CYC1

Summary: Cytochrome c is a core electron carrier protein that shuttles electrons between Complex III and Complex IV in the mitochondrial electron transport chain. The IBA evidence is appropriate for this molecular function annotation.

Reason: This is the quintessential function of cytochrome c. UniProt describes CYC1 as an electron carrier protein where the heme group accepts electrons from cytochrome c1 and transfers them to cytochrome c oxidase. Both IDA evidence from PMID:7851399 and PMID:18975895 directly support electron transfer activity through kinetic measurements and electrochemical analysis. IBA annotation is appropriate given the highly conserved nature of this function across cytochrome c family members (PTHR11961). This represents a core primary metabolic role.

Summary: Cytochrome c is the direct electron acceptor from Complex III, receiving electrons from ubiquinol and transferring them to Complex IV. This biological process annotation accurately describes CYC1's participation in the electron transport chain.

Reason: This annotation correctly identifies CYC1's specific role in mitochondrial electron transport. CYC1 is the electron acceptor from ubiquinol-cytochrome c oxidoreductase (Complex III, the cytochrome bc1 complex). UniProt FUNCTION states CYC1 accepts electrons from the heme group of cytochrome c1 of ubiquinol-cytochrome c oxidoreductase. IDA evidence from PMID:7851399 characterizes the kinetic properties of cytochrome c as a substrate, demonstrating this electron transport step. This is a core primary metabolic function.

Summary: Cytochrome c is localized to the mitochondrial intermembrane space (IMS), the aqueous compartment between the inner and outer mitochondrial membranes, where it functions as an electron shuttle between membrane-bound protein complexes.

Reason: This is the correct cellular compartment localization for CYC1. UniProt explicitly states SUBCELLULAR LOCATION is Mitochondrion intermembrane space. PMID:9866716 describes the purification of intermembrane space fractions with cytochrome c as a key marker protein. IBA annotation is appropriate given the universal localization of cytochrome c to the IMS across eukaryotes.

Summary: Cytochrome c donates electrons to Complex IV (cytochrome c oxidase), where oxygen serves as the final electron acceptor. This biological process annotation describes the second major step of CYC1's participation in the electron transport chain.

Reason: This annotation correctly identifies CYC1's specific role as the electron donor to cytochrome c oxidase (Complex IV). UniProt states CYC1 transfers electrons to the dinuclear copper A center of the COX2 subunit of cytochrome oxidase, the final protein carrier in the mitochondrial electron-transport chain. PMID:7851399 provides kinetic evidence for this interaction. IBA annotation is appropriate. This is a core primary metabolic function.

Summary: IEA annotation of mitochondrial intermembrane space localization derived from automated sequence analysis and subcellular location databases. Consistent with experimental evidence.

Reason: IEA annotation correctly predicts CYC1 localization based on UniProt subcellular location annotations. This is fully supported by experimental IDA evidence (PMID:9866716). Redundant with other mitochondrial intermembrane space annotations but acceptable as it represents automated annotation pipelines that independently confirm the localization.

Summary: IEA annotation by ARBA machine learning model predicting CYC1 involvement in ubiquinol-to-cytochrome c electron transport. Consistent with experimental evidence and core function.

Reason: IEA annotation correctly predicts this core metabolic process based on sequence homology and association rules. Fully consistent with experimental IDA evidence (PMID:7851399) and IBA annotations. ARBA models are trained on well-characterized annotations, and this prediction is mechanistically sound for the cytochrome c family.

Summary: IEA annotation by ARBA machine learning model predicting CYC1 involvement in cytochrome c-to-oxygen electron transport. Consistent with experimental evidence and core function.

Reason: IEA annotation correctly predicts this core metabolic process based on sequence homology and association rules. Fully consistent with experimental IDA evidence (PMID:7851399) and IBA annotations. ARBA models work well for well-characterized metabolic processes like the electron transport chain.

Summary: IEA annotation of electron transfer activity derived from combined automated methods and InterPro domain analysis. Represents predicted molecular function based on heme-binding domain membership.

Reason: IEA annotation correctly predicts electron transfer activity based on InterPro domain membership (IPR002327, IPR009056, IPR036909 - cytochrome c domains). This is the most direct inference from sequence structure. Fully supported by multiple IDA evidence entries. IEA based on protein family membership is appropriate for such well-characterized functions.

Summary: Heme binding activity inferred from InterPro domain analysis of cytochrome c protein structure. CYC1 contains covalent heme c group essential for electron transfer.

Reason: IEA annotation based on InterPro domain membership correctly identifies heme binding as a molecular function of CYC1. UniProt explicitly states CYC1 binds 1 heme c group covalently per subunit, with covalent binding at His-18 and His-81 and axial iron coordination by His-86 and Met-80. This molecular function is fundamental to the redox chemistry enabling electron transfer. IEA from protein family annotation is appropriate for this well-characterized feature.

Summary: Respiratory electron transport chain participation inferred from UniProtKB keyword mapping. CYC1 is a component of the electron transport chain that couples redox reactions to ATP synthesis.

Reason: IEA annotation based on UniProtKB-KW (keyword) mapping correctly identifies CYC1 as a component of the respiratory electron transport chain. UniProt keywords include Respiratory chain and Electron transport, reflecting CYC1's role as a central hub between Complexes III and IV. This is appropriate for identifying participation in the broader pathway context while more specific electron transport processes are annotated separately.

Summary: Metal ion binding inferred from UniProtKB keyword mapping (KW-0479) reflecting the iron coordination in CYC1's heme c group. The Fe center is essential for redox cycling.

Reason: IEA annotation based on UniProtKB keyword mapping correctly identifies metal ion binding as a molecular function. CYC1 binds iron (Fe) as the central atom of heme c through axial coordination by His-86 and Met-80, as documented in UniProt feature annotation. This is a more general annotation than GO:0020037 (heme binding) but appropriately identifies the metal cofactor requirement. For a protein with such well-characterized iron coordination, IEA from keyword mapping is justified.

Summary: Cytochrome c peroxidase (CCP) interaction demonstrated through structural and kinetic studies of the electron transfer complex. This represents a secondary protein-protein interaction not central to CYC1's primary metabolic role.

Reason: While CYC1 does interact with cytochrome c peroxidase (CCP) as demonstrated by PMID:15071191, the generic term protein binding is not informative and represents an over-annotation. The CCP interaction is a non-physiological interaction used for research purposes. More importantly, the physiological protein interactions with Complex III (cytochrome c1) and Complex IV (cytochrome c oxidase subunit IV) are far more significant but already captured by the electron transport process annotations. A vague protein binding term obscures rather than clarifies the functional role. For a protein with such well-defined biochemistry, more specific binding terms would be preferable if capturing this interaction is important. CCP interaction should not be prioritized over the core metabolic functions.

Summary: Electron transfer between cytochrome c and cytochrome c peroxidase in single crystals. IPI evidence for protein-protein interaction with CCP.

Reason: PMID:15339156 studies electron transfer kinetics between CYC1 and CCP in single crystal systems, demonstrating physical interaction. However, as with PMID:15071191, this CCP interaction is not central to CYC1's primary physiological role. The generic term protein binding is uninformative and represents an over-annotation. The critical physiological interactions are with Complex III and Complex IV proteins, already captured by process annotations. CCP is a research tool for studying electron transfer kinetics, not a core functional partner. This annotation should be deprioritized in favor of core metabolic functions.

Summary: Solution structure and dynamics of the complex between cytochrome c and cytochrome c peroxidase by paramagnetic NMR spectroscopy. IPI evidence for protein-protein interaction.

Reason: PMID:17146057 characterizes the complex between CYC1 and CCP using structural biology methods. However, this represents a non-physiological research interaction rather than a core functional interaction. The CCP is not a natural substrate or cofactor partner in yeast metabolism. The generic term protein binding is uninformative. More significant physiological protein interactions (Complex III and IV) are already represented in the electron transport process annotations. This annotation over-represents peripheral research interactions at the expense of core functions.

Summary: Cytochrome c peroxidase and cytochrome c encounter complex characterized through structural and kinetic studies.

Reason: PMID:24726731 characterizes the CCP-cytochrome c encounter complex. However, this remains a non-physiological research interaction with CCP, not a core functional partner. The generic protein binding term lacks specificity and represents peripheral rather than core function. CCP interactions, while scientifically interesting for studying electron transfer mechanisms, should not dominate the annotation profile of CYC1. The primary physiological interactions with Complex III (cytochrome c1) and Complex IV are more important and already captured in process annotations. This is over-annotation that dilutes focus on core metabolic role.

Summary: CYC1 binds to cardiolipin (CL), an anionic mitochondrial lipid, through electrostatic interactions mediated by lysine residues at site A. This interaction is relevant during apoptosis when CYC1 oxidizes CL.

Reason: PMID:30182710 provides direct experimental evidence (IDA) that CYC1 binds cardiolipin at multiple lysine residues (positions 72, 73, 86, 87). Cardiolipin binding is well-documented and mechanistically characterized. However, this represents a secondary function associated with apoptotic signaling rather than the primary aerobic metabolic role. In yeast under normal aerobic growth, cardiolipin binding relates to apoptotic peroxidase activity, not the primary electron transport function. For a primarily metabolic protein, this should be retained as a supported annotation but marked as non-core to distinguish from the central electron transport functions. The apoptotic role of CYC1 is less central in yeast compared to mammals.

Summary: CYC1 is a mitochondrial protein identified through large-scale mitochondrial proteomics analysis. HDA (homology-derived assertion) evidence from PMID:16823961 contributes to broader cellular component annotation.

Reason: HDA annotation correctly identifies CYC1 as a mitochondrial protein. PMID:16823961 is a large-scale proteomic analysis of the yeast mitochondrial proteome that identified CYC1 among intermembrane space proteins. However, GO:0005758 (mitochondrial intermembrane space) is more specific and informative than the broader GO:0005739 (mitochondrion). Both are technically correct, but the more specific localization is more useful. HDA annotation is appropriate for broad compartment classification, though the intermembrane space annotations are more precise and should be prioritized.

Summary: Direct experimental evidence that CYC1 is localized to the mitochondrial intermembrane space. PMID:9866716 describes the purification of distinct IMS fractions with CYC1 as a key marker protein.

Reason: IDA annotation provides direct experimental evidence for CYC1 localization. PMID:9866716 is a landmark study that fractionally purified mitochondrial intermembrane space content, identifying CYC1 as a defining marker of the salt-extractable IMS fraction. This is the most specific and accurate cellular localization, superior to the broader mitochondrion (GO:0005739) annotation. This is a core, well-supported annotation of CYC1's subcellular localization.

Summary: Direct kinetic and biochemical evidence that CYC1 functions in mitochondrial electron transport from ubiquinol to the final electron acceptor at Complex IV. PMID:7851399 characterizes kinetic properties of cytochrome c as a substrate for cytochrome c oxidase.

Reason: IDA annotation provides direct experimental evidence for CYC1's role in electron transport. PMID:7851399 is a seminal biochemical study characterizing the purified eleven-subunit cytochrome c oxidase complex with kinetic analysis of cytochrome c as a substrate. The demonstrated Km values and turnover numbers (1500 s-1) represent direct functional evidence that CYC1 participates in this electron transport step. This is a core primary metabolic function with the highest quality evidence.

Summary: Direct kinetic and biochemical evidence that CYC1 functions in mitochondrial electron transport from cytochrome c to the final electron acceptor (oxygen). PMID:7851399 characterizes kinetic properties of cytochrome c oxidase interaction with cytochrome c.

Reason: IDA annotation provides direct experimental evidence for CYC1's role as electron donor to cytochrome c oxidase. PMID:7851399 demonstrates quantitatively that cytochrome c is a substrate for Complex IV (cytochrome c oxidase), with measured kinetic parameters reflecting true enzyme kinetics. This electron transfer to oxygen is the final step in the respiratory chain and a core primary metabolic function of CYC1. This is one of the most important functional annotations for this protein.

Summary: Direct electrochemical evidence demonstrating electron transfer activity of yeast CYC1. PMID:18975895 measures electron transfer rate constants using surface-enhanced resonance Raman spectroscopy.

Reason: IDA annotation provides direct biophysical evidence for CYC1's electron transfer activity. PMID:18975895 employs sophisticated electrochemical methods to measure electron transfer rate constants (8-18 s-1) and demonstrates that protein reorientation is rate-limiting for interfacial electron transfer. This represents direct, quantitative molecular evidence of the electron transfer mechanism central to CYC1's function. This is a core primary molecular function with excellent experimental support.

Summary: Direct biochemical evidence for electron transfer activity through kinetic characterization of cytochrome c as a functional substrate in electron transport chain complexes.

Reason: IDA annotation provides direct biochemical evidence for electron transfer activity from a landmark kinetic analysis. PMID:7851399 demonstrates that cytochrome c functions as a true kinetic substrate for both Complex III (ubiquinol-cytochrome c oxidoreductase) and Complex IV (cytochrome c oxidase), with measured turnover numbers and Km values reflecting physiological kinetics. This dual IDA evidence from different experimental approaches (electrochemistry and enzyme kinetics) provides robust support for this fundamental molecular function.