Recombinant Ralstonia solanacearum NADH-quinone oxidoreductase subunit K (nuoK)
Product Specs
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Generally, the shelf life of liquid form is 6 months at -20°C/-80°C. The shelf life of lyophilized form is 12 months at -20°C/-80°C.
Target Background
KEGG: rso:RSc2052
STRING: 267608.RSc2052
Q&A
What is Ralstonia solanacearum NADH-quinone oxidoreductase subunit K (nuoK)?
NADH-quinone oxidoreductase subunit K (nuoK) is a membrane protein component of the respiratory chain complex I in Ralstonia solanacearum. It functions as part of the NADH dehydrogenase I complex (NDH-1) that catalyzes electron transfer from NADH to quinones in the bacterial inner membrane, contributing to energy generation through the respiratory chain. The protein is encoded by the nuoK gene (locus RSc2052 in the GMI1000 strain) and consists of 101 amino acids in its full-length form . The protein has a highly hydrophobic character, containing multiple transmembrane domains that anchor it within the bacterial membrane.
What are the structural characteristics of nuoK protein?
The nuoK protein is a small, hydrophobic membrane protein with several key structural features:
The highly hydrophobic nature of this protein, as evidenced by the abundance of hydrophobic amino acids (leucine, isoleucine, valine, etc.) in its sequence, suggests multiple membrane-spanning domains that are critical for its integration into the bacterial membrane and function within the respiratory complex.
How does nuoK contribute to bacterial metabolism?
The nuoK subunit plays a critical role in the energy metabolism of Ralstonia solanacearum by participating in the electron transport chain. As part of the NADH-quinone oxidoreductase complex (Complex I), it helps catalyze the transfer of electrons from NADH to quinones, coupled with proton translocation across the membrane. This process contributes to the generation of the proton motive force that drives ATP synthesis, providing the bacterium with the energy needed for various cellular processes, including pathogenesis and survival within host plants . The protein's membrane localization is essential for maintaining the structural integrity of the respiratory complex and facilitating efficient electron transfer.
What expression systems are optimal for producing recombinant nuoK?
Based on available research data, E. coli has been successfully employed as an expression system for recombinant nuoK protein production:
When expressing membrane proteins like nuoK, researchers should consider using specialized E. coli strains designed for membrane protein expression or alternative systems such as yeast or insect cells if functional studies requiring proper folding are planned. The selection of an N-terminal His-tag has proven effective for purification while minimizing interference with protein function .
What are the recommended storage and handling conditions for recombinant nuoK?
Proper storage and handling of recombinant nuoK is critical for maintaining protein stability and activity:
It is advisable to centrifuge vials briefly before opening to ensure all material is at the bottom of the tube. When working with membrane proteins like nuoK, additional considerations may include the addition of mild detergents to maintain solubility or reconstitution into lipid vesicles for functional studies .
What purification strategies are most effective for recombinant nuoK?
For His-tagged recombinant nuoK, the following purification strategy has proven effective:
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Immobilized Metal Affinity Chromatography (IMAC): Using Ni-NTA or similar matrices to capture the His-tagged protein directly from cell lysates.
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Detergent selection: Careful selection of detergents (such as DDM, LDAO, or Fos-choline) is critical for membrane protein solubilization while maintaining structural integrity.
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Size Exclusion Chromatography (SEC): As a polishing step to remove aggregates and ensure homogeneity.
The target purity level should exceed 90% as determined by SDS-PAGE analysis , which is suitable for most research applications including structural studies and functional assays.
How might nuoK function relate to Ralstonia solanacearum pathogenicity?
Ralstonia solanacearum is a widespread bacterial plant pathogen causing bacterial wilt in numerous plant species, including economically important crops . The connection between nuoK function and pathogenicity may involve several aspects:
Research into the role of respiratory chain components in bacterial pathogens suggests that disruption of energy metabolism can significantly impact virulence. The nuoK subunit, as part of the respiratory complex I, may therefore represent a potential target for controlling R. solanacearum infections in agricultural settings .
What analytical techniques are most informative for studying nuoK structure-function relationships?
Several advanced techniques can provide valuable insights into nuoK structure-function relationships:
| Technique | Application | Information Obtained |
|---|---|---|
| Cryo-electron microscopy | Structural analysis | High-resolution structural data of nuoK within the respiratory complex |
| Site-directed mutagenesis | Functional analysis | Identification of critical residues for function and interactions |
| Isothermal titration calorimetry | Binding studies | Thermodynamic parameters of nuoK interactions with other complex components |
| Blue native PAGE | Complex assembly | Assessment of nuoK incorporation into the respiratory complex |
| Membrane potential assays | Functional analysis | Evaluation of respiratory complex activity with modified nuoK variants |
| Molecular dynamics simulations | Theoretical analysis | Insights into dynamic aspects of nuoK within the membrane environment |
Combining these approaches in a comprehensive research program can provide a detailed understanding of how nuoK structure relates to its function within the respiratory complex and potentially its role in bacterial pathogenicity.
How can comparative genomic analyses of nuoK inform evolutionary studies of Ralstonia solanacearum?
Comparative genomic analyses of nuoK sequences across Ralstonia solanacearum strains can provide valuable insights into bacterial evolution and adaptation:
| Analysis Approach | Research Question | Potential Outcome |
|---|---|---|
| Phylogenetic analysis | How has nuoK evolved across R. solanacearum phylotypes? | Identification of selection pressures on respiratory components |
| Sequence conservation | Which regions of nuoK are most conserved? | Determination of functionally critical domains |
| Strain comparison | Do nuoK sequences differ between strains with varying host ranges? | Correlation between nuoK variants and host specificity |
| Horizontal gene transfer | Has nuoK been subject to horizontal transfer events? | Understanding the evolution of respiratory complexes in plant pathogens |
Ralstonia solanacearum is described as a highly flexible organism capable of rapid adaptation to environmental changes and new hosts . Studying the evolution of essential metabolic components like nuoK can provide insights into how this pathogen has adapted to diverse ecological niches and host plants.
What are common challenges when working with recombinant nuoK and how can they be addressed?
Researchers working with recombinant nuoK may encounter several challenges due to its nature as a membrane protein:
| Challenge | Cause | Solution |
|---|---|---|
| Low expression levels | Toxicity to host cells | Use tightly controlled inducible expression systems; lower induction temperature |
| Protein aggregation | Improper folding in expression host | Optimize detergent selection; consider fusion partners to enhance solubility |
| Loss of activity during purification | Harsh purification conditions | Use milder detergents; maintain cold temperatures throughout purification |
| Inconsistent reconstitution | Variable lipid incorporation | Standardize lipid composition and protein-to-lipid ratios; validate incorporation |
| Poor antibody recognition | Conformational epitopes disrupted | Use multiple detection antibodies targeting different regions; consider native PAGE |
| Degradation during storage | Protease contamination | Add protease inhibitors; ensure high purity before storage |
When troubleshooting expression and purification issues, it's advisable to analyze samples at each step of the procedure using techniques such as Western blotting, ELISA, or activity assays to identify at which point problems are occurring.
How can researchers validate the functional integrity of purified recombinant nuoK?
Validating the functional integrity of recombinant nuoK is essential before using it in downstream applications:
| Validation Method | Principle | Interpretation |
|---|---|---|
| NADH oxidation assay | Measures electron transfer from NADH to artificial electron acceptors | Active protein should catalyze NADH oxidation when incorporated into proteoliposomes |
| Proton pumping assay | Measures pH changes across membranes containing reconstituted protein | Functional nuoK will contribute to proton translocation when part of the complex |
| Binding assays | Assesses interaction with known complex I components | Properly folded nuoK should maintain its ability to interact with partner proteins |
| Circular dichroism (CD) | Evaluates secondary structure content | Spectrum should be consistent with membrane protein with predicted α-helical content |
| Thermal shift assay | Determines protein stability | Stable, properly folded protein will show cooperative unfolding |
It's important to note that as nuoK functions as part of a multi-subunit complex, some functional assays may require co-expression or reconstitution with other complex I components to obtain meaningful results.
How should researchers approach contradictory results in nuoK studies?
When faced with contradictory results in nuoK research, a systematic approach is recommended:
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Experimental design reassessment:
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Evaluate if differences in experimental conditions could explain contradictory results
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Consider variables such as expression systems, tags, purification methods, and assay conditions
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Technical validation:
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Verify protein identity by mass spectrometry
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Confirm purity by multiple methods (SDS-PAGE, SEC-MALS)
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Assess protein state (monomer vs. oligomer, native vs. denatured)
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Biological context:
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Consider strain-specific differences in nuoK sequence or function
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Evaluate the impact of the experimental system on protein behavior
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Assess whether in vitro conditions adequately represent the in vivo environment
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Collaborative verification:
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Engage with other laboratories to independently reproduce critical experiments
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Consider using complementary methodologies to address the same question
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Computational analysis:
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Use molecular modeling to predict the impact of experimental conditions
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Perform literature meta-analysis to identify patterns in contradictory results
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Contradictory results often reveal important nuances in protein behavior that can lead to deeper understanding of nuoK function in different contexts.
What emerging technologies show promise for advancing nuoK research?
Several cutting-edge technologies hold significant potential for advancing our understanding of nuoK:
| Technology | Application to nuoK Research | Potential Impact |
|---|---|---|
| Cryo-EM | High-resolution structural determination of nuoK within the respiratory complex | Detailed understanding of molecular interactions and mechanism |
| Single-molecule techniques | Dynamics of nuoK within the membrane environment | Insights into conformational changes during function |
| CRISPR-Cas9 genome editing | Precise manipulation of nuoK in native Ralstonia solanacearum | Direct correlation between nuoK variants and bacterial phenotypes |
| Hydrogen-deuterium exchange MS | Mapping dynamic protein-protein interactions | Understanding nuoK's role in complex assembly and function |
| Computational protein design | Engineering improved or altered nuoK functions | Development of tools for studying respiratory chain function |
| Nanodiscs technology | Stable incorporation of nuoK into defined membrane environments | Improved functional studies in near-native conditions |
These technologies could help resolve current knowledge gaps regarding how nuoK contributes to respiratory complex function and potentially to bacterial pathogenicity.
How might nuoK research contribute to understanding and controlling Ralstonia solanacearum infections?
Research on nuoK may provide valuable insights for agricultural applications:
| Research Area | Potential Contribution | Agricultural Impact |
|---|---|---|
| Energy metabolism inhibitors | Identification of compounds that specifically target bacterial respiratory complexes | Novel bactericides with specific activity against plant pathogens |
| Virulence-metabolism connections | Understanding how energy production relates to virulence factor expression | Strategies to attenuate bacterial pathogenicity |
| Host-pathogen interactions | Insights into bacterial adaptation to host environments | Development of plant varieties with enhanced resistance |
| Bacterial physiology | Understanding of persistence mechanisms under stress conditions | Improved management strategies for infected fields |
| Diagnostic development | Identification of specific markers related to respiratory function | Early detection methods for Ralstonia infections |
As Ralstonia solanacearum is a soil-borne bacterium causing widespread disease in economically important crops , advances in understanding its basic biology through nuoK research could contribute significantly to developing sustainable control strategies.
