Recombinant Shewanella sediminis Na (+)-translocating NADH-quinone reductase subunit D
Description
Introduction to Shewanella sediminis and Na(+)-translocating NADH-quinone Reductase
Shewanella sediminis is a psychrophilic (cold-loving), rod-shaped, Gram-negative bacterium isolated from marine sediment. It has gained scientific interest for its ability to degrade hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), making it environmentally significant for bioremediation . The bacterium was first isolated from Halifax Harbour sediment and was subsequently characterized as a novel species within the Shewanella genus .
Na(+)-translocating NADH-quinone reductase (NQR) is an integral membrane protein complex that serves as a primary respiratory enzyme in many marine and halophilic bacteria. This complex catalyzes the oxidation of NADH and the reduction of quinones, coupled with the electrogenic translocation of sodium ions across the cell membrane . This mechanism is essential for energy conservation in these organisms, especially those adapting to marine environments with high sodium concentrations .
Recombinant Protein Characteristics
Table 1: Specifications of Recombinant Shewanella sediminis Na(+)-translocating NADH-quinone Reductase Subunit D
| Parameter | Specification |
|---|---|
| UniProt ID | A8FYV9 |
| Gene Name | nqrD |
| Locus Tag | Ssed_3428 |
| Protein Length | 210 amino acids (Full length) |
| Expression System | E. coli |
| Tag | His-tag (N-terminal) |
| Form | Lyophilized powder |
| Purity | >90% (SDS-PAGE) |
| Storage Buffer | Tris/PBS-based buffer, 6% Trehalose, pH 8.0 |
| Recommended Storage | -20°C/-80°C, aliquoting necessary for multiple use |
The recombinant form of this protein is typically produced with an N-terminal histidine tag to facilitate purification through affinity chromatography . The His-tagged recombinant protein maintains the structural integrity essential for functional studies while allowing for efficient isolation from expression systems .
Role in Electron Transport Chain
The Na(+)-translocating NADH-quinone reductase complex represents a unique adaptation in marine bacteria, allowing them to utilize sodium ion gradients rather than proton gradients for energy conservation. This adaptation is particularly advantageous in high-salt environments where maintaining proton gradients may be energetically unfavorable .
In the respiratory chain of marine bacteria like Shewanella sediminis, the NQR complex catalyzes the oxidation of NADH and transfers the electrons to quinones in the membrane. This electron transfer is coupled to the translocation of sodium ions across the membrane, generating an electrochemical sodium gradient that can be utilized for ATP synthesis, solute transport, and flagellar rotation .
Subunit D specifically contributes to the formation of the transmembrane channel through which sodium ions are translocated. Its hydrophobic domains span the membrane, creating a pathway for sodium movement in response to electron transfer events occurring within the complex .
Na+ Dependency and Cold Adaptation
Shewanella sediminis, like other members of the Na(+)-requiring group of Shewanella species, has evolved to utilize sodium ions for various cellular processes. The Na(+)-translocating NADH-quinone reductase is a critical component of this adaptation, allowing the bacterium to thrive in marine environments with high sodium concentrations .
Additionally, as a psychrophilic organism, S. sediminis has adapted its proteins, including the NQR complex, to function efficiently at low temperatures. These adaptations typically involve modifications that increase protein flexibility and reduce the energy required for conformational changes at cold temperatures . The genomic analysis of S. sediminis revealed decreased G+C content and reduced levels of amino acids like alanine, proline, and arginine in its proteome, which contribute to increased protein structural flexibility at low temperatures .
Expression Systems and Methods
The recombinant production of Shewanella sediminis Na(+)-translocating NADH-quinone reductase subunit D typically utilizes Escherichia coli as the expression host . This heterologous expression system offers several advantages, including rapid growth, high protein yields, and well-established genetic manipulation techniques.
The protein is expressed as a fusion construct with an N-terminal histidine tag, which facilitates subsequent purification steps without significantly affecting the protein's structure or function . The expression is carefully controlled to ensure proper folding and to prevent the formation of inclusion bodies, which can be challenging when expressing membrane proteins.
Purification Protocols
Table 2: Purification Protocol for Recombinant Na(+)-translocating NADH-quinone Reductase Subunit D
| Step | Procedure | Notes |
|---|---|---|
| Cell Lysis | Mechanical disruption or detergent-based methods | Careful extraction to preserve membrane protein integrity |
| Affinity Chromatography | Ni-NTA or similar matrix for His-tag binding | Conducted under native conditions to maintain protein structure |
| Washing | Buffer containing low imidazole concentrations | Removes non-specifically bound proteins |
| Elution | Buffer with high imidazole concentration | Releases target protein from affinity matrix |
| Buffer Exchange | Dialysis or gel filtration | Removes imidazole and adjusts to storage buffer conditions |
| Quality Control | SDS-PAGE, mass spectrometry | Confirms purity and identity |
The purified protein is typically stored in a Tris/PBS-based buffer containing 6% trehalose at pH 8.0 to maintain stability during storage . For long-term preservation, the addition of glycerol (final concentration of 50%) and storage at -20°C or -80°C is recommended .
Relationship to Other NQR Complexes
In V. alginolyticus, the NQR complex consists of three subunits (α, β, and γ) with apparent molecular weights of 52, 46, and 32 kDa, respectively . The FAD-containing β-subunit reacts with NADH and reduces ubiquinone-1 through a one-electron transfer pathway . In contrast, the Shewanella NQR complex has evolved specific adaptations for cold marine environments, potentially affecting the electron transfer kinetics and efficiency at low temperatures .
Evolutionary Relationships
The Na(+)-translocating NADH-quinone reductase represents an important evolutionary adaptation for life in marine environments. This enzyme is widely distributed among marine and moderately halophilic bacteria, indicating its fundamental role in the bioenergetics of these organisms .
Interestingly, the NQR complex shows some similarity to the Rnf complex, another membrane-bound electron transport complex found in various bacteria . Both complexes couple electron transfer with ion translocation across the membrane, although they differ in their specific electron donors and acceptors .
Biotechnological Applications
The recombinant Shewanella sediminis Na(+)-translocating NADH-quinone reductase subunit D has several potential biotechnological applications:
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Bioremediation: Understanding the electron transport mechanisms in S. sediminis could enhance its application in the degradation of environmental pollutants like RDX .
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Biosensors: The Na(+)-dependent electron transport properties could be utilized in the development of biosensors for environmental monitoring.
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Bioenergy: The unique ion-translocating capabilities might be harnessed for bioelectrochemical systems or microbial fuel cells.
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Structural Biology Research: As a model membrane protein, it provides insights into protein structure-function relationships in challenging environments.
Future Research Directions
Several promising areas for future research on this protein include:
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Detailed Structural Analysis: Advanced techniques like cryo-electron microscopy could provide higher-resolution structural information about the entire NQR complex and the specific role of subunit D.
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Mutational Studies: Systematic mutation of key residues could elucidate the precise mechanisms of electron transfer and sodium translocation.
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Comparative Genomics: Expanded analysis across Shewanella species could reveal evolutionary adaptations of the NQR complex to different environments.
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Synthetic Biology Applications: Engineered versions of the protein might be developed for specific biotechnological applications in bioremediation or bioenergy.
Product Specs
Note: We will prioritize shipping the format currently in stock. However, if you require a specific format, please indicate your preference when placing the order. We will fulfill your request as best as possible.
Note: All our proteins are shipped with standard blue ice packs. If you require dry ice shipping, please inform us in advance, as additional fees will apply.
Generally, the shelf life of the liquid form is 6 months at -20°C/-80°C. The shelf life of the lyophilized form is 12 months at -20°C/-80°C.
Target Background
KEGG: sse:Ssed_3428
STRING: 425104.Ssed_3428
Q&A
What is the functional role of NqrD in Shewanella species?
NqrD functions as a subunit of the Na(+)-translocating NADH-quinone reductase complex, which plays a crucial role in bacterial respiratory electron transport chains. This complex couples the oxidation of NADH to the reduction of quinones while pumping sodium ions across the membrane, generating an electrochemical gradient used for energy production.
In Shewanella species, NADH dehydrogenases (including the Na(+)-NQR complex) have been identified as key components in electron transfer processes. Research has shown that these enzymes are essential for inward electron transfer in Shewanella oneidensis MR-1, a closely related species . This electron transfer capability is particularly important for microbial electrosynthesis applications, where bacteria can accept electrons from electrodes to drive cellular processes that produce target molecules .
What expression systems are optimal for producing recombinant Shewanella sediminis NqrD?
Based on available data, E. coli has been successfully used as an expression host for recombinant Shewanella NqrD proteins. For the related S. oneidensis NqrD, E. coli expression systems with N-terminal His-tagging have been demonstrated to be effective .
The optimal expression strategy includes:
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Using a pET-based or similar expression vector with a strong inducible promoter
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Including an N-terminal His-tag for purification purposes
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Optimizing codon usage for E. coli if necessary
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Controlling expression temperature (typically 16-25°C after induction) to promote proper folding
Importantly, research has shown that the accessibility of translation initiation sites is a critical factor affecting recombinant protein expression success. Analysis of 11,430 recombinant proteins has demonstrated that mRNA base-unpairing across the Boltzmann's ensemble significantly impacts expression levels .
What are the recommended conditions for reconstitution and storage of purified recombinant NqrD?
For optimal handling of recombinant Shewanella NqrD proteins, the following protocols are recommended based on established methods for similar proteins:
Reconstitution Protocol:
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Centrifuge the vial briefly before opening to bring contents to the bottom
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Reconstitute the lyophilized protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL
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Add glycerol to a final concentration of 5-50% (with 50% being optimal for long-term storage)
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Aliquot the solution to minimize freeze-thaw cycles
Storage Conditions:
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Store lyophilized powder at -20°C/-80°C upon receipt
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Store reconstituted aliquots at -20°C/-80°C for long-term storage
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Working aliquots can be stored at 4°C for up to one week
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Avoid repeated freeze-thaw cycles as they may affect protein stability and activity
Storage Buffer:
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Tris/PBS-based buffer containing 6% Trehalose, pH 8.0 has been successfully used for similar proteins
How does the structure of NqrD contribute to the electron transfer mechanism in the Na(+)-NQR complex?
While the specific crystal structure of Shewanella sediminis NqrD has not been determined yet, insights can be gained from related quinone oxidoreductases. Research on the NADPH-dependent QOR from Phytophthora capsici (PcQOR) has revealed important structural features of quinone-binding sites that may be applicable to understanding NqrD function .
In the PcQOR-NADPH complex, the quinone-binding pocket involves several key residues that redistribute the substrate through interactions with the side chains (R45, Q48, Y54, C147, T148) and the NADPH nicotinamide ring. Electron transfer occurs when the phenyl ring of quinone stacks against the nicotinamide ring .
For NqrD, which is part of a more complex Na(+)-NQR system, the mechanism likely involves:
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Interaction with other subunits of the complex
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Positioning of quinone substrates for optimal electron acceptance
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Coordination with sodium ion translocation across the membrane
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Conformational changes during the catalytic cycle
What are the key differences between NqrD proteins from different Shewanella species?
Comparative analysis of NqrD proteins from different Shewanella species reveals both conserved domains essential for function and species-specific variations. While specific comprehensive comparisons of NqrD across all Shewanella species are not available in the search results, general differences between Shewanella species have been documented.
For example, S. alga and S. putrefaciens exhibit differences in hemolytic activity, growth at different temperatures and salt concentrations, and metabolic capabilities such as acid production from various carbohydrates . These species-level differences may extend to variations in their respiratory complexes, including the Na(+)-NQR complex.
Potential differences in NqrD proteins across Shewanella species might include:
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Amino acid substitutions affecting substrate binding affinity
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Variations in transmembrane domain structure affecting ion translocation efficiency
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Differences in interaction surfaces with other subunits of the complex
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Species-specific post-translational modifications
A comprehensive sequence alignment and structural modeling study would be necessary to fully characterize these differences.
How can recombinant NqrD be used in microbial electrosynthesis research?
Recombinant NqrD can serve as a valuable tool in microbial electrosynthesis research, particularly in understanding electron transfer mechanisms in Shewanella species. Research at Michigan State University has demonstrated that NADH dehydrogenases, which include components of the Na(+)-NQR complex, are limiting factors in microbial electrosynthesis by Shewanella oneidensis .
Practical applications include:
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Overexpression studies: Creating Shewanella strains with upregulated NqrD to potentially enhance electron uptake from electrodes
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Structure-function analysis: Using site-directed mutagenesis of recombinant NqrD to identify critical residues for electron transfer
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Protein-electrode interaction studies: Utilizing purified recombinant NqrD to study direct interaction with electrode surfaces
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In vitro reconstitution: Combining recombinant NqrD with other subunits to reconstruct functional Na(+)-NQR complexes for detailed mechanistic studies
As Dr. Michaela TerAvest stated, "Future work to upregulate these essential electron transfer complexes could result in improved microbial electrosynthesis capability in Shewanella or other microbes, bringing the process closer to industrially-relevant production levels."
What methodologies are most effective for assessing the activity of recombinant NqrD?
Several methodologies can be employed to assess the activity of recombinant NqrD, both as an isolated protein and as part of the Na(+)-NQR complex:
Spectrophotometric Assays:
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NADH oxidation can be monitored by measuring the decrease in absorbance at 340 nm
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Quinone reduction can be monitored by measuring changes in absorbance at wavelengths specific to the quinone being used
Electrochemical Techniques:
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Cyclic voltammetry to detect electron transfer between the protein and electrodes
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Chronoamperometry to measure sustained electron transfer rates
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Protein film voltammetry for direct measurement of the protein's redox properties
Sodium Ion Transport Assays:
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Using fluorescent sodium indicators to measure changes in sodium concentration
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Membrane vesicle studies with radiolabeled sodium to quantify transport activity
Structural Analysis:
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Circular dichroism to confirm proper folding of the recombinant protein
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Limited proteolysis to assess structural integrity and domain organization
For comprehensive activity assessment, combining multiple methods is recommended to evaluate both electron transfer capabilities and ion transport functions.
How can expression levels of recombinant NqrD be optimized in E. coli systems?
Optimizing expression levels of recombinant NqrD requires addressing several factors that influence protein production in E. coli:
Translation Initiation Site Accessibility:
Research has shown that the accessibility of translation initiation sites is a critical determinant of successful recombinant protein expression. The TIsigner approach, which uses simulated annealing to modify up to the first nine codons of mRNAs with synonymous substitutions, can significantly improve expression levels .
Key optimization strategies include:
Implementing these strategies can help overcome the approximately 50% failure rate often seen in recombinant protein production .
What are the common challenges in purifying active recombinant NqrD and how can they be addressed?
Purification of active membrane proteins like NqrD presents several challenges that require specific strategies:
Common Challenges and Solutions:
| Challenge | Underlying Issue | Solution Strategy |
|---|---|---|
| Low solubility | Hydrophobic transmembrane domains | Use appropriate detergents (DDM, LDAO, or Triton X-100) at critical micelle concentration |
| Protein aggregation | Improper folding during expression | Lower expression temperature; consider refolding protocols from inclusion bodies |
| Loss of activity during purification | Disruption of native lipid environment | Include phospholipids during purification; consider styrene maleic acid lipid particles (SMALPs) |
| Co-purification of contaminants | Non-specific binding to affinity resin | Add low concentrations of imidazole in binding buffer; consider tandem purification approach |
| Oxidation of sensitive residues | Exposure to oxygen during purification | Include reducing agents (DTT, β-mercaptoethanol) in all buffers; work under nitrogen atmosphere if possible |
| Instability during storage | Loss of quaternary structure | Store with glycerol (20-50%); consider addition of stabilizing ligands |
For optimal results when purifying NqrD, a tailored protocol should be developed:
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Lyse cells in buffer containing appropriate detergents
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Perform immobilized metal affinity chromatography (IMAC) with the His-tagged protein
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Consider size exclusion chromatography as a secondary purification step
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Assess protein integrity using SDS-PAGE (>90% purity should be achievable)
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Verify activity through functional assays before experimental use
How can recombinant NqrD contribute to carbon capture technologies?
Research on Shewanella oneidensis has demonstrated its potential for microbial electrosynthesis, which could capture carbon dioxide emissions and produce useful materials . Recombinant NqrD can contribute to advancing this technology in several ways:
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Enhanced Electron Transfer Systems:
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Engineered NqrD variants could improve electron uptake from electrodes
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Optimization of the entire Na(+)-NQR complex could increase electron transfer efficiency
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Creation of hybrid systems incorporating NqrD with artificial electron conduits
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Bioelectrochemical System Design:
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Immobilized recombinant NqrD on electrodes could serve as electron transfer mediators
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Development of biomimetic catalysts based on NqrD structure and function
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Integration into scaled bioreactor systems for improved performance
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Metabolic Engineering Applications:
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Co-expression of optimized NqrD with carbon-fixing pathways
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Creating synthetic electron transfer chains to connect electrode oxidation/reduction to CO₂ fixation
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Development of sensor systems using NqrD to monitor electron flow in bioelectrochemical systems
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As demonstrated by Michigan State University researchers, NADH dehydrogenases (including components of the Na(+)-NQR complex) are limiting factors in microbial electrosynthesis . Strategic engineering of NqrD could help overcome these limitations, potentially leading to "improved microbial electrosynthesis capability in Shewanella or other microbes, bringing the process closer to industrially-relevant production levels."
What comparative insights can be gained from studying NqrD across different Shewanella species?
Comparative studies of NqrD across different Shewanella species can provide valuable insights into adaptation, function, and evolutionary relationships:
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Structure-Function Relationships:
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Identification of conserved residues essential for electron transfer
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Understanding how species-specific variations affect substrate specificity
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Correlation between NqrD sequence variations and ecological niches of different Shewanella species
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Evolutionary Adaptations:
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Analysis of how NqrD has evolved in species adapted to different environments (marine vs. freshwater; psychrophilic vs. mesophilic)
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Identification of selective pressures on respiratory complexes in different ecological contexts
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Horizontal gene transfer patterns for respiratory complex components
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Biotechnological Applications:
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Discovery of species with NqrD variants optimized for specific applications
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Identification of naturally occurring mutations that enhance electron transfer capabilities
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Development of chimeric NqrD proteins combining beneficial features from multiple species
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Physiological Implications:
These comparative studies could leverage techniques from genomics, structural biology, and biochemistry to build a comprehensive understanding of this important respiratory complex component across the Shewanella genus.
