sucA (PP_4189) encodes the E1 component (2-oxoglutarate dehydrogenase, EC 1.2.4.2) of the 2-oxoglutarate dehydrogenase complex (OGDHc; also called the alpha-ketoglutarate dehydrogenase complex, KGDH). Together with the E2 dihydrolipoyl succinyltransferase (SucB) and the E3 dihydrolipoyl dehydrogenase (LpdG), SucA catalyzes the oxidative decarboxylation of 2-oxoglutarate to succinyl-CoA, releasing CO2 and reducing NAD+ to NADH. SucA performs the first, thiamine-diphosphate (ThDP)-dependent step, decarboxylating 2-oxoglutarate and transferring the resulting succinyl moiety to the lipoyl group carried on the E2 component. This reaction is an irreversible step of the tricarboxylic acid (TCA) cycle and a major node connecting carbon, nitrogen (via 2-oxoglutarate/glutamate), and redox metabolism. The OGDH complex is a large, soluble multienzyme assembly located in the cytoplasm of bacteria.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004591 oxoglutarate dehydrogenase (succinyl-transferring) activity | IEA GO_REF:0000120 | ACCEPT | Summary: Core molecular function. This is the E1 enzymatic activity (EC 1.2.4.2) of the OGDH complex, matching the UniProt RecName and domain architecture (TPP_E1_OGDC-like CDD, IPR011603 2-oxoglutarate_DH_E1). Although IEA, this is strongly supported by family/EC assignment and the conserved domain set. |
| GO:0005829 cytosol | IEA GO_REF:0000118 | ACCEPT | Summary: The bacterial OGDH complex is a soluble cytoplasmic assembly of central carbon metabolism. The annotation is consistent with the known localization, though the GO term "cytosol" (GO:0005829) is the term applied by TreeGrafter. |
| GO:0006099 tricarboxylic acid cycle | IEA GO_REF:0000118 | ACCEPT | Summary: Core biological process. The OGDH complex catalyzes the 2-oxoglutarate to succinyl-CoA step of the TCA cycle. Well supported for this gene in P. putida KT2440 (sucA = PP_4189 repeatedly identified as a key Krebs cycle enzyme). |
| GO:0016624 oxidoreductase activity, acting on the aldehyde or oxo group of donors, disulfide as acceptor | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: This is a parent/more general molecular function term covering the E1 oxidoreductase chemistry (oxo-group donor, lipoyl-disulfide acceptor). It is not wrong, but it is a less informative generalization of the specific E1 activity already captured by GO:0004591. Keeping as non-core to avoid redundancy with the precise term. |
| GO:0030976 thiamine pyrophosphate binding | IEA GO_REF:0000002 | ACCEPT | Summary: SucA is a ThDP (thiamine diphosphate)-dependent decarboxylase; the UniProt cofactor annotation lists thiamine diphosphate, and the InterPro signature (IPR011603, THDP-binding fold) supports this. Accept as a supporting molecular function. |
| GO:0045252 oxoglutarate dehydrogenase complex | IEA GO_REF:0000118 | ACCEPT | Summary: Correct cellular component. SucA is the E1 component and a structural part of the OGDH complex (with SucB/E2 and LpdG/E3). Operon-context evidence in KT2440 places sucA with sucB and lpdG. |
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