| Evidence category | Finding | Experimental context/system | Source (authors year journal) | URL/DOI |
|---|---|---|---|---|
| Function/reaction | **sucA (PP_4189)** in *Pseudomonas putida* KT2440 is identified as the **E1 component of 2-oxoglutarate dehydrogenase (α-ketoglutarate dehydrogenase)**, a **ThDP-dependent** enzyme in the 2-oxoglutarate dehydrogenase complex. The complex converts **2-oxoglutarate + CoA + NAD+ → succinyl-CoA + CO2 + NADH**. (pqac-00000000, pqac-00000001, pqac-00000010, pqac-00000012) | KT2440 gene assignment from mutant study; broader bacterial OGDHc mechanism from reviews/enzymology papers | Avendaño et al. 2023 *Microbial Biotechnology*; Geiger 2019; Chakraborty et al. 2022 *Reactions*; Bunik et al. 2013 *Current Chemical Biology* | https://doi.org/10.1111/1751-7915.14215; https://doi.org/10.3390/reactions3010011; https://doi.org/10.2174/2212796811307010008 |
| Function/reaction | The OGDH complex is a **multienzyme E1/E2/E3 assembly**: E1o/SucA performs ThDP-dependent decarboxylation and succinyl transfer to lipoyl groups on E2; E2 forms succinyl-CoA; E3 reoxidizes dihydrolipoamide using **FAD and NAD+**. Cofactors highlighted include **ThDP, lipoate, CoA, FAD, NAD+**, with E2 built on a 24-mer core and flexible lipoyl “swinging arm” domains for substrate channeling. (pqac-00000010, pqac-00000012, pqac-00000014) | Authoritative conceptual background from bacterial OGDHc reviews and engineering paper | Chakraborty et al. 2022 *Reactions*; Bunik et al. 2013 *Current Chemical Biology* | https://doi.org/10.3390/reactions3010011; https://doi.org/10.2174/2212796811307010008 |
| Pathway role | SucA is placed in the **Krebs/TCA cycle** as a key enzyme linking **2-oxoglutarate metabolism to succinyl-CoA formation**, i.e., a central node connecting carbon flow and redox generation. (pqac-00000000, pqac-00000002, pqac-00000015) | KT2440 mutant phenotype paper and stress proteomics; broader metabolic review | Avendaño et al. 2023 *Microbial Biotechnology*; Ainelo et al. 2019 *Toxins*; Bunik et al. 2013 *Current Chemical Biology* | https://doi.org/10.1111/1751-7915.14215; https://doi.org/10.3390/toxins11020103; https://doi.org/10.2174/2212796811307010008 |
| Pathway/operon context | In *P. putida* KT2440, **sucA** is reported in operon context with **sucB** and in broader TCA-linked transcriptional units that can include **sdh genes, sucAB, sucABCD, and lpdG**; the α-KGDH complex in this context comprises **SucA, SucB, and LpdG**. (pqac-00000003) | Transcript/operon analysis and RNA-regulation study in KT2440 | Geiger 2019 | n/a |
| Regulation | A conserved **sucA RNA motif / sucA-II motif** in the **5′ UTR** was proposed as a **cis-regulatory RNA** because structural elements overlap the ribosome-binding region; in KT2440, **two transcription start sites** were reported, including one about **110 nt upstream** of the ORF. (pqac-00000001, pqac-00000006) | Comparative RNA motif analysis and follow-up regulatory experiments | Geiger 2019 | n/a |
| Regulation | The small-molecule riboswitch model for sucA-II was **not validated**. A systematic screen of **55 candidates** and another screen of **109 ligands** failed to confirm a ligand-responsive riboswitch; instead, results suggest possible **protein-mediated regulation**. Candidate binders included **SucC/SucD** (possible operon-level feedback) and PP_4065, which increased RNA cleavage consistent with mRNA destabilization. (pqac-00000006, pqac-00000008, pqac-00000018) | In-line probing, RNA pulldown, RNase footprinting, reporter assays | Geiger 2019 | n/a |
| Regulation | In broader bacterial OGDHc, E1o/SucA is described as a **major physiological regulation target** and often **rate-limiting**; **ThDP** can act as both catalytic cofactor and allosteric regulator, and adenine nucleotides can modulate substrate binding. (pqac-00000012, pqac-00000014, pqac-00000015) | Review-level mechanistic/regulatory synthesis across bacterial systems | Bunik et al. 2013 *Current Chemical Biology* | https://doi.org/10.2174/2212796811307010008 |
| Phenotypes/stress links | In a KT2440 mutant collection studying selenium metabolism, the **sucA mutant (PP_4189)** showed a **very slight reduction in growth rate and biomass formation** and was among mutants with a slower growth rate than WT. The paper interprets this as consistent with sucA encoding a key Krebs cycle enzyme. (pqac-00000000) | KT2440 mutants grown with and without selenite during selenium nanoparticle studies | Avendaño et al. 2023 *Microbial Biotechnology* | https://doi.org/10.1111/1751-7915.14215 |
| Phenotypes/stress links | In the same KT2440 selenium study, **2-ketoglutarate/glutamate metabolism** involving **sucA** was implicated as important for **selenite reduction to elemental selenium/selenium nanoparticles**. The authors highlight sucA among genes connecting central metabolism to selenium transformation. (pqac-00000000) | Genetic and analytical study of aerobic selenite reduction | Avendaño et al. 2023 *Microbial Biotechnology* | https://doi.org/10.1111/1751-7915.14215 |
| Phenotypes/stress links | Under **GraT toxin** stress in *P. putida*, SucA protein abundance decreased together with other TCA enzymes, supporting a model of **repressed central carbon metabolism/TCA flux** during toxin-induced physiological reprogramming. (pqac-00000002, pqac-00000005) | Proteomics and metabolomics in ΔgraA strain where GraT toxin is active | Ainelo et al. 2019 *Toxins* | https://doi.org/10.3390/toxins11020103 |
| Quantitative data | In the GraT study, **SucA abundance decreased >2-fold** in the ΔgraA strain at **25 °C**; the extracted table gives a **fold change of -2.12** for SucA. Other TCA enzymes in the same branch also dropped (e.g., Idh **-2.87**, SucD **-2.52**), supporting coordinated repression of the isocitrate-to-succinate segment. (pqac-00000002, pqac-00000009) | Quantitative proteomics table from ΔgraA vs WT comparison | Ainelo et al. 2019 *Toxins* | https://doi.org/10.3390/toxins11020103 |
| Quantitative data | In the selenium study, growth/selenite experiments were carried out with **1 mM selenite**. Although OD differed, the authors reported **no CFU differences for at least 22 h** between WT and mutants under selenite, indicating that optical changes may reflect selenium nanoparticle formation rather than loss of viability. (pqac-00000000) | KT2440 WT and mutant comparison during selenite reduction | Avendaño et al. 2023 *Microbial Biotechnology* | https://doi.org/10.1111/1751-7915.14215 |
| Quantitative data | Stress-dependent RNA pulldown experiments for sucA-related RNA regulation reported changing numbers of specifically bound proteins: **5** specific proteins in rich medium vs **17** in osmotic shock; **3** in rich medium, **3** in carbon limitation, and **7** in nitrogen limitation; at low pH with glutamate, **147** proteins were detected before filtering. These data support condition-dependent post-transcriptional regulation hypotheses rather than a validated ligand riboswitch. (pqac-00000004) | RNA–protein pulldown under osmoshock, carbon limitation (**1 mM glucose**), nitrogen limitation (**6 mM NH4+**), and pH-shift conditions | Geiger 2019 | n/a |
| Mechanistic specificity | Conserved E1o/SucA active-site features implicated in substrate specificity include an **Arg505-containing loop** for recognition of the substrate **5-carboxylate** and conserved histidines (**His539, His579, His747, His1020**). Engineering of E1o residues **His260** and **His298** altered substrate recognition, demonstrating that E1 chemistry can be retuned for nonnative substrates. (pqac-00000011, pqac-00000014, pqac-00000016) | Structural/mutational enzymology in bacterial OGDHc systems | Chakraborty et al. 2022 *Reactions*; Bunik et al. 2013 *Current Chemical Biology* | https://doi.org/10.3390/reactions3010011; https://doi.org/10.2174/2212796811307010008 |


*Table: This table summarizes the main functional-annotation evidence for Pseudomonas putida KT2440 sucA (PP_4189; UniProt Q88FA9), covering enzymatic function, pathway placement, regulation, stress-linked phenotypes, and quantitative findings from the gathered literature.*