherited complex I deficiency.
    findings: []
  - id: PMID:15250827
    title: 'Structural organization of mitochondrial human complex I: role of the
      ND4 and ND5 mitochondria-encoded subunits and interaction with prohibitin.'
    findings: []
  - id: PMID:17209039
    title: Identification of mitochondrial complex I assembly intermediates by tracing
      tagged NDUFS3 demonstrates the entry point of mitochondrial subunits.
    findings: []
  - id: PMID:19463981
    title: Mutations in NDUFAF3 (C3ORF60), encoding an NDUFAF4 (C6ORF66)-interacting
      complex I assembly protein, cause fatal neonatal mitochondrial disease.
    findings: []
  - id: PMID:19688755
    title: LC-MS/MS as an alternative for SDS-PAGE in blue native analysis of protein
      complexes.
    findings: []
  - id: PMID:19725078
    title: Proteomic analysis of increased Parkin expression and its interactants
      provides evidence for a role in modulation of mitochondrial function.
    findings: []
  - id: PMID:20406883
    title: MidA is a putative methyltransferase that is required for mitochondrial
      complex I function.
    findings: []
  - id: PMID:22036843
    title: A catalytic defect in mitochondrial respiratory chain complex I due to
      a mutation in NDUFS2 in a patient with Leigh syndrome.
    findings: []
  - id: PMID:24089531
    title: NDUFAF7 methylates arginine 85 in the NDUFS2 subunit of human complex I.
    findings: []
  - id: PMID:24344204
    title: TIMMDC1/C3orf1 functions as a membrane-embedded mitochondrial complex I
      assembly factor through association with the MCIA complex.
    findings: []
  - id: PMID:24746669
    title: Cyclin B1/Cdk1 coordinates mitochondrial respiration for cell-cycle G2/M
      progression.
    findings: []
  - id: PMID:27499296
    title: Mitochondrial Protein Interaction Mapping Identifies Regulators of Respiratory
      Chain Function.
    findings: []
  - id: PMID:28031252
    title: Compound heterozygosity for severe and hypomorphic NDUFS2 mutations cause
      non-syndromic LHON-like optic neuropathy.
    findings: []
  - id: PMID:28514442
    title: Architecture of the human interactome defines protein communities and disease
      networks.
    findings: []
  - id: PMID:28844695
    title: Architecture of Human Mitochondrial Respiratory Megacomplex I(2)III(2)IV(2).
    findings: []
  - id: PMID:30030361
    title: Assembly of mammalian oxidative phosphorylation complexes I-V and supercomplexes.
    findings: []
  - id: PMID:30922174
    title: Ndufs2, a Core Subunit of Mitochondrial Complex I, Is Essential for Acute
      Oxygen-Sensing and Hypoxic Pulmonary Vasoconstriction.
    findings: []
  - id: PMID:32807793
    title: OSMR controls glioma stem cell respiration and confers resistance of glioblastoma
      to ionizing radiation.
    findings: []
  - id: PMID:33961781
    title: Dual proteome-scale networks reveal cell-specific remodeling of the human
      interactome.
    findings: []
  - id: PMID:34800366
    title: Quantitative high-confidence human mitochondrial proteome and its dynamics
      in cellular context.
    findings: []
  - id: PMID:9585441
    title: Mapping to 1q23 of the human gene (NDUFS2) encoding the 49-kDa subunit
      of the mitochondrial respiratory Complex I and immunodetection of the mature
      protein in mitochondria.
    findings: []
  - id: PMID:9647766
    title: 'cDNA sequence and chromosomal localization of the remaining three human
      nuclear encoded iron sulphur protein (IP) subunits of complex I: the human IP
      fraction is completed.'
    findings: []
  - id: PMID:9878551
    title: 'cDNA of eight nuclear encoded subunits of NADH:ubiquinone oxidoreductase:
      human complex I cDNA characterization completed.'
    findings: []
  - id: Reactome:R-HSA-163217
    title: Complex I oxidises NADH to NAD+, reduces CoQ to CoQH2
    findings: []
  - id: Reactome:R-HSA-6788523
    title: NUBPL transfers 4Fe-4S to Complex I subunits
    findings: []
  - id: Reactome:R-HSA-6799178
    title: Intermediate 1 binds HP subcomplex to form Intermediate 2
    findings: []
  - id: Reactome:R-HSA-6799179
    title: Peripheral arm subunits bind the 815kDa complex to form a 980kDa complex
    findings: []
  - id: Reactome:R-HSA-6799191
    title: Intermediate 2 binds MT-ND1:NDUFAF5:NDUFAF6 to form a 315kDa subcomplex
    findings: []
  - id: Reactome:R-HSA-6799196
    title: The MCIA complex, NDUFAF2-7 all dissociate from the 980kDa complex, resulting
      in Complex I
    findings: []
  - id: Reactome:R-HSA-6799197
    title: ND4, ND5 bind the 550kDa complex to form the 815kDa complex
    findings: []
  - id: Reactome:R-HSA-6799202
    title: The 315kDa subcomplex binds the 370kDa subcomplex to form the 550kDa complex
    findings: []
  - id: Reactome:R-HSA-6799203
    title: IP subcomplex binds NDUFAF3, NDUFAF4, TIMMDC1 to form Intermediate 1
    findings: []
  - id: Reactome:R-HSA-6800868
    title: NDUF subunits bind to form the IP subcomplex
    findings: []