sucC (PA1588) encodes the beta subunit of succinyl-CoA synthetase (SCS, succinate--CoA ligase), which forms an alpha2beta2 heterotetramer with the SucD alpha subunit. SCS catalyses the only substrate-level phosphorylation step of the tricarboxylic acid cycle, converting succinyl-CoA, phosphate and a nucleoside diphosphate to succinate, CoA and a nucleoside triphosphate. The beta subunit binds succinate and the nucleotide and determines nucleotide specificity; the alpha subunit carries the CoA and phosphate sites and the phosphohistidine intermediate. The P. aeruginosa enzyme, reconstituted from separately purified subunits, uses ADP and GDP about equally, can also make UTP and CTP, and transfers phosphate between ATP and GDP. It copurifies with nucleoside diphosphate kinase, and association with the 12-kDa form of Ndk shifts NTP output towards GTP and UTP, which has been proposed to feed GTP into alginate synthesis in mucoid strains.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000287 magnesium ion binding | IEA GO_REF:0000104 | KEEP AS NON CORE | Summary: Mg2+ cofactor binding from the HAMAP rule MF_00558. Reason: SCS needs one Mg2+ per subunit (HAMAP). Correct, but a cofactor-binding term peripheral to the ligase function. Supporting Evidence: file:PSEAE/sucC/sucC-uniprot.txt Note=Binds 1 Mg(2+) ion per subunit. |
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: Root catalytic activity from InterPro. Reason: Entailed by the accepted succinate-CoA ligase (ADP- and GDP-forming) activities. |
| GO:0004550 nucleoside diphosphate kinase activity | IDA PMID:10671455 Succinyl coenzyme A synthetase of Pseudomonas aeruginosa wit... | MARK AS OVER ANNOTATED | Summary: Purified SCS transferred the gamma-phosphate of ATP to GDP (and of GTP to ADP) without succinyl-CoA, an NDP kinase-like side reaction. Reason: Full text read. The reaction is real in vitro, probably through the alpha-subunit phosphohistidine, but its physiological relevance is unknown, and P. aeruginosa has a dedicated nucleoside diphosphate kinase (ndk). Much of what the paper calls "NDP kinase activity" is the normal SCS reaction run with different NDP acceptors, which the ligase terms already cover. Supporting Evidence: PMID:10671455 As shown in Fig. 4 A and B, the Scs complex transferred the terminal phosphate from [Ξ³- 32 P]ATP to GDP to form GTP |
| GO:0004775 succinate-CoA ligase (ADP-forming) activity | IBA GO_REF:0000033 | ACCEPT | Summary: ADP-forming SCS activity by IBA from PTN000212531; sound. Reason: Agrees with the direct evidence on this gene. The node is well curated: the GTP-specific SUCLG2 clade carries a NOT at PTN000929335. P53593 among the sources reflects its own IDA. Supporting Evidence: PMID:10671455 In the presence of inorganic orthophosphate, succinyl-CoA, and an equimolar amount of ADP and GDP, Scs synthesizes essentially an equimolar amount of ATP and GTP. |
| GO:0004775 succinate-CoA ligase (ADP-forming) activity | IDA PMID:10671455 Succinyl coenzyme A synthetase of Pseudomonas aeruginosa wit... | ACCEPT | Summary: PseudoCAP IDA, a seed of the PTN000212531 IBD. A mixture of purified SucC and SucD converted succinate, CoA and ATP to succinyl-CoA and made ATP from succinyl-CoA, Pi and ADP. Reason: Full text read. The activity was reconstituted from the purified beta and alpha subunits and assayed in both directions. The beta subunit holds the nucleotide and succinate sites, so "enables" is right for SucC as a subunit of the catalytic complex. Supporting Evidence: PMID:10671455 In this reaction the Scs enzyme converted succinate, CoA, and [Ξ³- 32 P]ATP to succinyl-CoA, ADP, and P i . PMID:10671455 In the presence of inorganic orthophosphate, succinyl-CoA, and an equimolar amount of ADP and GDP, Scs synthesizes essentially an equimolar amount of ATP and GTP. |
| GO:0004775 succinate-CoA ligase (ADP-forming) activity | IEA GO_REF:0000120 | ACCEPT | Summary: EC 6.2.1.5 / Rhea mapping; consistent with direct evidence. Reason: Supported by the reconstituted-enzyme assays of PMID:10671455. Supporting Evidence: file:PSEAE/sucC/sucC-uniprot.txt Reaction=succinate + ATP + CoA = succinyl-CoA + ADP + phosphate; |
| GO:0004776 succinate-CoA ligase (GDP-forming) activity | EXP PMID:10671455 Succinyl coenzyme A synthetase of Pseudomonas aeruginosa wit... | ACCEPT | Summary: GDP-forming activity. The P. aeruginosa enzyme makes GTP from succinyl-CoA, Pi and GDP as readily as ATP. Reason: Full text read. The enzyme is dual-specificity, so both the ADP- and GDP-forming terms are core. Supporting Evidence: PMID:10671455 In the presence of inorganic orthophosphate, succinyl-CoA, and an equimolar amount of ADP and GDP, Scs synthesizes essentially an equimolar amount of ATP and GTP. |
| GO:0004776 succinate-CoA ligase (GDP-forming) activity | IEA GO_REF:0000120 | ACCEPT | Summary: Rhea mapping for the GTP-forming reaction; supported by experiment. Reason: Consistent with the EXP row from PMID:10671455. Supporting Evidence: file:PSEAE/sucC/sucC-uniprot.txt Reaction=GTP + succinate + CoA = succinyl-CoA + GDP + phosphate; |
| GO:0005524 ATP binding | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: ATP binding. The beta subunit carries the ATP-grasp nucleotide site. Reason: Correct (ATP-grasp domain, and the beta subunit determines nucleotide specificity), but a substrate-binding term subsumed in the catalytic activity. Supporting Evidence: file:PSEAE/sucC/sucC-uniprot.txt The beta subunit provides nucleotide specificity of the enzyme and binds the substrate succinate |
| GO:0005829 cytosol | IBA GO_REF:0000033 | ACCEPT | Summary: Cytosol, by IBA from the E. coli SucC seed at PTN000212645. Reason: Bacterial SCS is a soluble cytoplasmic TCA cycle enzyme. No targeting signal, and the location of the E. coli ortholog transfers. Supporting Evidence: file:PSEAE/sucC/sucC-uniprot.txt Succinyl-CoA synthetase functions in the citric acid cycle (TCA), coupling the hydrolysis of succinyl-CoA to the synthesis of either ATP or GTP |
| GO:0006099 tricarboxylic acid cycle | IBA GO_REF:0000033 | ACCEPT | Summary: TCA cycle, by IBA; the core process of SCS. Reason: SCS catalyses the substrate-level phosphorylation step of the TCA cycle. The node seeds are experimentally characterised SCS subunits. Supporting Evidence: file:PSEAE/sucC/sucC-uniprot.txt Succinyl-CoA synthetase functions in the citric acid cycle (TCA), coupling the hydrolysis of succinyl-CoA to the synthesis of either ATP or GTP |
| GO:0006099 tricarboxylic acid cycle | IEA GO_REF:0000120 | ACCEPT | Summary: TCA cycle from InterPro/UniRule/UniPathway; consistent with the IBA. Reason: Same claim as the IBA row. Supporting Evidence: file:PSEAE/sucC/sucC-uniprot.txt Succinyl-CoA synthetase functions in the citric acid cycle (TCA), coupling the hydrolysis of succinyl-CoA to the synthesis of either ATP or GTP |
| GO:0006104 succinyl-CoA metabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: Succinyl-CoA metabolic process, by IBA. Reason: SCS interconverts succinyl-CoA and succinate, so the term is accurate. It is not an ancestor of the TCA cycle term, so it is not redundant. Supporting Evidence: PMID:10671455 In this reaction the Scs enzyme converted succinate, CoA, and [Ξ³- 32 P]ATP to succinyl-CoA, ADP, and P i . |
| GO:0009142 nucleoside triphosphate biosynthetic process | IDA PMID:10671455 Succinyl coenzyme A synthetase of Pseudomonas aeruginosa wit... | KEEP AS NON CORE | Summary: NTP biosynthesis. The enzyme generates ATP, GTP, UTP and CTP from succinyl-CoA, Pi and the corresponding NDPs. Reason: Full text read. The reaction products are NTPs, so the term is true. NTP supply is a consequence of the TCA step rather than the gene's main process, so the row is non-core. Supporting Evidence: PMID:10671455 In the presence of inorganic orthophosphate (P(i)), succinyl-CoA, and either GDP, ADP, UDP or CDP, it synthesizes GTP, ATP, UTP, or CTP. |
| GO:0042709 succinate-CoA ligase complex | IBA GO_REF:0000033 | ACCEPT | Summary: SCS complex membership, by IBA from PTN000212531. Reason: Agrees with the reconstitution evidence on this gene and with the HAMAP subunit statement; P53593 among the sources reflects its own IDA. Supporting Evidence: file:PSEAE/sucC/sucC-uniprot.txt Heterotetramer of two alpha and two beta subunits. |
| GO:0042709 succinate-CoA ligase complex | IDA PMID:10671455 Succinyl coenzyme A synthetase of Pseudomonas aeruginosa wit... | ACCEPT | Summary: PseudoCAP IDA, a seed of the PTN000212531 complex IBD. SCS activity required the mixture of separately purified SucC and SucD. Reason: Full text read. The complex was not isolated as such, but activity reconstituted only from the mixed subunits is direct functional evidence that SucC acts as part of the alpha/beta SCS complex. Supporting Evidence: PMID:10671455 In order to test the activity of Scs Ξ² subunit, an Scs enzymatic reaction was performed with succinate, CoA, and a mixture of purified Scs Ξ± and Ξ² subunits (3 ΞΌg each) in the presence of [Ξ³- 32 P]ATP. |
| GO:0042709 succinate-CoA ligase complex | IEA GO_REF:0000117 | ACCEPT | Summary: SCS complex from ARBA; same claim as the IDA and IBA rows. Reason: Consistent with the experimental and phylogenetic rows. Supporting Evidence: file:PSEAE/sucC/sucC-uniprot.txt Heterotetramer of two alpha and two beta subunits. |
| GO:0046777 protein autophosphorylation | IDA PMID:10671455 Succinyl coenzyme A synthetase of Pseudomonas aeruginosa wit... | REMOVE | Summary: Protein autophosphorylation. The labelled protein in the assay is the 30-kDa SucD alpha subunit (catalytic phosphohistidine), not SucC. Reason: Full text read. The paper detects phosphorylation of the 30-kDa alpha subunit, which is the phosphoenzyme intermediate of the SCS reaction. The 40-kDa beta subunit (this gene) is not reported to be phosphorylated. A catalytic phosphohistidine intermediate is part of the ligase reaction, not a protein autophosphorylation process. Supporting Evidence: PMID:10671455 A 5 ΞΌM concentration of GDP in the reaction mixture stimulated the phosphorylation of the 30-kDa Scs Ξ± subunit, whereas 50 ΞΌM GDP in the reaction mixture showed a significant decrease. |
| GO:0046872 metal ion binding | IEA GO_REF:0000002 | TOO GENERAL | Summary: Generic metal ion binding from InterPro. Reason: Entailed by the magnesium ion binding row kept in this review. |
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Download this section (compressed HTML)Q: Does association with the 12-kDa membrane form of Ndk shift SCS nucleotide output in vivo, and does that contribute measurably to GTP supply for alginate synthesis?
Experiment: Measure ATP versus GTP formation by purified SucCD with physiological nucleotide pools, and assess alginate production in a sucC mutant with complementation.
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