Recombinant Cicer arietinum NAD (P)H-quinone oxidoreductase subunit 4L, chloroplastic

What is NAD(P)H-quinone oxidoreductase subunit 4L in chickpea?

NAD(P)H-quinone oxidoreductase subunit 4L (ndhE) is a chloroplastic protein that functions as part of the NAD(P)H dehydrogenase complex in chickpea (Cicer arietinum). This protein belongs to the broader class of oxidoreductases that catalyze electron transfer reactions from an electron donor (reductant) to an electron acceptor (oxidant), typically using nicotinamide adenine dinucleotide phosphate (NADP) or nicotinamide adenine dinucleotide (NAD) as cofactors . In the context of plant biochemistry, this protein plays a crucial role in chloroplastic electron transport chains and contributes to energy metabolism within the plant cell.

The protein is encoded by the ndhE gene and has been assigned the enzyme classification EC 1.6.5.-, indicating its function as an oxidoreductase acting on NADH or NADPH with quinones or similar compounds as electron acceptors .

How do oxidoreductases like NAD(P)H-quinone oxidoreductase function biochemically?

Oxidoreductases catalyze electron transfer reactions by facilitating the movement of electrons from an electron donor (which becomes oxidized) to an electron acceptor (which becomes reduced). In the case of NAD(P)H-quinone oxidoreductase:

• The enzyme binds NADPH or NADH as electron donors

• Electrons are transferred from NAD(P)H to the enzyme's active site

• The enzyme then transfers these electrons to quinones or similar electron acceptors

• This process contributes to redox balance and energy metabolism within the chloroplast

Oxidoreductases play significant roles in both aerobic and anaerobic metabolism and can be found in various biological processes including glycolysis, the TCA cycle, oxidative phosphorylation, and amino acid metabolism . In the specific case of the glycolysis pathway, oxidoreductase enzymes like glyceraldehyde-3-phosphate dehydrogenase accelerate the reduction of NAD .

What biological processes involve NAD(P)H-quinone oxidoreductase in plants?

NAD(P)H-quinone oxidoreductase is involved in several critical biological processes in plants:

• Chloroplast electron transport: Facilitates electron transfer within photosynthetic electron transport chains

• Energy metabolism: Contributes to ATP generation by maintaining electron flow

• Stress response: Participates in plant responses to environmental stressors such as elevated CO₂ concentrations

• Redox homeostasis: Helps maintain the balance of reducing and oxidizing agents within the chloroplast

Under elevated CO₂ conditions, studies have shown that various metabolic pathways in chickpea are affected, including those involving chlorophyll biosynthesis and secondary metabolites production . Since NAD(P)H-quinone oxidoreductase is part of the chloroplastic electron transport system, it likely plays a role in the plant's adaptive response to changing environmental conditions.

What methodologies are recommended for the expression and purification of recombinant NAD(P)H-quinone oxidoreductase?

Expression System Selection:
For the successful expression of recombinant Cicer arietinum NAD(P)H-quinone oxidoreductase subunit 4L, researchers should consider the following methodological approach:

• Vector Selection: Use expression vectors containing strong promoters compatible with either prokaryotic (E. coli) or eukaryotic (yeast, insect, or mammalian) expression systems.

• Expression Host Optimization: For chloroplastic membrane proteins like NAD(P)H-quinone oxidoreductase, specialized expression hosts may be required. Consider:

  • E. coli strains optimized for membrane protein expression (C41, C43)

  • Yeast systems (Pichia pastoris) for proper folding of eukaryotic proteins

  • Cell-free expression systems for toxic or difficult-to-express proteins

• Fusion Tags: Incorporate appropriate fusion tags to aid purification:

  • Hexahistidine (His₆) tag for IMAC purification

  • GST tag for improved solubility

  • MBP tag for enhanced folding

Purification Protocol:
For purification of the recombinant protein, the following multi-step approach is recommended:

• Cell lysis using appropriate buffer systems containing mild detergents (0.5-1% DDM or LDAO) to solubilize membrane-associated proteins

• Initial capture using affinity chromatography based on the fusion tag

• Secondary purification using ion exchange chromatography

• Final polishing step with size exclusion chromatography

• Buffer optimization to maintain protein stability (typically including glycerol at 50% as indicated in the storage recommendations)

The purified protein should be stored in Tris-based buffer with 50% glycerol at -20°C for short-term storage or -80°C for extended storage to maintain stability .

How does NAD(P)H-quinone oxidoreductase expression change under elevated CO₂ conditions?

Research on chickpea response to elevated CO₂ concentrations has revealed significant changes in gene expression patterns related to various metabolic pathways. While specific data on NAD(P)H-quinone oxidoreductase expression is limited in the search results, related findings provide valuable context:

• Transcriptome-wide responses: Studies conducted using open top chambers (OTCs) with chickpea cultivars JG 11 and KAK 2 under ambient (380 ppm) and elevated CO₂ concentrations (550 and 700 ppm) identified 18,644 differentially expressed genes, including 9,687 transcription factors .

• Physiological changes: Elevated CO₂ significantly altered several physiological parameters:

  • Changes in shoot and root length

  • Alterations in nodulation (number of nodules)

  • Modified total chlorophyll content

  • Adjusted nitrogen balance index

• Pathway modulations: A total of 138 pathways were found to be affected, mainly involving:

  • Sugar/starch metabolism

  • Chlorophyll biosynthesis

  • Secondary metabolites biosynthesis

Given that NAD(P)H-quinone oxidoreductase is involved in chloroplastic electron transport, it is likely that its expression and activity are modulated as part of the plant's adaptation to elevated CO₂ levels, potentially through changes in redox state and energy requirements of the chloroplast.

What are the best approaches for analyzing protein-protein interactions involving NAD(P)H-quinone oxidoreductase?

Several methodological approaches can be employed to investigate protein-protein interactions involving NAD(P)H-quinone oxidoreductase:

Yeast Two-Hybrid (Y2H) Analysis:
Y2H systems have been successfully used in chickpea research for studying protein interactions. The methodology involves:

• Constructing bait vectors containing the NAD(P)H-quinone oxidoreductase gene

• Developing prey vectors with potential interacting partners

• Co-transformation into yeast strains

• Selection on appropriate media and reporter gene activation analysis

An example from chickpea research demonstrates this approach: "Transformants with bait and prey were characterized separately to examine two-hybrid interaction between the two proteins in both directions. Colonies were initially patched onto an SC-Leu-Trp master plate before replica-plating onto phenotyping plates: (1) SC-Leu-Trp-Ura to test URA3 activation; (2) SC-Leu-Trp-His + 3-amino-1,2,4-triazole (3-AT) to test HIS3 activation; and (3) YPAD containing a filter for X-gal assay to test lacZ reporter activation."

Co-Immunoprecipitation (Co-IP):
For validating interactions identified through Y2H or for direct investigation of protein complexes:

• Generate antibodies specific to NAD(P)H-quinone oxidoreductase or use tagged versions

• Prepare chloroplast extracts under native conditions

• Perform immunoprecipitation with appropriate antibodies

• Analyze co-precipitated proteins using mass spectrometry

Bimolecular Fluorescence Complementation (BiFC):
For visualizing protein interactions in planta:

• Fuse NAD(P)H-quinone oxidoreductase and potential interactors to complementary fragments of a fluorescent protein

• Express constructs in plant cells (preferably chickpea cells or related species)

• Analyze reconstitution of fluorescence using confocal microscopy

How can researchers measure the enzymatic activity of NAD(P)H-quinone oxidoreductase?

Spectrophotometric Activity Assay:
The enzymatic activity of NAD(P)H-quinone oxidoreductase can be measured using spectrophotometric methods that track the oxidation of NADPH or NADH:

• Reaction Mixture Composition:

  • Buffer: Typically phosphate buffer (pH 7.0-7.4)

  • Substrate: Appropriate quinone (e.g., ubiquinone, decylubiquinone)

  • Cofactor: NADPH or NADH (typically 0.1-0.2 mM)

  • Enzyme: Purified NAD(P)H-quinone oxidoreductase or membrane preparations

• Measurement Parameters:

  • Wavelength: 340 nm (for monitoring NADPH/NADH oxidation)

  • Temperature: 25-30°C

  • Time course: Generally 1-5 minutes to establish initial velocity

• Kinetic Analysis:

  • For substrate affinity determination, vary quinone concentration

  • For cofactor affinity, vary NADPH/NADH concentration

  • Calculate Km values using Lineweaver-Burk or non-linear regression analysis

Based on related research with isoflavone oxidoreductase from chickpea, Km values for NADPH are typically in the micromolar range (approximately 20 μM), though specific values for NAD(P)H-quinone oxidoreductase may differ .

Oxygen Consumption Assay:
For comprehensive analysis of oxidoreductase activity:

• Use oxygen electrode (Clark-type) to measure oxygen consumption

• Reaction mixture should contain the enzyme, appropriate quinone, and NADPH/NADH

• Calculate activity based on the rate of oxygen consumption

What strategies are effective for investigating the role of NAD(P)H-quinone oxidoreductase in chickpea stress responses?

Transcriptional Analysis Approach:
To investigate the role of NAD(P)H-quinone oxidoreductase in stress responses, researchers can employ RNA-Seq analysis similar to studies conducted on chickpea under elevated CO₂:

• Experimental Design:

  • Grow chickpea plants under controlled conditions

  • Apply relevant stress treatments (drought, salinity, temperature extremes)

  • Collect tissue samples at appropriate time points

  • Extract RNA for sequencing

• Data Analysis:

  • Identify differentially expressed genes, focusing on NAD(P)H-quinone oxidoreductase

  • Perform pathway analysis to understand context

  • Validate expression changes using qRT-PCR

A relevant approach is demonstrated in chickpea research where "RNA-Seq from 12 tissues representing vegetative and reproductive growth stages of both cultivars under ambient and elevated CO₂ concentrations identified 18,644 differentially expressed genes including 9,687 transcription factors."

Metabolic Analysis:
To understand the functional impact of NAD(P)H-quinone oxidoreductase in stress responses:

• Measure changes in redox status (NAD+/NADH and NADP+/NADPH ratios)

• Analyze metabolites associated with oxidoreductase activity

• Determine changes in chloroplast electron transport rate

• Assess photosynthetic parameters under stress conditions

Genetic Approaches:
For direct functional investigation:

• RNAi or CRISPR-Cas9 gene editing: Create knockdown or knockout lines

• Overexpression studies: Generate transgenic lines overexpressing NAD(P)H-quinone oxidoreductase

• Phenotypic analysis: Compare stress tolerance between wild-type and modified plants

What are the best storage conditions for recombinant NAD(P)H-quinone oxidoreductase?

For optimal stability and activity retention of recombinant Cicer arietinum NAD(P)H-quinone oxidoreductase, the following storage conditions are recommended:

• Short-term storage (up to one week):

  • Store working aliquots at 4°C in appropriate buffer

• Medium-term storage:

  • Store at -20°C in Tris-based buffer containing 50% glycerol

• Long-term storage:

  • Store at -80°C in small aliquots to minimize freeze-thaw cycles

• Storage buffer composition:

  • Tris-based buffer (typically 20-50 mM, pH 7.5-8.0)

  • 50% glycerol (as cryoprotectant)

  • Additional components optimized for this specific protein

It is important to note that "repeated freezing and thawing is not recommended" as this can lead to protein denaturation and loss of enzymatic activity . For experimental work, prepare small working aliquots to avoid multiple freeze-thaw cycles.

How can researchers verify the identity and purity of recombinant NAD(P)H-quinone oxidoreductase?

To ensure the identity and purity of recombinant NAD(P)H-quinone oxidoreductase, researchers should employ multiple complementary analytical techniques:

Protein Identity Verification:

• Mass Spectrometry Analysis:

  • Tryptic digest followed by LC-MS/MS analysis

  • Verify coverage of at least 80% of the amino acid sequence

• Western Blot Analysis:

  • Use antibodies specific to NAD(P)H-quinone oxidoreductase

  • Alternatively, use antibodies against the fusion tag if present

Purity Assessment:

• SDS-PAGE:

  • Run purified protein on 12-15% gels

  • Stain with Coomassie Blue or silver stain

  • Assess purity by densitometric analysis (aim for >90% purity)

• Size Exclusion Chromatography:

  • Analyze elution profile for homogeneity

  • Determine presence of aggregates or degradation products

• Dynamic Light Scattering:

  • Evaluate size distribution and potential aggregation

  • Assess polydispersity index (aim for <0.2 for high purity)

Functional Verification:

• Enzymatic Activity Assay:

  • Measure NADPH/NADH oxidation rate

  • Compare specific activity with literature values or internal standards

How can NAD(P)H-quinone oxidoreductase research contribute to understanding chickpea stress tolerance?

Research on NAD(P)H-quinone oxidoreductase can significantly contribute to understanding chickpea stress tolerance through several mechanisms:

• Redox Balance Regulation:
  NAD(P)H-quinone oxidoreductase plays a crucial role in maintaining cellular redox homeostasis, which is essential during stress responses. Studies on chickpea mutants have shown that altered redox status can contribute to improved salt stress tolerance, with mutants exhibiting "higher proline that contributes to a better tolerance under salt stress at germination, seedling, and early vegetative phase."

• Photosynthetic Adaptation:
  As a component of chloroplastic electron transport, NAD(P)H-quinone oxidoreductase influences photosynthetic efficiency under stress conditions. Research has shown that chickpea plants under elevated CO₂ display "altered shoot and root length, nodulation (number of nodules), total chlorophyll content and nitrogen balance index, significantly." Understanding the role of NAD(P)H-quinone oxidoreductase in these adaptations could provide insights into stress tolerance mechanisms.

• Metabolic Network Integration:
  NAD(P)H-quinone oxidoreductase functions within broader metabolic networks that respond to environmental stresses. Transcriptome profiling of chickpea under elevated CO₂ has identified "138 pathways, mainly involved in sugar/starch metabolism, chlorophyll and secondary metabolites biosynthesis," revealing the "crosstalk operating behind the responses of chickpea to elevated CO₂ concentration." Studying NAD(P)H-quinone oxidoreductase within this context can help elucidate its contribution to metabolic adaptations under stress.

What are the potential biotechnological applications of research on chickpea NAD(P)H-quinone oxidoreductase?

Research on chickpea NAD(P)H-quinone oxidoreductase has several potential biotechnological applications:

• Crop Improvement Strategies:
  Understanding the role of NAD(P)H-quinone oxidoreductase in stress responses could inform breeding programs aimed at developing chickpea varieties with enhanced tolerance to environmental stresses. This is particularly relevant as studies have identified "molecular and physiological alterations in chickpea under elevated CO₂ concentrations," highlighting the importance of understanding metabolic adaptations in changing climates.

• Biocatalysis Applications:
  Oxidoreductases have significant potential in biotechnology for catalyzing specific redox reactions. As noted, "it has long been an important goal in biotechnology to develop practical biocatalytic applications of oxidoreductases. During the past few years, significant breakthrough has been made in the development of oxidoreductase-based diagnostic tests and improved biosensors, and the design of innovative systems for the regeneration of essential coenzymes."

• Biosensor Development:
  NAD(P)H-quinone oxidoreductase could be utilized in the development of biosensors for monitoring redox status or detecting specific quinone compounds in agricultural or environmental samples.

• Metabolic Engineering:
  Knowledge of NAD(P)H-quinone oxidoreductase function could inform metabolic engineering approaches aimed at improving plant performance under stress conditions or enhancing the production of valuable secondary metabolites.

How does chickpea NAD(P)H-quinone oxidoreductase compare to similar enzymes in other plant species?

A comparative analysis of chickpea NAD(P)H-quinone oxidoreductase with similar enzymes from other plant species reveals important evolutionary and functional insights:

Structural Comparisons:
While specific comparative data for NAD(P)H-quinone oxidoreductase is limited in the search results, related research on other oxidoreductases from chickpea provides valuable context. For instance, NADPH:isoflavone oxidoreductase (IFR) from chickpea has been characterized as "a single polypeptide with a molecular mass of 36 kDa" with specific substrate requirements including "a 2′-hydroxy group and a 4′,5′-methylenedioxy or 4′-methoxy function" for substrate acceptance.

Functional Conservation:
The NAD(P)H-quinone oxidoreductase gene appears to be conserved across plant species, particularly within legumes. Research suggests that in chickpea, certain genes are "present as a single copy in chickpea and related legumes of the galegoid clade" , which may also apply to the NAD(P)H-quinone oxidoreductase gene.

Evolutionary Relationships:
Phylogenetic analysis of oxidoreductases across plant species can provide insights into their evolutionary history and functional diversification. Though specific data on NAD(P)H-quinone oxidoreductase phylogeny is not present in the search results, such analysis would be valuable for understanding the conservation and specialization of this enzyme across different plant taxa.

What methodological challenges are specific to working with chickpea NAD(P)H-quinone oxidoreductase?

Researchers working with chickpea NAD(P)H-quinone oxidoreductase face several methodological challenges that require specific technical approaches:

Membrane Protein Isolation:
As a chloroplastic protein likely embedded in thylakoid membranes, NAD(P)H-quinone oxidoreductase presents challenges for isolation and purification. Effective solubilization requires careful selection of detergents and buffer conditions to maintain native structure and function.

Activity Preservation:
Maintaining enzymatic activity during purification and storage is crucial. The recommended storage in "Tris-based buffer, 50% glycerol, optimized for this protein" at appropriate temperatures (-20°C or -80°C for extended storage) highlights the importance of optimized conditions to preserve activity.

Expression Systems:
Heterologous expression of chloroplastic membrane proteins often presents challenges regarding proper folding, localization, and post-translational modifications. Selecting appropriate expression systems and optimization of expression conditions is critical for obtaining functional recombinant protein.

Assay Development: Developing reliable and sensitive assays for NAD(P)H-quinone oxidoreductase activity requires careful consideration of substrate specificity, cofactor requirements, and potential interference from other cellular components.