sucC

Gene Description

sucC encodes the beta subunit of succinyl-CoA synthetase (succinate--CoA ligase [ADP-forming], EC 6.2.1.5), a core enzyme of the tricarboxylic acid (TCA) cycle. The active enzyme is a heterotetramer of two alpha (SucD) and two beta (SucC) subunits that catalyzes the reversible interconversion of succinyl-CoA + phosphate + NDP and succinate + CoA + NTP. This reaction is the only substrate-level phosphorylation step of the TCA cycle, conserving the thioester bond energy of succinyl-CoA as a nucleoside triphosphate (ATP and/or GTP). The beta subunit contributes the nucleotide specificity and substrate (succinate) binding, harbors an ATP-grasp fold, and binds Mg2+, while the CoA- and phosphate-binding sites reside in the alpha subunit. As a soluble cytosolic enzyme, it links carbon oxidation through the TCA cycle to energy conservation and, in the reverse direction, supplies succinyl-CoA for biosynthetic reactions.

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0000287 magnesium ion binding	IEA GO_REF:0000104	ACCEPT	Summary: Succinyl-CoA synthetase requires Mg2+ as a cofactor; UniProt annotates one Mg2+ per beta subunit with two binding residues (positions 199 and 213). Reason: Consistent with the HAMAP rule (MF_00558) cofactor statement and conserved Mg2+-binding residues in the ATP-grasp domain. Mg2+ is required for the kinase/ligase chemistry.
GO:0003824 catalytic activity	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: Root-level catalytic activity term; the specific succinate-CoA ligase activity is captured by more precise terms. Reason: GO:0003824 is an uninformative high-level term superseded by the specific GO:0004775 (succinate-CoA ligase (ADP-forming) activity) annotation. Not useful as a representation of the gene's function.
GO:0004775 succinate-CoA ligase (ADP-forming) activity	IEA GO_REF:0000120	ACCEPT	Summary: This is the canonical molecular function of SucC/SucD - EC 6.2.1.5, the ADP-forming succinate-CoA ligase, mapped via RHEA:17661 and EC:6.2.1.5. Reason: Core molecular function. Strongly supported by family/domain membership, HAMAP rule, and the explicit UniProt catalytic-activity statement. Represents the primary activity of the enzyme.
GO:0004776 succinate-CoA ligase (GDP-forming) activity	IEA GO_REF:0000116	ACCEPT	Summary: Bacterial succinyl-CoA synthetases, including this enzyme, can use GTP/GDP in addition to ATP/ADP; UniProt annotates the GDP-forming reaction (RHEA:22120) alongside the ADP-forming one. Reason: The HAMAP rule and UniProt record both list the GTP/GDP catalytic activity. Bacterial SCS enzymes are generally nucleotide-promiscuous, so retaining the GDP-forming activity is appropriate as part of the core function.
GO:0005524 ATP binding	IEA GO_REF:0000120	ACCEPT	Summary: The beta subunit ATP-grasp domain binds ATP; UniProt annotates multiple ATP-binding residues (e.g., 46, 53-55, 99, 102, 107). Reason: Directly supported by the ATP-grasp fold and conserved nucleotide-binding residues; the beta subunit provides nucleotide binding/specificity for the ligase reaction.
GO:0005829 cytosol	IEA GO_REF:0000118	ACCEPT	Summary: As a soluble TCA-cycle enzyme in a Gram-negative bacterium, SucC acts in the cytoplasm/cytosol. Reason: Consistent with the soluble, cytoplasmic localization expected for a bacterial TCA-cycle enzyme. No membrane or secretion signals are present.
GO:0006099 tricarboxylic acid cycle	IEA GO_REF:0000120	ACCEPT	Summary: Succinyl-CoA synthetase catalyzes the succinyl-CoA to succinate step, the substrate-level phosphorylation step of the TCA cycle. Reason: Core biological process. Well supported by enzyme family, pathway membership (UniPathway UPA00223), and HAMAP rule.
GO:0006104 succinyl-CoA metabolic process	IEA GO_REF:0000118	KEEP AS NON CORE	Summary: The enzyme directly interconverts succinyl-CoA and succinate, so it participates in succinyl-CoA metabolism. Reason: Accurate but a more general parent process that is subsumed by the specific TCA cycle role; retained as non-core. The succinate-CoA ligase activity and TCA cycle annotations are the primary representations.
GO:0042709 succinate-CoA ligase complex	IEA GO_REF:0000120	ACCEPT	Summary: SucC is the beta subunit of the succinate-CoA ligase complex, a heterotetramer of two alpha and two beta subunits. Reason: Correct cellular component / complex membership, supported by the UniProt SUBUNIT statement (heterotetramer of two alpha and two beta subunits).
GO:0046872 metal ion binding	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: General metal-ion binding term; the relevant metal here is Mg2+, captured specifically by GO:0000287. Reason: GO:0046872 is a generic parent of GO:0000287 (magnesium ion binding), which is the precise and informative annotation. The general term adds no information.

Gene Description

Existing Annotations Review

Core Functions

Catalyzes the reversible, Mg2+-dependent, nucleotide-coupled interconversion of succinyl-CoA and succinate (substrate-level phosphorylation step of the TCA cycle), as the beta subunit of the heterotetrameric succinyl-CoA synthetase.

References

Deep Research

Falcon

OpenScientist

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