Recombinant Roseiflexus sp. NADH-quinone oxidoreductase subunit K (nuoK)

Where was Roseiflexus sp. RS-1 originally isolated and what are its growth characteristics?

Roseiflexus sp. RS-1 was isolated from the phototrophic microbial mats of Octopus Spring in Yellowstone National Park at 60°C . It is a gliding, filamentous bacterium belonging to the phylum Chloroflexi, which is a deep-branching lineage of Bacteria . This organism demonstrates remarkable metabolic versatility, with the ability to:

• Grow optimally as a photoheterotroph

• Function as an aerobic heterotroph

• Potentially perform photoautotrophy using the 3-hydroxypropionate pathway

• Utilize small concentrations of sulfide (120-240 μM) as an electron donor

• Grow on acetate, pyruvate, and other organic acids when supplemented with 0.2% yeast extract

Molecular analyses have shown that Roseiflexus spp. are the dominant filamentous anoxygenic phototrophs (FAPs) in the mats of Octopus Spring at this temperature .

How is recombinant Roseiflexus sp. nuoK typically prepared for research applications?

The recombinant protein is typically prepared through heterologous expression systems. Based on the product information available, the preparation involves the following methodology:

• Expression and Purification Process:

  • The full-length protein (amino acids 1-100) is expressed in a suitable host system

  • The tag type is determined during the production process based on optimal expression and purification requirements

  • Purification likely involves affinity chromatography followed by additional purification steps

• Storage and Handling:

  • The purified protein is supplied in a Tris-based buffer containing 50% glycerol, specifically optimized for this protein

  • For extended storage, the protein should be conserved at -20°C or -80°C

  • Repeated freezing and thawing is not recommended

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

• Available Formulation:

  • Standard quantity: 50 μg (other quantities may be available upon request)

  • The protein is supplied at a concentration appropriate for experimental applications

For experimental reproducibility, researchers should note the specific batch information and storage conditions when using this recombinant protein in their studies.

How does nuoK contribute to the photometabolic capabilities of Roseiflexus sp.?

The nuoK subunit, as part of the NADH-quinone oxidoreductase complex, plays an important role in the unique photometabolic capabilities of Roseiflexus sp.:

• Integration with Photosynthetic Apparatus:

  • Roseiflexus sp. contains Type II reaction centers and bacteriochlorophyll a-containing light-harvesting complexes

  • Unlike related Chloroflexus aurantiacus, Roseiflexus spp. do not synthesize bacteriochlorophyll c and lack chlorosomes

  • The NADH-quinone oxidoreductase complex links respiratory electron transport with photosynthetic energy conservation

• Support for Metabolic Flexibility:

  • The complex facilitates electron flow during:

    • Photoheterotrophic growth (optimal growth mode in culture)

    • Aerobic heterotrophic metabolism

    • Potential photoautotrophic growth via the 3-hydroxypropionate pathway

• In situ Functionality:

  • Light-stimulated uptake studies using 13C-labeled bicarbonate, acetate, and propionate demonstrate that Roseiflexus spp. perform both photoautotrophy and photoheterotrophy in their natural environment

  • The NADH-quinone oxidoreductase complex, including nuoK, supports these metabolic processes by facilitating appropriate electron flow depending on available energy and carbon sources

The nuoK subunit thus forms part of the bioenergetic machinery that enables Roseiflexus sp. to thrive in the specialized ecological niche of hot spring microbial mats.

What are the structural characteristics of the nuoK protein in Roseiflexus sp.?

Based on its amino acid sequence and the known functions of NADH-quinone oxidoreductase subunit K proteins, the Roseiflexus sp. nuoK exhibits several key structural characteristics:

• Membrane Protein Features:

  • The sequence (MVPTSYYILLSALLFTLGVAGVLIRRNALVLFMSVELMLNSANLALVTFAMARQDIAGQIVVFFVIVVAAAEVAVGLALLVAIFRTKQTTDVDEIHSLKG) indicates a highly hydrophobic protein consistent with membrane integration

  • Multiple predicted transmembrane helices span the membrane

• Conserved Domains:

  • As part of the NuoK family (NADH:ubiquinone oxidoreductase subunit K), it contains structural motifs conserved across this protein family

  • Key functional regions likely include those involved in:

    • Interaction with other Complex I subunits

    • Proton channel formation

    • Maintenance of proper membrane topology

• Thermostable Adaptations:

  • Given that Roseiflexus sp. RS-1 was isolated from a hot spring environment (60°C), the nuoK protein likely contains structural features that enhance thermostability

  • These may include increased hydrophobic interactions, optimized salt bridges, and reduced flexibility in certain regions

• Post-Translational Considerations:

  • The protein may undergo post-translational modifications that affect its integration into the larger NADH-quinone oxidoreductase complex

  • The native membrane environment plays a critical role in maintaining the proper structural conformation

Understanding these structural characteristics is essential for researchers designing experiments involving this protein, particularly when considering functional studies or structural analyses.

What experimental approaches are most effective for studying nuoK function in Roseiflexus sp.?

For rigorous investigation of nuoK function in Roseiflexus sp., several advanced experimental approaches can be employed:

• Site-Directed Mutagenesis and Functional Analysis:

  • Identify conserved residues in the nuoK sequence through comparative analysis

  • Generate point mutations using site-directed mutagenesis

  • Express and purify the mutant proteins

  • Assess the impact on:

    • NADH:quinone oxidoreductase activity using spectrophotometric assays

    • Proton pumping efficiency using pH-sensitive fluorescent probes

    • Complex assembly using Blue Native PAGE

• Protein-Protein Interaction Studies:

  • Apply crosslinking approaches coupled with mass spectrometry

  • Use co-immunoprecipitation with tagged versions of nuoK

  • Perform FRET (Förster Resonance Energy Transfer) analysis to study dynamic interactions within the complex

• Biophysical Characterization:

  • Employ EPR (Electron Paramagnetic Resonance) spectroscopy to examine the local environment of specific amino acids

  • Use CD (Circular Dichroism) spectroscopy to analyze secondary structure elements and thermal stability

  • Apply hydrogen-deuterium exchange mass spectrometry to identify solvent-accessible regions

• Structural Biology Approaches:

  • Attempt crystallization of the recombinant protein or the entire complex

  • Use single-particle cryo-electron microscopy to elucidate the structure of the complex

  • Apply NMR for structural studies of specific domains or peptide fragments

• Proteoliposome Reconstitution:

  • Reconstitute purified nuoK with other components of the NADH-quinone oxidoreductase complex in artificial membrane systems

  • Monitor electron transfer and proton pumping activities

  • Test the effects of lipid composition on protein function

These methodologies should be selected based on the specific research question, available resources, and the particular challenges associated with working with membrane proteins from thermophilic organisms.

How can recombinant nuoK be incorporated into reconstituted electron transport chain models?

Incorporating recombinant Roseiflexus sp. nuoK into reconstituted electron transport chain (ETC) models requires careful experimental design:

• Proteoliposome System Development:

  • Prepare liposomes with defined lipid composition mimicking the native membrane environment

  • Incorporate purified recombinant nuoK along with other required complex I components

  • Verify successful incorporation using appropriate assays

  Component	Specification	Purpose
  Lipid composition	70% POPC, 20% POPE, 10% cardiolipin	Mimic bacterial membrane environment
  Proton indicator	ACMA or pyranine	Monitor proton translocation
  Electron donor	NADH (100-500 μM)	Provide electrons to the system
  Electron acceptor	Ubiquinone analogs	Accept electrons from Complex I
  Temperature range	25-70°C	Assess temperature-dependent activity

• Minimal ETC Reconstruction:

  • Create simplified electron transport chains containing:

    • NADH dehydrogenase complex (including nuoK)

    • Appropriate quinones

    • Terminal electron acceptors

  • Measure electron transfer rates and proton translocation efficiencies

  • Assess the impact of different quinone species on activity

• Chimeric Complex Construction:

  • Replace the nuoK subunit in Complex I from model organisms with the Roseiflexus sp. variant

  • Analyze how the thermophilic nuoK affects complex stability and function

  • Identify structural determinants of thermal stability and functional properties

• Nanodisk Technology Application:

  • Incorporate recombinant nuoK into nanodisks for single-molecule studies

  • Use this system to examine the dynamics of proton pumping

  • Apply advanced microscopy techniques to visualize conformational changes

By systematically implementing these approaches, researchers can gain insights into how the Roseiflexus sp. nuoK contributes to electron transport and energy conservation in thermophilic environments, potentially leading to applications in bioenergetics research and biotechnology.

What structural modeling techniques provide insights into nuoK's role in the NADH-quinone oxidoreductase complex?

Advanced computational and structural modeling approaches can significantly enhance our understanding of nuoK's functional role:

• Homology Modeling Workflow:

  • Identify structural templates through database searches

  • Generate models using platforms such as SWISS-MODEL, Phyre2, or I-TASSER

  • Refine models using energy minimization and molecular dynamics

  • Validate structural quality using metrics such as QMEAN, DOPE score, and Ramachandran plots

• Molecular Dynamics Simulations:

  • Embed the modeled nuoK structure in a lipid bilayer simulation

  • Perform extended simulations (>100 ns) under conditions mimicking the thermophilic environment

  • Analyze:

    • Protein stability in the membrane

    • Water molecule pathways that might indicate proton translocation routes

    • Conformational changes in response to different states of the catalytic cycle

• Integrative Structural Biology Approach:

  Stage	Method	Expected Outcome
  1	Sequence analysis	Identification of transmembrane regions and conserved motifs
  2	Initial model building	Template-based structural model
  3	Membrane embedding	Protein properly oriented in simulated lipid environment
  4	Simulation equilibration	Stable system preparation
  5	Production runs	Trajectory for detailed analysis
  6	Analysis of dynamics	Identification of key functional motifs and movements
  7	Integration with experimental data	Refined and validated structural model
  8	Functional annotation	Proposed structure-function relationships

• Quantum Mechanics/Molecular Mechanics (QM/MM):

  • Apply QM/MM to study potential proton transfer events

  • Focus computational resources on catalytically important regions

  • Calculate energy barriers for proton transfer steps

• Protein-Protein Docking:

  • Model the interfaces between nuoK and adjacent subunits

  • Predict key residues involved in subunit interactions

  • Simulate the assembly of the membrane domain

These computational methods, especially when integrated with experimental data, provide valuable insights into how nuoK contributes to the structure and function of the NADH-quinone oxidoreductase complex in Roseiflexus sp., particularly in relation to its thermophilic adaptations.

How does environmental temperature affect nuoK function in Roseiflexus sp., and what methodologies can assess this relationship?

As a thermophilic organism isolated from hot springs at 60°C, Roseiflexus sp.'s nuoK protein has likely evolved specific adaptations to function optimally at elevated temperatures. Investigating this temperature-function relationship requires sophisticated methodological approaches:

• Temperature-Dependent Activity Profiling:

  • Purify recombinant nuoK or prepare membrane vesicles containing the NADH-quinone oxidoreductase complex

  • Measure enzymatic activity across a temperature range (e.g., 30-80°C)

  • Determine temperature optima and generate Arrhenius plots to calculate activation energies

  • Compare with homologous proteins from mesophilic organisms

• Thermal Stability Assessment:

  • Apply differential scanning calorimetry (DSC) to determine melting temperatures

  • Use circular dichroism (CD) spectroscopy to monitor secondary structure changes with temperature

  • Perform thermal shift assays to identify stabilizing conditions

  • Monitor time-dependent activity loss at different temperatures

• Controlled Environmental Studies:

  • Culture Roseiflexus sp. at different temperatures within its growth range

  • Isolate membrane fractions and measure NADH-quinone oxidoreductase activity

  • Quantify nuoK expression levels using qRT-PCR and proteomics

  • Analyze membrane lipid composition changes that might affect nuoK function

• In Situ Ecological Measurements:

  • Sample natural hot spring environments with temperature gradients

  • Measure Roseiflexus sp. abundance and metabolic activity

  • Correlate with nuoK expression and NADH-quinone oxidoreductase activity

  • Create temperature microenvironment models to understand ecological significance

• Experimental Matrix Design:

  Temperature (°C)	Parameter	Measurement Endpoints
  45	Below optimal	Enzyme activity, stability, expression levels
  55	Near optimal	Kinetic parameters, membrane incorporation
  60	Optimal (isolation temperature)	Baseline measurements for all parameters
  65	Above optimal	Stress responses, protein modifications
  70	Upper limit	Denaturation rates, activity loss kinetics

By employing these methodologies, researchers can elucidate how temperature affects nuoK function, providing insights into the molecular adaptations that enable Roseiflexus sp. to thrive in thermophilic environments and potentially informing biotechnological applications requiring thermostable electron transport components.

What analytical techniques can be used to study post-translational modifications of nuoK and their functional significance?

Post-translational modifications (PTMs) can significantly impact the function, stability, and interactions of membrane proteins like nuoK. Advanced analytical techniques to investigate these modifications include:

• Mass Spectrometry-Based PTM Identification:

  • Employ bottom-up proteomics approaches:

    • Digest purified nuoK with proteases (trypsin, chymotrypsin, or combinations)

    • Analyze resulting peptides using LC-MS/MS

    • Apply electron transfer dissociation (ETD) or electron capture dissociation (ECD) for labile modifications

  • Use top-down proteomics to analyze the intact protein:

    • Directly introduce purified nuoK into a high-resolution mass spectrometer

    • Analyze fragmentation patterns to localize modifications

    • Quantify the stoichiometry of different modified forms

• Site-Specific Analysis Methods:

  • Develop antibodies against specific modified forms of nuoK

  • Apply site-directed mutagenesis to potential modification sites

  • Use chemical probes that react with specific modifications

  • Perform targeted MS approaches (multiple reaction monitoring) for quantitative analysis

• Functional Impact Assessment:

  • Compare the activity of differentially modified forms of nuoK

  • Analyze how modifications affect:

    • Protein-protein interactions within the complex

    • Proton pumping efficiency

    • Temperature stability

    • Membrane integration

• Environmental Regulation Studies:

  • Investigate how growth conditions affect the PTM profile:

    • Temperature variations

    • Light intensity and wavelength

    • Carbon source availability

    • Redox state of the cellular environment

• Modification-Specific Structural Analysis:

  Modification Type	Analytical Method	Functional Assessment
  Phosphorylation	Phosphoproteomic MS, Phos-tag gels	Kinase inhibitors, phosphomimetic mutations
  Oxidative modifications	Redox proteomics, DNPH derivatization	Antioxidant treatments, oxidation-resistant mutants
  Lipid modifications	Lipidomics, click chemistry	Lipid synthesis inhibitors, site-directed mutagenesis
  Glycosylation	Glycoproteomic MS, lectin affinity	Glycosidase treatments, glycosylation site mutations

• Temporal Dynamics Investigation:

  • Pulse-chase experiments to determine modification kinetics

  • Time-course studies during adaptive responses

  • Analysis of modification patterns during complex assembly

These analytical approaches provide a comprehensive framework for understanding how post-translational modifications regulate nuoK function in Roseiflexus sp., potentially revealing novel mechanisms of regulation in thermophilic electron transport systems and identifying targets for engineering enhanced electron transport chains for biotechnological applications.