Recombinant Roseiflexus castenholzii NADH-quinone oxidoreductase subunit A (nuoA)
Description
Introduction to Roseiflexus castenholzii NADH-quinone oxidoreductase subunit A
NADH-quinone oxidoreductase subunit A (nuoA) is a critical component of the NADH dehydrogenase complex (Complex I) in the respiratory chain of Roseiflexus castenholzii. This bacterium represents a significant organism in evolutionary studies, as it forms the deepest branch of photosynthetic bacteria and is classified as a chlorosome-less filamentous anoxygenic phototroph . The nuoA protein functions as part of the NADH dehydrogenase I complex that catalyzes the transfer of electrons from NADH to quinones in the respiratory chain, contributing to the organism's energy production mechanisms.
The recombinant version of this protein is produced through genetic engineering techniques, typically involving expression in Escherichia coli, allowing for detailed study of its properties and functions outside of its native environment. The availability of this recombinant protein enables researchers to investigate its structural features, enzymatic activities, and potential applications in various biotechnological and research contexts.
Physicochemical Properties
The nuoA protein contains multiple hydrophobic amino acid residues, which is characteristic of membrane-associated proteins. This hydrophobicity profile allows the protein to integrate into the bacterial membrane where it performs its electron transfer functions. The predominance of alanine, valine, leucine, and glycine residues further supports its membrane-associated nature, as these amino acids are commonly found in transmembrane domains .
Expression System
The recombinant Roseiflexus castenholzii NADH-quinone oxidoreductase subunit A is produced using Escherichia coli as an expression host. This bacterial expression system provides several advantages, including high protein yields, relatively simple growth requirements, and established protocols for induction and purification .
The expression process typically involves cloning the nuoA gene into a suitable expression vector containing a histidine tag sequence and appropriate promoter. After transformation into E. coli host cells, protein expression is induced, followed by cell harvesting and protein purification.
Purification and Quality Control
The purification of recombinant nuoA protein typically employs affinity chromatography, taking advantage of the N-terminal His-tag that binds specifically to nickel or cobalt resins. This allows for selective retention of the target protein while contaminants are washed away. Additional purification steps may include size exclusion chromatography or ion exchange chromatography to achieve higher purity.
Quality control measures include SDS-PAGE analysis to confirm protein size and purity, which typically exceeds 90% for commercial preparations . Other quality control procedures may include mass spectrometry to verify the protein sequence and western blotting to confirm protein identity.
Enzymatic Function
The NADH-quinone oxidoreductase complex, of which nuoA is a subunit, plays a critical role in cellular respiration and energy metabolism. This complex (also known as Complex I) catalyzes the transfer of electrons from NADH to quinones, coupled with proton translocation across the membrane, contributing to the generation of a proton motive force used for ATP synthesis .
Although the search results don't provide specific details about the individual function of the nuoA subunit in Roseiflexus castenholzii, studies on homologous proteins in other bacteria suggest that nuoA likely contributes to the membrane anchor domain of the NADH-quinone oxidoreductase complex. This domain is crucial for embedding the complex in the bacterial membrane and may participate in forming the proton translocation pathway.
Role in Bacterial Energy Metabolism
In Roseiflexus castenholzii, which is an anoxygenic phototroph, the NADH-quinone oxidoreductase complex likely participates in both respiratory and photosynthetic electron transport chains. The integration of these energy-generating pathways is essential for the organism's survival in various environmental conditions.
The complex facilitates the electron transfer from NADH to the quinone pool, which can then distribute these reducing equivalents to different terminal electron acceptors depending on environmental conditions and energy demands. This flexibility in electron transport pathways contributes to the metabolic versatility of Roseiflexus castenholzii.
Evolutionary Studies
As Roseiflexus castenholzii represents one of the deepest branches of photosynthetic bacteria, studying its proteins, including nuoA, provides valuable insights into the evolution of photosynthesis and respiration . The nuoA protein sequence and structure can be compared with homologs from other organisms to trace evolutionary relationships and understand the adaptation of respiratory complexes across different bacterial lineages.
Biotechnological Applications
Understanding the structure and function of respiratory chain components like nuoA may inspire biotechnological applications, including the development of biocatalysts for specific redox reactions or the design of inhibitors targeting bacterial respiratory chains for antimicrobial purposes.
Product Specs
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Target Background
KEGG: rca:Rcas_2088
STRING: 383372.Rcas_2088
Q&A
What is NADH-quinone oxidoreductase subunit A (nuoA) and what is its significance in Roseiflexus castenholzii?
NADH-quinone oxidoreductase subunit A (nuoA) is an integral membrane protein component of Complex I (NADH dehydrogenase) in the electron transport chain of Roseiflexus castenholzii. This protein, also known as NDH-1 subunit A or NUO1, plays a crucial role in the initial steps of electron transfer during energy metabolism.
R. castenholzii is a chlorosome-less filamentous anoxygenic photosynthetic bacterium that represents one of the deepest branches of photosynthetic bacteria in evolutionary history . The organism contains a distinctive reaction center-light harvesting (RC-LH) complex that structurally resembles RC-LH1 but has spectroscopic characteristics similar to the peripheral LH2 of purple bacteria .
NuoA functions in the membrane domain of Complex I, participating in proton translocation across the membrane, which contributes to establishing the proton gradient necessary for ATP synthesis. The protein consists of 118 amino acids and contains a transmembrane domain that anchors it within the bacterial membrane .
What is the amino acid sequence and structural characteristics of Roseiflexus castenholzii nuoA?
The full amino acid sequence of Roseiflexus castenholzii nuoA (UniProt ID: A7NL04) is:
MLADYAFIGVFFIGAVIFPLVPLVAAYFLGPKRPTPIKLDTYECGLEAVGDIRVQFKIQYYLYALAFVIFDIEVVFLYPWAVAYGQIGLFALIAMAIFLVILVGGLVYEWKKGALEWV
The protein consists of 118 amino acids and appears to be predominantly hydrophobic, consistent with its role as a membrane protein component. Structural predictions suggest that nuoA contains transmembrane helices that span the cytoplasmic membrane.
The hydrophobic nature of the sequence, particularly the stretches of residues like IGVFFIGAVIFPLVPLVAAY and LYALAFVIFDIEVVFLYPWAVAY, is characteristic of transmembrane domains that anchor the protein within the lipid bilayer. The presence of charged residues such as lysine (K) and arginine (R) at positions likely to be exposed to the cytoplasm is consistent with the positive-inside rule for membrane protein topology.
How can recombinant Roseiflexus castenholzii nuoA be expressed and stored for research purposes?
Recombinant Roseiflexus castenholzii nuoA can be successfully expressed in E. coli expression systems with an N-terminal His-tag to facilitate purification . The expression construct typically includes the full-length protein (amino acids 1-118). Key considerations for expression and storage include:
Expression System:
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E. coli is the preferred heterologous expression system for nuoA
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Expression vectors incorporating N-terminal His-tags facilitate downstream purification
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Induction conditions should be optimized to balance protein yield with proper folding
Purification and Storage:
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After purification, the protein is typically prepared as a lyophilized powder
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The recommended storage buffer is Tris/PBS-based buffer with 6% trehalose at pH 8.0
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For reconstitution, deionized sterile water should be used to achieve a concentration of 0.1-1.0 mg/mL
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Addition of 5-50% glycerol (final concentration) is recommended for long-term storage
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Aliquoting is necessary for multiple use to avoid repeated freeze-thaw cycles
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Long-term storage should be at -20°C/-80°C
It is important to note that repeated freezing and thawing should be avoided as it can compromise protein integrity and functionality.
How does nuoA contribute to electron transport in the context of quinone diffusion in Roseiflexus castenholzii?
While the search results don't directly address nuoA's specific role in quinone diffusion, we can examine the broader context of quinone-mediated electron transport in R. castenholzii to understand the likely functions of nuoA.
In photosynthetic bacteria like R. castenholzii, the NADH-quinone oxidoreductase complex (which includes nuoA) is responsible for transferring electrons from NADH to quinones in the membrane. These quinones then shuttle electrons to other components of the electron transport chain.
Research on the RC-LH complex in R. castenholzii has revealed that carotenoid assembly regulates quinone diffusion by affecting the architecture of quinone channels . Specifically, carotenoid pigments can block quinone channels between light-harvesting subunits, forming a sealed LH ring that restricts quinone movement .
As a membrane-embedded subunit of the NADH-quinone oxidoreductase complex, nuoA likely participates in:
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Helping form the binding pocket for quinones
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Contributing to the proton pumping mechanism coupled to electron transfer
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Maintaining proper structural conformation of the complex to facilitate quinone binding and release
The research on carotenoid-depleted RC-LH complexes showed accelerated quinone exchange rates due to a larger opening in the LH ring . This suggests that quinone channel architecture and accessibility are critical factors in electron transport efficiency, a process in which nuoA would play an integral role.
What experimental approaches are most effective for studying nuoA interactions with other components of the NADH-quinone oxidoreductase complex?
To effectively study nuoA interactions with other components of the NADH-quinone oxidoreductase complex, researchers should consider a multi-faceted approach:
Structural Biology Techniques:
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Cryo-electron microscopy (cryo-EM): Particularly useful for membrane protein complexes like NADH-quinone oxidoreductase. The high-resolution structures of RC-LH complexes in R. castenholzii have been successfully determined using cryo-EM at 4.1 Å resolution .
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Cross-linking mass spectrometry: This technique can identify interacting partners by chemically linking proteins in close proximity, followed by proteomic analysis.
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Co-immunoprecipitation with tagged nuoA: Using the His-tagged recombinant nuoA to pull down interacting partners.
Functional Interaction Studies:
Based on the research approaches used for studying the RC-LH complex in R. castenholzii, researchers might also consider culturing cells under different light intensities to examine how environmental conditions affect nuoA expression and interactions .
How might nuoA function differ between native and stressed conditions in Roseiflexus castenholzii?
The function of nuoA in R. castenholzii may vary significantly between native and stressed conditions, similar to how carotenoid content and RC-LH complex architecture change in response to environmental factors.
Potential differences under varied light conditions:
Research on R. castenholzii has shown that cells grown under different light intensities (low: 2 μmol m⁻² s⁻¹, medium: 32 μmol m⁻² s⁻¹, and high: 180 μmol m⁻² s⁻¹) display different growth rates and pigmentation . Cells grown under higher light intensities showed faster proliferation rates and darker reddish-brown coloration, indicating altered photosynthetic apparatus composition .
Table 1: Hypothesized Changes in nuoA Function Under Different Conditions
| Condition | Predicted nuoA Expression | Potential Functional Impact | Research Approach |
|---|---|---|---|
| Low Light | Possibly upregulated to maximize energy capture | Enhanced electron transfer efficiency from limited NADH | Quantitative proteomics, RT-qPCR |
| High Light | Potentially downregulated or modified | Adapted electron flow to prevent over-reduction | Activity assays under different light conditions |
| Oxidative Stress | Likely modified to handle increased electron flux | Protection against ROS damage | Redox state analysis of nuoA |
| Nutrient Limitation | Possibly altered to optimize energy conservation | Adjusted proton pumping efficiency | Metabolic flux analysis |
The research on carotenoid-depleted RC-LH complexes revealed that structural changes in photosynthetic complexes can significantly alter quinone exchange rates . By analogy, stress conditions might induce modifications in nuoA that affect its interaction with quinones and other complex components, thereby altering electron transport efficiency in response to environmental challenges.
What are the key experimental design considerations for expressing and purifying functional recombinant nuoA?
Expression System Optimization:
When expressing recombinant Roseiflexus castenholzii nuoA, researchers should consider several factors to ensure production of functional protein:
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Codon optimization: R. castenholzii has different codon usage than E. coli, so codon optimization of the nuoA sequence may improve expression yields.
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Expression temperature: Lower temperatures (16-20°C) often improve membrane protein folding in E. coli, reducing inclusion body formation.
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Induction conditions: Using lower IPTG concentrations (0.1-0.5 mM) and longer induction times can improve proper folding of membrane proteins.
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Host strain selection: E. coli strains designed for membrane protein expression (such as C41(DE3), C43(DE3), or Lemo21(DE3)) may yield better results than standard strains.
Purification Protocol Considerations:
The successful purification of recombinant nuoA requires careful attention to detergent selection and buffer composition:
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Detergent screening: Testing multiple detergents (DDM, LMNG, OG, etc.) to identify optimal solubilization conditions that maintain protein structure and function.
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Buffer optimization: Including stabilizing agents like glycerol (5-20%) and ensuring appropriate pH (typically 7.5-8.0) based on the protein's isoelectric point.
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Purification steps:
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Initial capture using immobilized metal affinity chromatography (IMAC) via the His-tag
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Secondary purification using size exclusion chromatography to separate monomeric protein from aggregates
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Optional ion exchange chromatography for further purification if needed
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Quality control: Assessing protein purity by SDS-PAGE (should exceed 90%) and functional integrity through activity assays.
How can researchers effectively assess the structural integrity and functionality of purified recombinant nuoA?
To comprehensively evaluate both the structural integrity and functionality of purified recombinant nuoA, researchers should employ multiple complementary techniques:
Structural Integrity Assessment:
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Circular Dichroism (CD) Spectroscopy: To evaluate secondary structure content and proper folding, particularly important for alpha-helical membrane proteins like nuoA.
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Thermal Shift Assays: To determine protein stability and the effects of different buffer conditions, detergents, or ligands on protein melting temperature.
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Limited Proteolysis: To probe the accessibility of protease sites, providing information about tertiary structure.
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Size Exclusion Chromatography with Multi-Angle Light Scattering (SEC-MALS): To assess oligomeric state and homogeneity in solution.
Functional Assessment:
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NADH Oxidation Assays: Measuring the rate of NADH oxidation in the presence of quinone analogs to assess electron transfer capability.
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Reconstitution into Liposomes: To evaluate membrane insertion and function in a lipid bilayer environment, which more closely mimics the native context.
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Quinone Binding Assays: Using fluorescent quinone analogs or isothermal titration calorimetry to measure quinone binding affinity and kinetics.
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Proton Pumping Assays: After reconstitution into liposomes, measuring pH changes to assess the protein's ability to participate in proton translocation.
Similar to approaches used in studying RC-LH complexes , researchers might also consider structural analysis by cryo-EM if nuoA can be purified as part of the intact NADH-quinone oxidoreductase complex.
What analytical techniques are most valuable for studying the interaction between nuoA and quinones?
Understanding the interaction between nuoA and quinones is critical for elucidating the protein's role in electron transport. Several analytical techniques are particularly valuable for this purpose:
Spectroscopic Methods:
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UV-Visible Spectroscopy: To monitor quinone reduction states during interaction with nuoA, similar to techniques used for tracking quinone exchange in RC-LH complexes .
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Electron Paramagnetic Resonance (EPR): To detect formation of semiquinone radicals during electron transfer, providing insights into the reaction mechanism.
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Fluorescence Quenching: Using intrinsic tryptophan fluorescence or labeled quinones to measure binding interactions and kinetics.
Binding and Kinetic Analysis:
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Isothermal Titration Calorimetry (ITC): For direct measurement of binding thermodynamics between nuoA and various quinones.
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Surface Plasmon Resonance (SPR): To determine association and dissociation rates of quinone binding to immobilized nuoA.
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Stopped-Flow Spectroscopy: For measuring rapid kinetics of quinone reduction/oxidation when interacting with nuoA.
Structural Approaches:
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Hydrogen-Deuterium Exchange Mass Spectrometry (HDX-MS): To identify regions of nuoA that undergo conformational changes upon quinone binding.
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Molecular Docking and Simulation: To predict quinone binding sites and interaction energies, informing experimental design.
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Photoaffinity Labeling: Using quinone analogs with photoactivatable groups to covalently label residues in the binding site, followed by mass spectrometric identification.
These techniques can be complemented by approaches similar to those used in studying quinone channels in the RC-LH complex of R. castenholzii, where researchers identified how carotenoid assembly affects quinone diffusion .
