The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The gene symbol sdhA in Pseudomonas putida KT2440 is unambiguously linked to PP_4191, annotated as the succinate dehydrogenase flavoprotein subunit (SdhA), and occurs with the other complex II subunits SdhB (PP_4190), SdhD (PP_4192), and SdhC (PP_4193) in KT2440. This mapping matches the UniProt-provided identity (Q88FA7) as a succinate dehydrogenase flavoprotein subunit (EC 1.3.5.1). (chavarria2012regulatorytasksof pages 3-4, chavarria2012regulatorytasksof media b14b64f4, chavarria2012regulatorytasksof media 8dabbe7d)
Succinate dehydrogenase (SDH; respiratory complex II) is a central bioenergetic enzyme that functionally couples the tricarboxylic acid (TCA) cycle to the aerobic respiratory electron transport chain. In bacteria and mitochondria, complex II comprises a soluble catalytic “head” and membrane anchor components that connect catalysis to the quinone pool. (bouillaud2023inhibitionofsuccinate pages 3-5, mcneil2012sdheisa pages 1-2)
Within this complex, SdhA is the flavoprotein catalytic subunit that carries the flavin cofactor and hosts the succinate/fumarate active-site chemistry. (bouillaud2023inhibitionofsuccinate pages 3-5, mcneil2012sdheisa pages 1-2)
The canonical SDH reaction (EC 1.3.5.1) is the oxidation of succinate to fumarate:
The electrons are transferred into the membrane quinone pool by coupled reduction of quinone:
Thus, SdhA’s primary substrate specificity is toward succinate (as the electron donor in the forward SDH direction) and fumarate (in the reverse fumarate reductase direction in organisms/conditions where reversal occurs), with coupling to the quinone pool as electron acceptor via the rest of complex II. (bouillaud2023inhibitionofsuccinate pages 3-5)
Complex II function depends on redox cofactors:
A key mechanistic concept for bacterial SdhA is flavinylation (incorporation/attachment of FAD into the SdhA subunit). In a bacterial model system, SdhA requires an accessory protein SdhE for FAD incorporation; SdhE interacts with SdhA, binds FAD, and is required for SdhA flavinylation and SDH activity. (mcneil2012sdheisa pages 4-5, mcneil2012sdheisa pages 1-2)
Although this SdhE-dependent maturation evidence is not from P. putida directly, SdhE is described as conserved across diverse proteobacteria, supporting inference that P. putida SdhA likewise depends on proper flavinylation for activity. (mcneil2012sdheisa pages 1-2)
Complex II is described as a membrane-spanning redox enzyme with a soluble catalytic side containing the flavoprotein subunit (SdhA) and membrane subunits that inject electrons into quinone in the membrane. (bouillaud2023inhibitionofsuccinate pages 3-5)
Consistent with this, bacterial experimental work localized SdhA to the membrane-associated complex, reflecting its function as part of a membrane respiratory complex rather than a freely soluble cytosolic enzyme. (mcneil2012sdheisa pages 4-5)
In KT2440, the complex II subunits are explicitly mapped as:
This supports annotation of PP_4191/Q88FA7 as the catalytic complex II flavoprotein subunit within the canonical SDH architecture in P. putida KT2440. (chavarria2012regulatorytasksof media b14b64f4, chavarria2012regulatorytasksof media 8dabbe7d)
A 2023 review synthesizes modern understanding of SDH/complex II as a redox enzyme connecting succinate oxidation to quinone reduction, emphasizing its four-subunit architecture and centrality to energy metabolism, while also discussing assay approaches and the energetic consequence that complex II does not pump protons (unlike complexes I/III/IV), implying its control is primarily redox/substrate/quinone-state dependent. (bouillaud2023inhibitionofsuccinate pages 3-5)
While this review focuses on SDH inhibition in eukaryotic contexts, its biochemical statements about the enzyme’s reaction chemistry and architecture are directly applicable to bacterial SDH (including P. putida). (bouillaud2023inhibitionofsuccinate pages 3-5)
A 2023 study on microaerobic cultivation of P. putida KT2440 for succinate production provides direct KT2440 evidence that:
Together, these findings operationalize sdhA (and sdhAB) as a tunable node in P. putida metabolic engineering for improved organic acid accumulation under oxygen-limited regimes. (mutyala2023citratesynthaseoverexpression pages 10-11)
Although 2024 P. putida KT2440 systems-biology papers were retrieved in the search set, the accessible text evidence obtained in this run did not provide explicit, citable sdhA-specific quantitative statements. Therefore, sdhA-focused 2023 KT2440 evidence (above) is the primary recent source for strain-specific regulation and application claims within the current tool-retrieved corpus. (mutyala2023citratesynthaseoverexpression pages 10-11)
In KT2440 succinate bioproduction under microaerobic conditions, sdhA/SDH is relevant because it can consume succinate (reassimilate it into the TCA cycle via succinate oxidation). The 2023 microaerobic cultivation study explicitly frames sdhAB as a target whose downregulation or deletion could improve succinate accumulation and yields in engineered strains. (mutyala2023citratesynthaseoverexpression pages 10-11)
This is a practical, real-world application: controlling SDH activity (via sdhA expression or function) helps redirect carbon and reducing equivalents away from respiration-driven succinate consumption toward product accumulation. (mutyala2023citratesynthaseoverexpression pages 10-11)
Multiple independent lines of evidence converge on the functional assignment:
Thus, even if KT2440-specific enzymology (e.g., purified enzyme kinetics) is limited in the retrieved corpus, functional inference for Q88FA7 is robust because complex II is highly conserved and anchored by direct strain-specific gene mapping. (bouillaud2023inhibitionofsuccinate pages 3-5, chavarria2012regulatorytasksof pages 3-4, chavarria2012regulatorytasksof media b14b64f4, chavarria2012regulatorytasksof media 8dabbe7d)
The KT2440 observation that sdhA transcript abundance drops ~2.2-fold under microaerobic cultivation can be interpreted as part of a broader physiological shift: when oxygen is limiting, cells may downshift electron transport chain activity and reduce flux through succinate oxidation, a step that normally passes electrons to quinone in aerobic respiration. (bouillaud2023inhibitionofsuccinate pages 3-5, mutyala2023citratesynthaseoverexpression pages 10-11)
In the same 2023 study (microaerobic succinate production from acetate with citrate synthase overexpression):
These values provide practical quantitative context for why minimizing SDH-mediated succinate reassimilation (e.g., via sdhAB modulation) is an attractive engineering strategy. (mutyala2023citratesynthaseoverexpression pages 10-11)
In a bacterial model system used to elucidate complex II flavinylation:
| Topic | Key findings (concise) | Evidence type (review/primary; organism) | Quantitative data (if any) | Primary source (authors, year) | Publication date (month/year if available) | URL | PaperQA citation id (pqac-...) |
|---|---|---|---|---|---|---|---|
| identity | PP_4191 is explicitly annotated as SdhA, succinate dehydrogenase flavoprotein subunit in Pseudomonas putida KT2440, matching UniProt Q88FA7. | Primary; P. putida KT2440 | Not reported | Chavarría et al., 2012 | 05/2012 | https://doi.org/10.1128/mbio.00028-12 | (chavarria2012regulatorytasksof pages 3-4) |
| reaction/EC | Succinate dehydrogenase (complex II) catalyzes succinate → fumarate + 2H+ + 2e− and couples this to quinone reduction (Q → QH2), consistent with EC 1.3.5.1. | Review; general SDH biology | Stoichiometry given in review; no strain-specific kinetic values | Bouillaud, 2023 | 02/2023 | https://doi.org/10.3390/ijms24044045 | (bouillaud2023inhibitionofsuccinate pages 3-5) |
| role/pathway | SDH/complex II links the TCA cycle and electron transport chain; SdhA is the catalytic flavoprotein subunit of this respiratory enzyme. | Review + primary; general bacteria | Not reported for KT2440 | Bouillaud, 2023; McNeil et al., 2012 | 02/2023; 05/2012 | https://doi.org/10.3390/ijms24044045 ; https://doi.org/10.1074/jbc.m111.293803 | (bouillaud2023inhibitionofsuccinate pages 3-5, mcneil2012sdheisa pages 1-2) |
| cofactors | Bacterial SdhA is a FAD-dependent flavoprotein; SDH contains FAD and iron cofactors, and SdhE is required for SdhA flavinylation in bacteria. | Review + primary; general bacteria | Loss of SdhE caused ~90% reduction in SDH activity in Serratia model | McNeil et al., 2012; Bouillaud, 2023 | 05/2012; 02/2023 | https://doi.org/10.1074/jbc.m111.293803 ; https://doi.org/10.3390/ijms24044045 | (mcneil2012sdheisa pages 4-5, bouillaud2023inhibitionofsuccinate pages 3-5, mcneil2012sdheisa pages 1-2) |
| complex subunits/operon | In KT2440, the SDH subunits are mapped as SdhB/PP_4190, SdhA/PP_4191, SdhD/PP_4192, and SdhC/PP_4193. This supports assignment of PP_4191 to the canonical bacterial SDH complex. | Primary; P. putida KT2440 | Not reported | Chavarría et al., 2012 | 05/2012 | https://doi.org/10.1128/mbio.00028-12 | (chavarria2012regulatorytasksof media b14b64f4, chavarria2012regulatorytasksof media 8dabbe7d) |
| localization | SDH is a membrane-spanning complex with a soluble catalytic side containing SdhA and membrane subunits that transfer electrons to quinone; bacterial experiments localized SdhA to the membrane-associated complex. | Review + primary; general bacteria | Functional SDH reported as ~360 kDa trimeric complex in Serratia model | Bouillaud, 2023; McNeil et al., 2012 | 02/2023; 05/2012 | https://doi.org/10.3390/ijms24044045 ; https://doi.org/10.1074/jbc.m111.293803 | (mcneil2012sdheisa pages 4-5, bouillaud2023inhibitionofsuccinate pages 3-5) |
| regulation/expression | In P. putida, sdhA expression decreases under microaerobic cultivation, consistent with reduced succinate oxidation when oxygen becomes limiting. | Primary; P. putida | ~2.2-fold reduction of sdhA expression in wild type under microaerobic vs aerobic conditions | Mutyala et al., 2023 | 07/2023 | https://doi.org/10.1021/acsomega.3c02520 | (mutyala2023citratesynthaseoverexpression pages 10-11) |
| phenotypes/essentiality | KT2440 transposon screening identified the succinate dehydrogenase complex (5 genes) among genes important for growth on minimal medium, supporting central metabolic importance, though not proving PP_4191 alone is universally essential. | Primary; P. putida KT2440 | Gene count only; no PP_4191-specific effect size in provided context | Molina-Henares et al., 2010 | 06/2010 | https://doi.org/10.1111/j.1462-2920.2010.02166.x | (chavarria2012regulatorytasksof pages 3-4) |
| applications/engineering relevance | Because KT2440 can reassimilate succinate using sdhAB, downregulating or deleting sdhAB is proposed to improve biotechnological succinate accumulation; microaerobic repression of sdhA supports this strategy. | Primary; P. putida | gltA overexpression improved succinate production by ~50%; succinate reached 4.73 ± 0.6 mM in 36 h, ~400% above wild type at pH 7.5; sdhA expression reduced ~2.2-fold microaerobically | Mutyala et al., 2023 | 07/2023 | https://doi.org/10.1021/acsomega.3c02520 | (mutyala2023citratesynthaseoverexpression pages 10-11) |
Table: This table summarizes evidence-supported functional annotation points for Pseudomonas putida KT2440 sdhA (PP_4191; UniProt Q88FA7), including identity, biochemistry, pathway role, localization, and engineering relevance. It only includes claims directly supported by the available evidence contexts.
References
(chavarria2012regulatorytasksof pages 3-4): Max Chavarría, Roelco J. Kleijn, Uwe Sauer, Katharina Pflüger-Grau, and Víctor de Lorenzo. Regulatory tasks of the phosphoenolpyruvate-phosphotransferase system of pseudomonas putida in central carbon metabolism. May 2012. URL: https://doi.org/10.1128/mbio.00028-12, doi:10.1128/mbio.00028-12. This article has 96 citations and is from a domain leading peer-reviewed journal.
(chavarria2012regulatorytasksof media b14b64f4): Max Chavarría, Roelco J. Kleijn, Uwe Sauer, Katharina Pflüger-Grau, and Víctor de Lorenzo. Regulatory tasks of the phosphoenolpyruvate-phosphotransferase system of pseudomonas putida in central carbon metabolism. May 2012. URL: https://doi.org/10.1128/mbio.00028-12, doi:10.1128/mbio.00028-12. This article has 96 citations and is from a domain leading peer-reviewed journal.
(chavarria2012regulatorytasksof media 8dabbe7d): Max Chavarría, Roelco J. Kleijn, Uwe Sauer, Katharina Pflüger-Grau, and Víctor de Lorenzo. Regulatory tasks of the phosphoenolpyruvate-phosphotransferase system of pseudomonas putida in central carbon metabolism. May 2012. URL: https://doi.org/10.1128/mbio.00028-12, doi:10.1128/mbio.00028-12. This article has 96 citations and is from a domain leading peer-reviewed journal.
(bouillaud2023inhibitionofsuccinate pages 3-5): Frederic Bouillaud. Inhibition of succinate dehydrogenase by pesticides (sdhis) and energy metabolism. International Journal of Molecular Sciences, 24:4045, Feb 2023. URL: https://doi.org/10.3390/ijms24044045, doi:10.3390/ijms24044045. This article has 60 citations.
(mcneil2012sdheisa pages 1-2): Matthew B. McNeil, James S. Clulow, Nabil M. Wilf, George P.C. Salmond, and Peter C. Fineran. Sdhe is a conserved protein required for flavinylation of succinate dehydrogenase in bacteria. Journal of Biological Chemistry, 287:18418-18428, May 2012. URL: https://doi.org/10.1074/jbc.m111.293803, doi:10.1074/jbc.m111.293803. This article has 86 citations and is from a domain leading peer-reviewed journal.
(mcneil2012sdheisa pages 4-5): Matthew B. McNeil, James S. Clulow, Nabil M. Wilf, George P.C. Salmond, and Peter C. Fineran. Sdhe is a conserved protein required for flavinylation of succinate dehydrogenase in bacteria. Journal of Biological Chemistry, 287:18418-18428, May 2012. URL: https://doi.org/10.1074/jbc.m111.293803, doi:10.1074/jbc.m111.293803. This article has 86 citations and is from a domain leading peer-reviewed journal.
(mutyala2023citratesynthaseoverexpression pages 10-11): Sakuntala Mutyala, Shuwei Li, Himanshu Khandelwal, Da Seul Kong, and Jung Rae Kim. Citrate synthase overexpression of pseudomonas putida increases succinate production from acetate in microaerobic cultivation. ACS Omega, 8:26231-26242, Jul 2023. URL: https://doi.org/10.1021/acsomega.3c02520, doi:10.1021/acsomega.3c02520. This article has 13 citations and is from a peer-reviewed journal.