SCO2

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0033617 mitochondrial respiratory chain complex IV assembly	IBA GO_REF:0000033	ACCEPT	Summary: SCO2 is a well-established assembly factor for mitochondrial Complex IV (cytochrome c oxidase). The IBA phylogenetic inference is strongly supported by the conserved function of SCO proteins from yeast to human. SCO2 participates in the CuA-site assembly of COX2, a core step of CIV biogenesis (PMID:15229189, PMID:19336478, PMID:25959673). The founding disease paper (PMID:10545952) identified SCO2 as a COX assembly gene through mutations causing COX deficiency. Reason: Mitochondrial respiratory chain complex IV assembly is the core biological process of SCO2. This IBA annotation is well-supported by extensive experimental evidence from multiple organisms and is at the correct level of specificity. SCO2 functions specifically in the CuA-site assembly step of COX2 maturation within the broader CIV assembly pathway. Supporting Evidence: PMID:10545952 we have identified mutations in the human homologue, SCO2, in three unrelated infants with a newly recognized fatal cardioencephalomyopathy and COX deficiency PMID:15229189 We propose a model in which COX17 delivers copper to SCO2, which in turn transfers it directly to the CuA site at an early stage of COX assembly in a reaction that is facilitated by SCO1. PMID:19336478 Based on these data we present a model in which each SCO protein fulfills distinct, stage-specific functions during CO II synthesis and CuA site maturation.
GO:0005507 copper ion binding	IEA GO_REF:0000002	ACCEPT	Summary: SCO2 binds copper ions via its conserved CXXXC motif (Cys133 and Cys137) and an additional His224 ligand, as demonstrated by the NMR structure (PMID:17850752, PDB:2RLI). The InterPro-based IEA annotation is correct and well-supported by structural evidence. Copper ion binding is a core molecular function of SCO2, essential for its role as a copper chaperone in CuA-site assembly. Reason: Copper ion binding is a core molecular function of SCO2. The structural data from PMID:17850752 directly demonstrates copper coordination by the CXXXC motif (C133 and C137) and H224. The IEA annotation from InterPro is consistent with experimental evidence and is at the correct level of specificity. Supporting Evidence: PMID:15229189 Human SCO1 and SCO2 are paralogous genes that code for metallochaperone proteins with essential, but poorly understood, roles in copper delivery to cytochrome c oxidase (COX). file:human/SCO2/SCO2-deep-research-falcon.md SCO2 is a member of the conserved SCO1/2 family with a thioredoxin-like fold and the hallmark Cys-x-x-x-Cys motif central to redox and copper-binding chemistry in CuA assembly
GO:0005743 mitochondrial inner membrane	IEA GO_REF:0000120	ACCEPT	Summary: SCO2 is an integral protein of the mitochondrial inner membrane with a single transmembrane helix (residues 61-78) and its functional thioredoxin domain exposed to the intermembrane space (PMID:15229189). The IEA annotation from combined automated methods is correct and supported by direct experimental evidence (IDA from PMID:15229189). Reason: Mitochondrial inner membrane localization is well-established for SCO2 through both topology studies and fractionation experiments. This IEA is consistent with the experimentally verified IDA annotation from PMID:15229189. Supporting Evidence: PMID:15229189 To investigate the molecular function of the SCO proteins, we characterized the mitochondrial copper delivery pathway in SCO1 and SCO2 patient backgrounds.
GO:0006878 intracellular copper ion homeostasis	IEA GO_REF:0000002	KEEP AS NON CORE	Summary: SCO2 has a primary role as a copper chaperone delivering copper to the CuA site of COX2 during Complex IV assembly. PMID:17189203 (Leary et al. 2007) demonstrated that SCO proteins have regulatory roles in the maintenance of cellular copper homeostasis, providing some support for this annotation. However, SCO2's primary function is copper delivery to COX2 for CIV assembly, not broad cellular copper homeostasis. The copper homeostasis role is secondary and context-dependent. Reason: While SCO2 does participate in copper handling, its primary role is copper delivery to COX2 in the context of CIV assembly, not broad intracellular copper homeostasis. The copper homeostasis function described in PMID:17189203 represents a regulatory or secondary effect rather than the core evolved function of SCO2. Keeping as non-core rather than removing because there is published evidence for a regulatory role in copper homeostasis. Supporting Evidence: PMID:15229189 Our results demonstrate that the human SCO proteins have non-overlapping, cooperative functions in mitochondrial copper delivery.
GO:0008535 respiratory chain complex IV assembly	IEA GO_REF:0000002	ACCEPT	Summary: GO:0008535 (respiratory chain complex IV assembly) is the broader parent term of GO:0033617 (mitochondrial respiratory chain complex IV assembly). Since SCO2 specifically functions in mitochondrial CIV assembly, the more specific child term GO:0033617 is more appropriate. However, the broader term is not incorrect and is acceptable as an IEA annotation. Reason: This is the parent term of GO:0033617 which is already annotated with stronger evidence. While slightly less specific than the mitochondrial-specific child term, it is not incorrect for an IEA annotation and is subsumed by the more specific annotation. Supporting Evidence: PMID:10545952 Fatal infantile cardioencephalomyopathy with COX deficiency and mutations in SCO2, a COX assembly gene.
GO:0016531 copper chaperone activity	IEA GO_REF:0000002	ACCEPT	Summary: Copper chaperone activity (directly binding to and delivering copper ions to a target protein) is a core molecular function of SCO2. SCO2 delivers copper to the CuA site of COX2 in cooperation with SCO1. Multiple studies confirm this role (PMID:15229189, PMID:19336478, PMID:25959673). The InterPro-based IEA annotation correctly captures this core function. Reason: Copper chaperone activity is the primary molecular function of SCO2. It directly binds copper and delivers it to the CuA site of COX2. This is strongly supported by structural (PMID:17850752), genetic (PMID:10545952, PMID:15229189), and biochemical (PMID:19336478, PMID:25959673) evidence. Supporting Evidence: PMID:15229189 Human SCO1 and SCO2 are paralogous genes that code for metallochaperone proteins with essential, but poorly understood, roles in copper delivery to cytochrome c oxidase (COX). PMID:25959673 Our analyses define COA6 as a constituent of the mitochondrial copper relay system, linking defects in COX2 metallation to cardiac cytochrome c oxidase deficiency.
GO:0017004 cytochrome complex assembly	IEA GO_REF:0000043	ACCEPT	Summary: GO:0017004 (cytochrome complex assembly) is a broader parent of GO:0033617 (mitochondrial respiratory chain complex IV assembly). SCO2 is specifically involved in cytochrome c oxidase (Complex IV) assembly, not general cytochrome complex assembly. The UniProtKB-KW keyword mapping generated this broader term. While not incorrect, the more specific term GO:0033617 is preferred. Reason: This is a correct but overly broad IEA annotation. SCO2 does participate in cytochrome complex assembly (specifically cytochrome c oxidase), so the term is not wrong. It is subsumed by the more specific annotation GO:0033617. Acceptable as an IEA annotation. Supporting Evidence: PMID:10545952 Fatal infantile cardioencephalomyopathy with COX deficiency and mutations in SCO2, a COX assembly gene.
GO:0033617 mitochondrial respiratory chain complex IV assembly	IEA GO_REF:0000117	ACCEPT	Summary: This ARBA machine-learning IEA annotation for mitochondrial respiratory chain complex IV assembly is correct and consistent with the IBA and experimental annotations for the same term. It is a duplicate in terms of the GO term but from a different evidence source. Reason: Correct IEA annotation consistent with the core function of SCO2 in CIV assembly. The ARBA model correctly identified this function. Supporting Evidence: PMID:10545952 we have identified mutations in the human homologue, SCO2, in three unrelated infants with a newly recognized fatal cardioencephalomyopathy and COX deficiency
GO:0046872 metal ion binding	IEA GO_REF:0000043	ACCEPT	Summary: GO:0046872 (metal ion binding) is a very broad parent term. SCO2 specifically binds copper ions (GO:0005507), which is already annotated. The keyword-mapped IEA is not incorrect but is too general to be informative. Reason: While this is a very generic term, it is not incorrect for an IEA annotation derived from keyword mapping. It is subsumed by the more specific copper ion binding annotation (GO:0005507). Acceptable to keep as IEA. Supporting Evidence: PMID:15229189 Human SCO1 and SCO2 are paralogous genes that code for metallochaperone proteins with essential, but poorly understood, roles in copper delivery to cytochrome c oxidase (COX).
GO:0005515 protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	MARK AS OVER ANNOTATED	Summary: This IPI annotation is based on a high-throughput binary interactome screen (HI-Union, PMID:32296183) that detected an interaction between SCO2 and CIDEB (Q9UHD4). CIDEB is a cell death-inducing DFFA-like effector involved in lipid metabolism and apoptosis. This interaction lacks biological plausibility in the context of SCO2's known function as a mitochondrial copper chaperone for CIV assembly. The interaction with CIDEB is likely a false positive from the high-throughput screen. Reason: Generic protein binding annotation based on a high-throughput binary interactome screen. The detected interactor (CIDEB) has no known role in mitochondrial copper delivery or CIV assembly. SCO2 has well-characterized, functionally relevant interactions with COX20, SCO1, COA6, COX16, and TMEM177 that are already captured by other IPI annotations. This annotation does not provide informative functional information. Supporting Evidence: PMID:32296183 A reference map of the human binary protein interactome.
GO:0005739 mitochondrion	IEA GO_REF:0000107	ACCEPT	Summary: SCO2 is unambiguously a mitochondrial protein. This IEA annotation via Ensembl Compara ortholog transfer is correct and consistent with the IDA and HTP annotations for the same term. UniProt annotates SCO2 with a mitochondrial transit peptide (residues 1-41). Reason: Correct IEA annotation. Mitochondrial localization is universally supported. While the more specific mitochondrial inner membrane annotation (GO:0005743) is also present, having the broader mitochondrion annotation is acceptable. Supporting Evidence: PMID:15229189 To investigate the molecular function of the SCO proteins, we characterized the mitochondrial copper delivery pathway in SCO1 and SCO2 patient backgrounds.
GO:0005739 mitochondrion	IDA GO_REF:0000052	ACCEPT	Summary: This IDA annotation from Human Protein Atlas immunofluorescence data (HPA) confirms mitochondrial localization of SCO2 by direct assay. This is consistent with SCO2's known function as a mitochondrial inner membrane protein. Reason: Direct experimental evidence (immunofluorescence) for mitochondrial localization, consistent with all other evidence sources. The broader mitochondrion term is acceptable from IDA/immunofluorescence which may not resolve to the inner membrane. Supporting Evidence: PMID:15229189 To investigate the molecular function of the SCO proteins, we characterized the mitochondrial copper delivery pathway in SCO1 and SCO2 patient backgrounds.
GO:0005739 mitochondrion	HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an...	ACCEPT	Summary: This HTP annotation comes from the quantitative high-confidence human mitochondrial proteome study (Morgenstern et al. 2021). SCO2 was identified as a bona fide mitochondrial protein by mass spectrometry-based proteomics. This is consistent with its known function and localization. Reason: High-throughput proteomics confirmation of mitochondrial localization. Consistent with all other localization evidence for SCO2. Supporting Evidence: PMID:34800366 Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context.
GO:0005743 mitochondrial inner membrane	TAS Reactome:R-HSA-5632766	ACCEPT	Summary: This TAS annotation derives from the Reactome pathway entry for TP53-stimulated SCO2 transcription. The Reactome entry describes SCO2 as a "copper-binding assembly protein" that localizes to the mitochondrial inner membrane. This is consistent with experimental evidence (PMID:15229189). Reason: Correct localization annotation supported by Reactome curation. SCO2 is experimentally verified as a mitochondrial inner membrane protein with a single transmembrane helix. Supporting Evidence: Reactome:R-HSA-5632766 SCO2, synthesis of cytochrome c oxidase 2, is a copper-binding assembly protein for the mitochondrial COX (cytochrome C oxidase) complex
GO:0005743 mitochondrial inner membrane	TAS Reactome:R-HSA-9865449	ACCEPT	Summary: This TAS annotation derives from the Reactome pathway entry describing the metallochaperone complex that inserts Cu2+ into MT-CO1. The Reactome entry describes SCO2 as part of a nine-subunit metallochaperone complex on the inner mitochondrial membrane. Note that SCO2's primary role is copper delivery to COX2 (CuA site), not COX1 (CuB site). The Reactome entry groups SCO2 into a broader metallochaperone complex that may be somewhat oversimplified. Reason: The localization to mitochondrial inner membrane is correct regardless of whether the broader metallochaperone complex model in Reactome is precisely accurate. SCO2 is an inner membrane protein. Supporting Evidence: Reactome:R-HSA-9865449 A metallochaperone complex consisting of nine subunits (COA3, COA5, COX10, dimeric COX11, COX15, COX16, COX19, SCO1, SCO2)
GO:0005743 mitochondrial inner membrane	TAS Reactome:R-HSA-9865579	ACCEPT	Summary: This TAS annotation derives from the Reactome pathway entry describing the association of MT-CO1 and MT-CO2 complexes with heme moiety installation. The Reactome entry describes SCO2 as part of the COX2-specific copper chaperone module (with COA6 and SCO1). The localization to the mitochondrial inner membrane is correct. Reason: Correct localization annotation. SCO2 functions at the mitochondrial inner membrane during CIV assembly. Supporting Evidence: Reactome:R-HSA-9865579 A dynamic metallochaperone complex involving the heme A biosynthetic enzymes COX10 and COX15, together with COX2-specific copper chaperones COA6, SCO1, and SCO2
GO:0005743 mitochondrial inner membrane	TAS Reactome:R-HSA-9865630	ACCEPT	Summary: This TAS annotation derives from the Reactome pathway entry describing copper insertion into MT-CO2 (the CuA site). This is the most directly relevant Reactome entry for SCO2's function, as it describes the specific step SCO2 participates in. The localization to the mitochondrial inner membrane is correct. Reason: Correct localization annotation from the most functionally relevant Reactome pathway entry for SCO2. The CuA insertion into MT-CO2 is the core function of SCO2. Supporting Evidence: Reactome:R-HSA-9865630 A metallochaperone complex consisting of nine subunits (COA3, COA5, COX10, dimeric COX11, COX15, COX16, COX19, SCO1, SCO2) carries two copper cations ...to the pre-assembled MT-CO2 subunit. These copper ions are frequently called CuA
GO:0033617 mitochondrial respiratory chain complex IV assembly	TAS PMID:10545952 Fatal infantile cardioencephalomyopathy with COX deficiency ...	ACCEPT	Summary: This TAS annotation from the founding SCO2 disease paper (Papadopoulou et al. 1999) is well-supported. The paper identified SCO2 as a COX assembly gene through the discovery that mutations cause fatal infantile cardioencephalomyopathy with COX deficiency. Reason: Core biological process annotation supported by the founding publication for SCO2 disease. The paper established that SCO2 mutations cause COX deficiency, demonstrating its role in CIV assembly. Supporting Evidence: PMID:10545952 we have identified mutations in the human homologue, SCO2, in three unrelated infants with a newly recognized fatal cardioencephalomyopathy and COX deficiency...Immunohistochemical studies implied that the enzymatic deficiency, which was most severe in cardiac and skeletal muscle, was due to the loss of mtDNA-encoded COX subunits.
GO:0005515 protein binding	IPI PMID:29381136 COX16 promotes COX2 metallation and assembly during respirat...	MARK AS OVER ANNOTATED	Summary: This IPI annotation records the interaction between SCO2 and COX16 (Q9P0S2) demonstrated in PMID:29381136. COX16 was shown to interact with newly synthesized COX2 and its copper center-forming metallochaperones SCO1, SCO2, and COA6. This is a functionally relevant interaction in the context of CIV assembly, but the generic "protein binding" term is uninformative. Reason: While the interaction with COX16 is genuine and functionally relevant (COX16 promotes COX2 metallation), the generic "protein binding" term does not capture the biological significance of this interaction. The interaction is better represented by SCO2's role in CIV assembly (GO:0033617). Protein binding is uninformative per GO curation guidelines. Supporting Evidence: PMID:29381136 COX16, a protein required for cytochrome c oxidase assembly, interacts specifically with newly synthesized COX2 and its copper center-forming metallochaperones SCO1, SCO2, and COA6.
GO:0033617 mitochondrial respiratory chain complex IV assembly	IMP PMID:15229189 Human SCO1 and SCO2 have independent, cooperative functions ...	ACCEPT	Summary: This IMP annotation from Leary et al. (2004) is strongly supported. The study characterized the mitochondrial copper delivery pathway in SCO2 patient backgrounds and demonstrated that SCO2 patient cells have a defect in COX assembly with the appearance of a common assembly intermediate. This is direct mutant phenotype evidence for SCO2's role in CIV assembly. Reason: Strong experimental evidence (IMP) from a key functional study. Leary et al. showed that SCO2 mutations result in defective COX assembly and reduced levels of the mutant protein, with a specific assembly intermediate accumulating. This directly demonstrates SCO2's role in CIV assembly. Supporting Evidence: PMID:15229189 Immunoblot analysis of patient cell lines showed reduced levels of the mutant proteins, resulting in a defect in COX assembly, and the appearance of a common assembly intermediate.
GO:0005743 mitochondrial inner membrane	IDA PMID:15229189 Human SCO1 and SCO2 have independent, cooperative functions ...	ACCEPT	Summary: This IDA annotation from Leary et al. (2004) directly demonstrates SCO2 localization to the mitochondrial inner membrane. The study characterized the topology of SCO2 as a single-pass membrane protein with the N-terminus in the matrix and the C-terminal thioredoxin domain in the intermembrane space. Reason: Direct experimental evidence for mitochondrial inner membrane localization with topology determination. This is the primary experimental evidence for SCO2 localization and is at the correct level of specificity. Supporting Evidence: PMID:15229189 To investigate the molecular function of the SCO proteins, we characterized the mitochondrial copper delivery pathway in SCO1 and SCO2 patient backgrounds. ...Size exclusion chromatography suggests that both the proteins function as homodimers.
GO:0015035 protein-disulfide reductase activity	IDA PMID:19336478 Human SCO2 is required for the synthesis of CO II and as a t...	MODIFY	Summary: This IDA annotation from Leary et al. (2009) reports that SCO2 acts as a thiol-disulfide oxidoreductase for SCO1. Specifically, the paper demonstrates that SCO2 regulates the redox state of the copper-coordinating cysteines in SCO1, and that overexpression or knockdown of SCO2 alters the ratio of oxidized to reduced cysteines in SCO1. However, the paper specifically states that SCO2 acts to OXIDIZE the copper-coordinating cysteines in SCO1 (thiol-disulfide oxidoreductase), whereas GO:0015035 (protein-disulfide reductase activity) is defined as reduction of disulfide bonds. The directionality of the redox reaction may be more nuanced than the GO term captures. More recent reviews (Swaminathan & Gohil, 2022) describe a complex redox relay where COA6 reduces SCO proteins. Reason: The annotation captures an important secondary molecular function of SCO2, but the specific GO term may not precisely match the described activity. PMID:19336478 states SCO2 acts as a "thiol-disulphide oxidoreductase to oxidize the copper-coordinating cysteines in SCO1." The GO term GO:0015035 describes reductase activity (reduction of disulfide bonds), while the paper describes oxidoreductase activity in the oxidizing direction. A more appropriate term would be the broader GO:0015036 (disulfide oxidoreductase activity) which encompasses both directions. Proposed replacements: disulfide oxidoreductase activity Supporting Evidence: PMID:19336478 SCO2 acts as a thiol-disulphide oxidoreductase to oxidize the copper-coordinating cysteines in SCO1 during CO II maturation. file:human/SCO2/SCO2-deep-research-falcon.md SCO2 functions within a redox-sensitive copper-relay module...acting primarily through thiol-disulfide redox chemistry on cysteine pairs required to coordinate Cu in COX2 and SCO proteins
GO:0005515 protein binding	IPI PMID:24403053 Human COX20 cooperates with SCO1 and SCO2 to mature COX2 and...	MARK AS OVER ANNOTATED	Summary: This IPI annotation records the interaction between SCO2 and COX20 (Q5RI15, also known as FAM36A) demonstrated in PMID:24403053. COX20 acts as a chaperone that stabilizes newly synthesized COX2 and presents it to the SCO1/SCO2 metallochaperone module. The interaction is functionally significant for CIV assembly but the generic "protein binding" term is uninformative. Reason: The interaction with COX20 is genuine and functionally important (COX20 presents COX2 to the SCO metallochaperone module), but "protein binding" is uninformative per GO curation guidelines. The functional significance is better captured by the CIV assembly annotation (GO:0033617). Supporting Evidence: PMID:24403053 We propose that COX20 acts as a chaperone in the early steps of COX2 maturation, stabilizing the newly synthesized protein and presenting COX2 to its metallochaperone module, which in turn facilitates the incorporation of mature COX2 into the CIV assembly line.
GO:0005515 protein binding	IPI PMID:28330871 Human mitochondrial cytochrome c oxidase assembly factor COX...	MARK AS OVER ANNOTATED	Summary: This IPI annotation records the interaction between SCO2 and COX20 (Q5RI15) from Bourens & Barrientos (2017). The paper demonstrates that after COX18 promotes translocation of the COX2 C-tail, the SCO1-SCO2-COA6 copper metallation module binds to COX2-COX20 to finalize COX2 biogenesis. This is a duplicate interactor (COX20) from a different publication. Reason: Same issue as the other protein binding annotations -- the generic "protein binding" term is uninformative. The interaction with COX20 is genuine and important for CIV assembly but is better captured by the assembly process annotation. This is a second independent publication confirming the SCO2-COX20 interaction, but "protein binding" remains uninformative. Supporting Evidence: PMID:28330871 The release of COX18 from this complex coincides with the binding of the SCO1-SCO2-COA6 copper metallation module to COX2-COX20 to finalize COX2 biogenesis.
GO:0005515 protein binding	IPI PMID:29154948 The mitochondrial TMEM177 associates with COX20 during COX2 ...	MARK AS OVER ANNOTATED	Summary: This IPI annotation records interactions between SCO2 and both TMEM177 (Q53S58) and COX20 (Q5RI15) from Lorenzi et al. (2018). The paper shows that TMEM177 associates with newly synthesized COX2 and SCO2 in a COX20-dependent manner, and that SCO2 was found in a complex with TMEM177, COX20, COA6, MT-CO2, COX18, and SCO1. The GOA has two separate rows for this PMID. Both interactions are functionally relevant to the COX2 assembly pathway. Reason: Generic "protein binding" is uninformative per GO curation guidelines. The interactions with TMEM177 and COX20 are genuine and functionally relevant to CIV assembly, but are better captured by the assembly process annotation (GO:0033617). Supporting Evidence: PMID:29154948 TMEM177 associates with newly synthesized COX2 and SCO2 in a COX20-dependent manner
GO:0005515 protein binding	IPI PMID:25959673 Cooperation between COA6 and SCO2 in COX2 maturation during ...	MARK AS OVER ANNOTATED	Summary: This IPI annotation records the interaction between SCO2 and COA6 (Q5JTJ3) demonstrated in Pacheu-Grau et al. (2015). COA6 was shown to interact with SCO2 and pathogenic mutations in each protein affect complex formation. COA6 is a constituent of the mitochondrial copper relay system and cooperates with SCO2 in COX2 maturation. This is a highly significant functional interaction, but "protein binding" is still uninformative. Reason: Generic "protein binding" is uninformative. The interaction with COA6 is one of the most functionally significant interactions for SCO2 -- COA6 cooperates with SCO2 in COX2 metallation and acts as a disulfide reductase in the copper relay. But the term "protein binding" does not capture this. The functional significance is better represented by the assembly annotation. Supporting Evidence: PMID:25959673 We show that COA6 and SCO2 interact and that corresponding pathogenic mutations in each protein affect complex formation
GO:0001654 eye development	IMP PMID:23643385 Mutations in SCO2 are associated with autosomal-dominant hig...	KEEP AS NON CORE	Summary: This IMP annotation is based on Tran-Viet et al. (2013) who identified SCO2 mutations in families with autosomal-dominant high-grade myopia (MYP6). The paper showed that SCO2 mRNA levels were significantly downregulated in myopic mouse retinae and that SCO2 protein localizes to retina, retinal pigment epithelium, and sclera. However, the connection between SCO2's core function (mitochondrial copper chaperone for CIV) and eye development is indirect. The myopia phenotype likely reflects a tissue-specific consequence of mitochondrial dysfunction rather than a direct role in eye development. Reason: SCO2 mutations are associated with high-grade myopia, and SCO2 protein is expressed in the eye. However, this represents a pleiotropic effect of mitochondrial dysfunction on eye tissue rather than a direct role in eye development. SCO2 is not an eye development gene per se; it is a mitochondrial assembly factor whose loss has tissue-specific consequences including in the eye. Keeping as non-core to document the clinical association while accurately representing that this is not the core function. Supporting Evidence: PMID:23643385 Messenger RNA levels of SCO2 were significantly downregulated in myopic mouse retinae. Immunohistochemistry in mouse eyes confirmed SCO2 protein localization in retina, retinal pigment epithelium, and sclera.
GO:0030016 myofibril	IDA PMID:20864674 Unexpected vascular enrichment of SCO1 over SCO2 in mammalia...	MARK AS OVER ANNOTATED	Summary: This IDA annotation from Brosel et al. (2010) is based on immunohistochemistry of mouse tissues showing SCO2 expression patterns. The paper focused primarily on the differential tissue expression of SCO1 vs SCO2, showing that SCO2 is highly expressed in muscle (the tissue most affected in SCO2 patients) while SCO1 predominates in liver and vasculature. The myofibril localization is surprising for a mitochondrial inner membrane protein and likely reflects mitochondrial localization within muscle fibers rather than true myofibril localization. This annotation was made by MGI (mouse annotation transferred to human). Reason: SCO2 is an integral mitochondrial inner membrane protein. Its detection in myofibrils by immunohistochemistry more likely reflects the abundance of mitochondria in muscle tissue (where SCO2 is highly expressed) rather than true localization to the myofibril contractile apparatus. The paper was primarily about tissue expression patterns, not subcellular localization beyond mitochondria. The localization to the myofibril compartment is likely an artifact of the resolution of immunohistochemistry in muscle tissue. Supporting Evidence: PMID:20864674 the expression of SCO1, but not of SCO2, is very high in liver (the tissue most affected in SCO1-mutant patients), whereas the reverse holds true in muscle (the tissue most affected in SCO2-mutant patients).
GO:0005507 copper ion binding	NAS PMID:10545952 Fatal infantile cardioencephalomyopathy with COX deficiency ...	ACCEPT	Summary: This NAS annotation for copper ion binding is based on the founding SCO2 disease paper (PMID:10545952). The paper identified SCO2 as a homolog of yeast Sco1/2 which are known copper-binding proteins. While the paper did not directly assay copper binding by human SCO2, the inference from yeast homologs was correct and subsequently confirmed by NMR structure (PMID:17850752). The NAS evidence is appropriate for the time of annotation. Reason: Copper ion binding is a core molecular function of SCO2, confirmed by structural studies. This NAS annotation correctly inferred the function from the yeast homolog. The annotation is a duplicate of the IEA annotation from InterPro but from a different evidence source. Supporting Evidence: PMID:10545952 SCO2, a COX assembly gene...In yeast, two related COX assembly genes, SCO1 and SCO2 (for synthesis of cytochrome c oxidase), enable subunits I and II to be incorporated into the holoprotein.
GO:0005739 mitochondrion	TAS PMID:10545952 Fatal infantile cardioencephalomyopathy with COX deficiency ...	ACCEPT	Summary: This TAS annotation for mitochondrial localization is from the founding SCO2 disease paper (PMID:10545952). The paper identified SCO2 as a mitochondrial gene (yeast Sco1/Sco2 are mitochondrial) and showed that mutations cause COX deficiency with loss of mtDNA-encoded COX subunits, implying a mitochondrial function. Subsequent studies directly confirmed mitochondrial localization (PMID:15229189). Reason: Correct localization annotation. Mitochondrial localization was implicit in the founding paper and subsequently confirmed experimentally. TAS evidence is appropriate. Supporting Evidence: PMID:10545952 In yeast, two related COX assembly genes, SCO1 and SCO2 (for synthesis of cytochrome c oxidase), enable subunits I and II to be incorporated into the holoprotein.

Gene Description

Existing Annotations Review

Core Functions

SCO2 is a mitochondrial copper metallochaperone and assembly factor that enables copper relay into the CuA maturation pathway of COX2 during Complex IV biogenesis. Its core role is copper chaperone activity coupled to respiratory chain Complex IV assembly at the mitochondrial inner membrane.

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