Recombinant Koribacter versatilis NADH-quinone oxidoreductase subunit K 1 (nuoK1)

What is the basic structure of Koribacter versatilis NADH-quinone oxidoreductase subunit K 1?

The nuoK1 protein from Koribacter versatilis is a full-length protein consisting of 101 amino acids. Its amino acid sequence is: MAEIGTMHYLVVAAMLFIIGTVGVVTRRNVVVILMSIELILNAVNLNLVAFSRLYGLHGQVFSIFVMVDAAAEAAVGLGIVIAFFRNKETVNVDEVDLLKW . The recombinant form typically includes an N-terminal His tag when expressed in E. coli expression systems. As part of the NADH-quinone oxidoreductase complex (also known as NADH dehydrogenase I or NDH-1), this subunit contributes to the multi-polypeptide structure of the enzyme, which contains noncovalently bound FMN and iron-sulfur clusters as prosthetic groups .

What is the functional role of nuoK1 within the respiratory chain of Koribacter versatilis?

The nuoK1 protein functions as a component of the NADH-quinone oxidoreductase complex (NDH-1), which plays a crucial role in the bacterial respiratory chain. This complex belongs to the energy-coupling type of NADH dehydrogenases, contributing to proton translocation across the membrane and subsequent ATP synthesis . In Koribacter versatilis, this function is particularly important given the organism's role in soil environments where it must adapt to varying nutrient conditions. The NADH-ubiquinone-1 reductase activities associated with this complex are typically inhibited by rotenone, capsaicin, and dicyclohexylcarbodiimide, which serves as a distinguishing feature from NDH-2 type enzymes .

What are the optimal conditions for reconstituting and storing recombinant nuoK1 protein?

For optimal handling of recombinant nuoK1 protein:

• Reconstitution protocol: Before opening, briefly centrifuge the vial to bring contents to the bottom. Reconstitute the lyophilized protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL .

• Storage preparation: Add glycerol to a final concentration of 5-50% (recommended 50%) and aliquot for long-term storage .

• Storage conditions: Store at -20°C/-80°C upon receipt. Aliquoting is necessary for multiple use to avoid repeated freeze-thaw cycles, which can damage protein integrity .

• Working aliquots: Working aliquots can be stored at 4°C for up to one week .

• Buffer composition: The protein is supplied in a Tris/PBS-based buffer containing 6% Trehalose, pH 8.0 .

What expression systems are most effective for producing recombinant Koribacter versatilis nuoK1?

Based on the available data, E. coli has been successfully used as an expression host for recombinant Koribacter versatilis nuoK1 protein . The protein is typically produced with an N-terminal His tag to facilitate purification. When designing expression protocols, researchers should consider:

• Codon optimization: Since Koribacter versatilis has a different codon usage pattern than E. coli, codon optimization might improve expression yields.

• Temperature and induction conditions: These should be optimized for membrane protein expression, as nuoK1 is likely a membrane-associated protein given its role in the respiratory chain.

• Solubilization strategies: Appropriate detergents may be necessary for extracting the protein from membranes while maintaining its native conformation.

• Purification approach: Affinity chromatography using the His tag is typically efficient, followed by additional purification steps if higher purity is required.

How can the activity of nuoK1 be measured in experimental settings?

While specific activity assays for isolated nuoK1 are not detailed in the search results, NADH-quinone oxidoreductase activity can generally be assessed through:

• Spectrophotometric assays: Monitoring NADH oxidation at 340 nm in the presence of appropriate quinone acceptors (decrease in absorbance indicates activity).

• Oxygen consumption assays: Using oxygen electrodes to measure oxygen consumption rates when the complex is functioning in the respiratory chain.

• Inhibitor sensitivity tests: Assessing sensitivity to known NDH-1 inhibitors like rotenone, capsaicin, and dicyclohexylcarbodiimide can confirm the protein is functioning as part of the NDH-1 complex .

• Reconstitution experiments: Incorporating the purified protein into liposomes to measure proton translocation activities.

What is known about the membrane topology and structural integration of nuoK1 in the complete NADH-quinone oxidoreductase complex?

Based on its amino acid sequence (MAEIGTMHYLVVAAMLFIIGTVGVVTRRNVVVILMSIELILNAVNLNLVAFSRLYGLHGQVFSIFVMVDAAAEAAVGLGIVIAFFRNKETVNVDEVDLLKW) , nuoK1 appears to be a hydrophobic protein likely embedded in the membrane. Advanced structural studies such as cryo-electron microscopy or X-ray crystallography would be needed to determine its precise orientation and interactions within the complete NADH-quinone oxidoreductase complex. Researchers investigating this aspect should consider:

• Membrane domain prediction tools: To identify potential transmembrane regions in the sequence.

• Comparative modeling: Using structures of homologous subunits from better-characterized bacterial species.

• Cross-linking studies: To identify interaction partners within the complex.

• Site-directed mutagenesis: To determine functionally important residues for assembly or activity.

How does the ecological niche of Koribacter versatilis influence the evolution and function of its respiratory enzymes including nuoK1?

Koribacter versatilis was first identified in Australian pasture soil in 2003 and can account for up to 14% of soil bacterial communities despite its slow growth rate . This ecological context provides important insights for researchers studying its respiratory enzymes:

• Adaptation to soil environments: The high abundance of iron in soil is critical for Koribacter versatilis survival , suggesting that iron-containing respiratory enzymes like NADH-quinone oxidoreductase may have specialized adaptations.

• Carbon cycling role: Koribacter versatilis contributes significantly to carbon cycling through degradation of complex polymers and CO oxidation . Its respiratory enzymes likely enable metabolic flexibility to utilize various carbon sources available in soil.

• Growth rate considerations: The slow growth rate of Koribacter versatilis (taking up to a week for visible colonies) may reflect energy conservation strategies involving specialized respiratory chain components.

• Genomic context: With 5,650,368 nucleotides and 4,777 proteins , comparative genomic analysis could reveal unique features of respiratory genes and their regulation in this organism.

What potential role does nuoK1 play in the carbon monoxide oxidation capabilities of Koribacter versatilis?

Koribacter versatilis plays a significant role in regulating carbon monoxide output on Earth, with CO-oxidizing bacteria removing approximately 20% of total CO emitted to Earth's atmosphere . While the direct involvement of nuoK1 in CO oxidation is not specified in the available data, researchers could investigate:

• Electron transfer pathways: Whether electrons from CO oxidation feed into the respiratory chain through the NADH-quinone oxidoreductase complex.

• Regulatory connections: Potential co-regulation of nuoK1 with genes known to be involved in CO oxidation.

• Metabolic flexibility: How nuoK1 might contribute to the organism's ability to switch between different carbon sources, including CO.

• Comparative analysis: Differences in nuoK1 sequence or expression between Koribacter versatilis and non-CO-oxidizing bacteria.

What are the key considerations for ensuring proper folding and activity of recombinant nuoK1 in functional studies?

When working with recombinant nuoK1 for functional studies, researchers should consider:

• Expression conditions optimization:

  • Temperature, induction time, and inducer concentration should be carefully optimized

  • Lower temperatures (16-25°C) often favor proper folding of membrane proteins

• Solubilization strategy:

  • Selection of appropriate detergents that maintain protein structure

  • Screening of different detergents (e.g., DDM, LDAO, Triton X-100) for optimal extraction

• Reconstitution into membrane mimetics:

  • Liposomes with lipid compositions mimicking bacterial membranes

  • Nanodiscs for single-particle studies

  • Detergent micelles for solution-based assays

• Activity validation methods:

  • Spectroscopic assays to confirm proper folding

  • Functional assays to verify electron transfer capability

  • Inhibitor sensitivity to confirm expected pharmacological profile

How can researchers effectively address the challenges of heterologous expression of Koribacter versatilis proteins?

Heterologous expression of proteins from Koribacter versatilis presents unique challenges that can be addressed through:

• Host selection optimization:

  Expression Host	Advantages	Challenges
  E. coli	Well-established, fast growth	Potential codon bias, improper folding
  Pseudomonas species	Closer phylogenetic relation	Less developed genetic tools
  Cell-free systems	Avoids toxicity issues	Lower yields, higher cost

• Genetic optimization strategies:

  • Codon optimization for the selected expression host

  • Use of solubility-enhancing fusion partners (e.g., MBP, SUMO)

  • Signal sequence optimization for membrane targeting

  • Regulated expression systems to minimize toxicity

• Culture condition considerations:

  • Media composition including trace elements important for Acidobacteria

  • Temperature and pH adjustments mimicking natural conditions

  • Induction protocol optimization (concentration, timing, duration)

• Purification approach:

  • Multi-step purification strategy beyond initial affinity chromatography

  • Quality control through size-exclusion chromatography

  • Activity assays at each purification step to track functional protein

What analytical techniques are most informative for studying the structure-function relationship of nuoK1?

For comprehensive analysis of nuoK1 structure-function relationships, researchers should consider employing:

• Structural characterization methods:

  • Cryo-electron microscopy for membrane protein complexes

  • X-ray crystallography if crystals can be obtained

  • NMR for dynamic studies of specific domains

  • Hydrogen-deuterium exchange mass spectrometry for conformational analysis

• Functional mapping approaches:

  • Site-directed mutagenesis of conserved residues

  • Chimeric proteins with homologous subunits from other species

  • Truncation analysis to identify functional domains

  • Cross-linking coupled with mass spectrometry to identify interaction partners

• Biophysical interaction studies:

  • Isothermal titration calorimetry for binding energetics

  • Surface plasmon resonance for interaction kinetics

  • Microscale thermophoresis for detecting subtle conformational changes

  • FRET-based assays for conformational dynamics

• Computational approaches:

  • Molecular dynamics simulations in membrane environments

  • Quantum mechanical calculations for electron transfer pathways

  • Evolutionary coupling analysis to identify co-evolving residues

  • Homology modeling based on related structures

How might understanding nuoK1 contribute to broader knowledge of bacterial adaptation to soil environments?

Research on nuoK1 from Koribacter versatilis can provide insights into bacterial adaptation through:

• Energy metabolism adaptation: Understanding how the respiratory chain of Koribacter versatilis is optimized for soil environments with fluctuating nutrient availability and oxygen levels. Given that Koribacter versatilis accounts for up to 14% of soil bacterial communities despite its slow growth , its energy conservation mechanisms likely represent successful adaptive strategies.

• Metal dependency analysis: Investigating how the iron requirement of Koribacter versatilis relates to the structure and function of its respiratory complexes, including the iron-sulfur clusters in NADH-quinone oxidoreductase.

• Comparative genomics: Analyzing how the nuoK1 gene differs between Koribacter versatilis and bacteria from other environments, potentially revealing environment-specific adaptations in respiratory machinery.

• Carbon cycling contributions: Exploring how respiratory enzymes contribute to the organism's role in carbon cycling, particularly its ability to degrade complex polymers and oxidize CO .

What potential biotechnological applications might arise from research on Koribacter versatilis respiratory enzymes?

The unique properties of Koribacter versatilis and its respiratory enzymes could lead to several biotechnological applications:

• Bioremediation tools: Development of carbon monoxide mitigation technologies based on Koribacter versatilis enzymes, given its natural role in removing atmospheric CO .

• Biocatalysts for challenging reactions: Exploitation of the electron transport capabilities of modified respiratory enzymes for specific biotransformations.

• Soil health biomarkers: Using nuoK1 or related genes as biomarkers for monitoring soil ecosystem health and function.

• Bioenergy applications: Potential adaptation of efficient electron transport systems for microbial fuel cells or bioelectrochemical systems.

• Novel antibacterial targets: Understanding the unique features of Acidobacteria respiratory chains could reveal targets for environmentally-friendly antimicrobials for agricultural applications.

How does the presence of multiple NADH-quinone oxidoreductase types in a single bacterium impact metabolic flexibility and ecological fitness?

Some bacteria possess both NDH-1 and NDH-2 type NADH-quinone oxidoreductases in a single strain , which has significant implications for metabolism:

• Energy efficiency regulation: NDH-1 couples electron transfer to proton pumping (energy-conserving) while NDH-2 does not (energy-dissipating) . This dual system allows bacteria to balance energy conservation versus rapid electron flux depending on environmental conditions.

• Substrate adaptability: Different NADH-quinone oxidoreductase types may have different substrate preferences or regulatory mechanisms, expanding the range of metabolic substrates the organism can utilize.

• Oxygen response mechanisms: The balance between different respiratory enzyme types may shift in response to oxygen availability, allowing adaptation to microaerobic or fluctuating oxygen conditions common in soil environments.

• Stress response capacity: Alternative respiratory pathways provide redundancy that can be crucial during stress conditions, potentially explaining the ecological success of bacteria like Koribacter versatilis despite their slow growth rates .