Recombinant Nitratiruptor sp. Succinyl-CoA ligase [ADP-forming] subunit beta (sucC)

What is Nitratiruptor sp. Succinyl-CoA ligase [ADP-forming] subunit beta (sucC)?

Nitratiruptor sp. Succinyl-CoA ligase [ADP-forming] subunit beta (sucC) is a key enzyme subunit found in the extremophilic bacterium Nitratiruptor sp. strain SB155-2, which was isolated from hydrothermal vent ecosystems. This protein is part of the Succinyl-CoA ligase complex that catalyzes the reversible conversion of succinyl-CoA to succinate in the tricarboxylic acid (TCA) cycle, coupling this reaction with the formation of ADP from AMP and phosphate . The recombinant form has a UniProt accession number A6Q391 and consists of a specific amino acid sequence that determines its structure and function . Nitratiruptor sp. is classified among denitrifying epsilonproteobacteria found in hydrothermal environments, specifically from in situ samplers deployed on actively venting sulfide mounds .

How does Nitratiruptor sp. differ from other bacteria in hydrothermal vent ecosystems?

Nitratiruptor sp. belongs to a group of denitrifying epsilonproteobacteria that play crucial roles in hydrothermal vent ecosystems. Unlike many other bacteria found in these environments, Nitratiruptor possesses specific metabolic adaptations, including unique denitrification pathways. While many epsilonproteobacteria in these environments (like Sulfurimonas, Sulfurovum, and Nitratifractor) have nirS genes with little similarity to other nirS genes in public databases, Nitratiruptor is notable because its nirS sequence can be captured using standard primer sets, unlike its relatives . This genetic distinction suggests a potentially different evolutionary history or functional adaptation. Nitratiruptor sp. strain SB155-2 was specifically isolated from in situ samplers on an actively venting sulfide mound, indicating its adaptation to extreme temperature and chemical conditions .

How does the function of sucC in Nitratiruptor sp. compare to homologs in other species?

While the specific functional differences between Nitratiruptor sp. sucC and its homologs in other species are not extensively documented in the provided search results, we can draw some informed comparisons based on the available data.

In eukaryotes like humans, the homologous SUCLA2 (Succinyl-CoA ligase ADP-forming subunit beta) has been extensively studied. Research indicates that SUCLA2 can have functions beyond its canonical role in the TCA cycle. For instance, in cancer cells, SUCLA2 has been shown to relocate from mitochondria to the cytosol upon cell detachment, where it binds to and promotes the formation of stress granules . This non-canonical function facilitates protein translation of antioxidant enzymes including catalase, which helps mitigate oxidative stress and contributes to cancer metastasis .

The sucC protein from Nitratiruptor sp., being from an extremophilic bacterium that lives in hydrothermal vent environments, likely has structural adaptations that enable it to function under high temperatures and pressures. These adaptations might include increased thermostability, different pH optima, or altered substrate affinities compared to mesophilic homologs. Additionally, given Nitratiruptor's role in denitrification processes , its metabolic context may influence how sucC integrates with other metabolic pathways compared to organisms that don't perform denitrification.

What expression systems are most effective for producing recombinant Nitratiruptor sp. sucC?

Based on the available information, recombinant Nitratiruptor sp. sucC has been successfully expressed in yeast expression systems . This approach likely takes advantage of yeast's eukaryotic protein processing capabilities while allowing for higher protein yields than bacterial systems for certain proteins.

For researchers working with this protein, several considerations should guide the choice of expression system:

What are the recommended methods for assessing the enzymatic activity of recombinant Nitratiruptor sp. sucC?

Enzymatic activity of Succinyl-CoA ligase can be assessed through several methodological approaches:

• Coupled enzyme assays: The ADP produced during the reaction can be coupled to pyruvate kinase and lactate dehydrogenase reactions, allowing spectrophotometric monitoring of NADH oxidation at 340 nm.

• Direct measurement of CoA release: The release of CoA during the forward reaction can be monitored using thiol-reactive compounds like DTNB (5,5'-dithiobis-(2-nitrobenzoic acid)).

• Isotopic labeling studies: Using isotopically labeled substrates (e.g., 13C-labeled succinate) can help track the reaction progress and product formation.

• Thermal activity profiling: Given the extremophilic nature of Nitratiruptor sp., assessing activity across a range of temperatures (particularly at elevated temperatures) would be informative for understanding its thermal adaptations.

• pH dependency studies: Testing activity across various pH conditions can reveal optimal conditions and provide insights into the protein's adaptation to the hydrothermal vent environment.

Researchers should establish standard reaction conditions that reflect the native environment of Nitratiruptor sp., potentially including higher temperatures and pressures than typically used for mesophilic enzymes.

How can protein-protein interaction studies identify sucC binding partners in Nitratiruptor sp.?

To investigate protein-protein interactions involving Nitratiruptor sp. sucC, researchers can employ several complementary approaches:

• Co-immunoprecipitation (Co-IP): Using antibodies against sucC to pull down protein complexes, followed by mass spectrometry to identify binding partners.

• Bacterial two-hybrid systems: These can be used to screen for potential interacting proteins in a relatively high-throughput manner.

• Pull-down assays with purified proteins: Using tagged recombinant sucC as bait to identify interacting proteins from Nitratiruptor sp. lysates.

• Cross-linking studies: Chemical cross-linking combined with mass spectrometry can capture and identify transient protein-protein interactions.

• Surface plasmon resonance (SPR): For quantitative analysis of binding kinetics between sucC and candidate interacting proteins.

Based on findings from homologous proteins, potential interacting partners might include:

• The alpha subunit of the Succinyl-CoA ligase complex

• Other TCA cycle enzymes

• Components of stress granules (as seen with human SUCLA2)

• Proteins involved in denitrification pathways specific to Nitratiruptor sp.

How does the environmental context of hydrothermal vents influence sucC function in Nitratiruptor sp.?

Nitratiruptor sp. has been isolated from hydrothermal vent chimneys and actively venting sulfide mounds , environments characterized by extreme conditions including high temperatures, high pressures, steep chemical gradients, and often low oxygen levels. These conditions likely influence sucC function in several ways:

• Temperature adaptation: The sucC protein likely possesses thermostable properties that allow it to maintain structural integrity and catalytic activity at elevated temperatures characteristic of hydrothermal vents.

• Pressure effects on catalysis: High hydrostatic pressures can affect enzyme kinetics and protein conformational states, potentially influencing the catalytic efficiency of sucC.

• Metabolic context of denitrification: Nitratiruptor sp. is a denitrifying bacterium , suggesting that sucC functions within a metabolic network that includes nitrogen metabolism. The TCA cycle intermediates may serve as carbon skeletons for amino acid synthesis or other biosynthetic pathways linked to denitrification.

• Redox considerations: Hydrothermal vent environments often feature variable and extreme redox conditions. The function of sucC may be adapted to these conditions, potentially with mechanisms to maintain activity despite fluctuating redox states.

• Metal ion dependencies: The extreme environment may influence the availability of metal ions that could serve as cofactors for sucC activity, potentially leading to adaptations in metal binding or utilization.

What potential non-canonical functions might Nitratiruptor sp. sucC have outside the TCA cycle?

Studies on homologous proteins suggest potential non-canonical functions for Nitratiruptor sp. sucC. Research on human SUCLA2 has revealed that this protein can translocate from mitochondria to the cytosol under certain conditions (specifically during cell detachment) and interact with stress granules . These interactions promote the formation of stress granules that facilitate protein translation of antioxidant enzymes, contributing to cellular survival under stress conditions .

By analogy, Nitratiruptor sp. sucC might similarly possess functions beyond its canonical role in the TCA cycle, particularly given the extreme and variable conditions of its native environment. Potential non-canonical functions could include:

• Stress response mechanisms: Similar to SUCLA2, sucC might participate in stress response pathways specific to extremophilic conditions.

• Protein-RNA interactions: The interaction with stress granules observed in SUCLA2 suggests potential RNA-binding capabilities that might extend to Nitratiruptor sp. sucC.

• Redox regulation: The connection between SUCLA2 and antioxidant enzyme expression suggests a potential role in redox homeostasis, which could be particularly relevant in the variable redox conditions of hydrothermal vents.

• Metabolic flexibility: SucC might participate in alternative metabolic pathways that become important under specific environmental stresses or nutrient limitations.

How do the denitrification pathways in Nitratiruptor sp. potentially interact with sucC function?

Nitratiruptor sp. is classified among denitrifying epsilonproteobacteria found in hydrothermal vent ecosystems . The denitrification process involves the reduction of nitrates to nitrogen gas through several intermediate steps, requiring specific enzymes and energy. The relationship between denitrification and sucC function could involve several aspects:

• Energy coupling: The ADP-forming activity of Succinyl-CoA ligase generates a high-energy phosphate bond, potentially providing energy for the energy-demanding denitrification process.

• Carbon flux regulation: The TCA cycle, in which sucC participates, provides carbon skeletons and reducing equivalents that may support denitrification reactions.

• Transcriptional co-regulation: The genes for sucC and denitrification enzymes might be co-regulated in response to environmental conditions, such as oxygen availability or nitrogen compound concentrations.

• Enzyme complex formation: SucC might physically interact with components of the denitrification machinery in multienzyme complexes that facilitate metabolic channeling.

Nitratiruptor contains nirS genes that encode nitrite reductase, a key enzyme in denitrification . Unlike some related genera where nirS genes have low similarity to common database sequences, Nitratiruptor's nirS sequence can be captured using standard primer sets , suggesting potential differences in how its denitrification pathways have evolved and how they might interact with central metabolism involving sucC.

What are common challenges in working with recombinant Nitratiruptor sp. sucC and how can they be addressed?

Researchers working with recombinant Nitratiruptor sp. sucC may encounter several challenges:

• Protein solubility and folding: As an enzyme from an extremophile, sucC may fold incorrectly or form inclusion bodies when expressed in mesophilic hosts.

  • Solution: Test expression at lower temperatures, use solubility-enhancing fusion tags (e.g., MBP, SUMO), or employ refolding protocols from inclusion bodies.

• Enzyme instability under standard laboratory conditions: The protein may be adapted to extreme conditions of hydrothermal vents.

  • Solution: Optimize buffer conditions (pH, salt concentration), include stabilizing agents like glycerol or specific metal ions, and consider performing assays at elevated temperatures.

• Low enzymatic activity: Activity might be suboptimal when assayed under standard conditions.

  • Solution: Test activity across ranges of temperature, pH, and pressure; ensure all necessary cofactors are present; and consider the presence of potential inhibitors in reaction buffers.

• Lack of appropriate antibodies: Commercial antibodies for this specific protein may be unavailable.

  • Solution: Generate custom antibodies, use epitope tagging approaches, or detect activity rather than protein directly.

• Contaminating activities: Expression hosts may contain endogenous Succinyl-CoA ligase activity that interferes with assays.

  • Solution: Use appropriate negative controls, specific inhibitors, or genetic knockout expression hosts.

What considerations are important when designing site-directed mutagenesis studies for Nitratiruptor sp. sucC?

Site-directed mutagenesis is a powerful approach for investigating structure-function relationships in enzymes like sucC. Key considerations include:

How can researchers distinguish between the canonical TCA cycle function and potential non-canonical functions of Nitratiruptor sp. sucC?

Distinguishing between canonical and non-canonical functions of sucC requires experimental approaches that can separate these different roles. Based on studies of the homologous SUCLA2 protein , several strategies can be applied:

• Subcellular localization studies:

  • Track the localization of fluorescently tagged sucC under different environmental conditions

  • Use subcellular fractionation followed by Western blotting or activity assays

  • Compare with the localization of other Succinyl-CoA ligase subunits

• Separation of enzymatic and non-enzymatic functions:

  • Generate catalytically inactive mutants (by mutating key active site residues) and test for retention of non-canonical functions

  • Create truncation mutants to identify domains required for different functions

  • Use domain swapping with homologs to identify regions responsible for specific functions

• Interactome analysis:

  • Compare protein interaction partners under conditions that favor canonical versus potential non-canonical functions

  • Use proximity labeling approaches (BioID, APEX) to identify condition-specific interactors

  • Perform RNA immunoprecipitation to identify potential RNA interactions (as suggested by stress granule association of SUCLA2)

• Metabolic bypassing:

  • Supplement with cell-permeable metabolites (e.g., succinate) to bypass the need for canonical enzymatic activity

  • Use genetic approaches to complement TCA cycle function while testing for retention of other functions

• Comparative studies across species:

  • Compare with sucC homologs from non-extremophilic bacteria to identify functions specific to the Nitratiruptor sp. version

  • Study structure-function relationships across evolutionary diverse homologs

The human SUCLA2 studies demonstrated that its role in stress granule formation and regulation of antioxidant enzyme expression was independent of its TCA cycle function, as evidenced by the fact that other SCS complex components (SUCLG1, SUCLG2) did not show the same effect, and supplementation with cell-permeable succinate did not rescue the phenotype of SUCLA2 knockdown .