Recombinant Trachelium caeruleum NAD (P)H-quinone oxidoreductase subunit 4L, chloroplastic

What is the Trachelium caeruleum NAD(P)H-quinone oxidoreductase subunit 4L protein and where is it located?

The NAD(P)H-quinone oxidoreductase subunit 4L (ndhE gene product) is a chloroplastic protein from Trachelium caeruleum (Blue throatwort) that functions as part of the NAD(P)H dehydrogenase complex. This protein is localized in the chloroplast and is involved in electron transport chains. It is also alternatively known as NAD(P)H dehydrogenase subunit 4L or NADH-plastoquinone oxidoreductase subunit 4L with an EC classification of 1.6.5.- . This protein is part of a complex that catalyzes the transfer of electrons from NAD(P)H to quinones, a critical component of photosynthetic and respiratory electron transport.

What is the complete amino acid sequence and structure of the protein?

The complete amino acid sequence of Trachelium caeruleum NAD(P)H-quinone oxidoreductase subunit 4L consists of 100 amino acids:

mLEHVLVLSAYLFSVGLYGLITSRNMVRALICLELIFNAVNINFVTFSDFFDSRHLKGSIFAIFVIAIAAAEAAIGLAILSAIYRNRKSIHINQSNLLTK

The protein has a UniProt accession number of A9QC58. The expression region spans positions 1-100, confirming it as a full-length protein . As a membrane-bound component of the NAD(P)H dehydrogenase complex, this protein likely contains transmembrane domains, which is suggested by the hydrophobic amino acid stretches in its sequence.

How does the genomic context affect our understanding of this protein?

The ndhE gene encoding this protein exists within one of the most highly rearranged chloroplast genomes among land plants. The Trachelium caeruleum chloroplast genome is 162,321 bp with an inverted repeat (IR) of 27,273 bp, a large single-copy (LSC) region of 100,114 bp, and a small single-copy (SSC) region of 7,661 bp . This unusual genomic organization provides important context for understanding the protein's evolution and expression.

The genome encodes 112 different genes, with some duplicated in the IR regions. Unlike many other chloroplast proteins in Trachelium, the ndhE gene appears to be intact, whereas related genes like ndhK may be pseudogenes containing internal stop codons . This suggests selective evolutionary pressure to maintain the function of ndhE despite extensive genome rearrangements.

What are the structural and functional implications of genomic rearrangements on the NAD(P)H-quinone oxidoreductase complex?

The chloroplast genome of Trachelium caeruleum contains 18 conserved blocks of genes that have been extensively rearranged relative to the ancestral angiosperm gene order found in Nicotiana . These rearrangements include numerous large inversions, gene duplications, and gene reductions.

The ndh gene family, which includes ndhE, is part of this rearranged genome landscape. Notably, while ndhE appears intact, the related ndhK gene contains multiple internal stop codons generated by a single deletion causing a frameshift and several additional indels . This creates an interesting research question regarding how the NAD(P)H dehydrogenase complex remains functional despite alterations to some of its components.

Studies of NAD(P)H/quinone oxidoreductases in other organisms suggest a ping-pong catalytic mechanism, where conformational changes control access to the catalytic site as substrates bind and products are released . Researchers should consider how the specific sequence of the Trachelium caeruleum enzyme might influence this mechanism, particularly considering the extensive genomic rearrangements observed.

How do repeats and tRNA genes influence the evolution of the ndhE gene?

The Trachelium caeruleum chloroplast genome contains numerous repeat elements associated with genomic rearrangements. These repeats are generally clustered at or near rearrangement endpoints and have diverse origins, including partial or entire chloroplast gene duplications, noncoding chloroplast sequences, or novel DNA .

tRNA genes are found at the ends of 10 of 18 rearranged blocks of genes in Trachelium, suggesting their potential role in facilitating inversions . Researchers investigating the evolution of ndhE should examine whether it is located near such repeat elements or tRNA genes, as this may provide insight into its evolutionary history and functional conservation despite the dramatic genomic rearrangements in this species.

The high incidence of dispersed repetitive DNA is clearly associated with the unusual organization of the Trachelium chloroplast genome . Understanding how these repeats influence gene expression and protein function represents an important research direction.

What experimental approaches are optimal for studying the function of this recombinant protein?

To study the function of recombinant Trachelium caeruleum NAD(P)H-quinone oxidoreductase subunit 4L, researchers should consider multiple experimental approaches:

• Heterologous expression systems: E. coli or yeast expression systems can be used to produce sufficient quantities of the recombinant protein for biochemical and structural studies.

• Activity assays: Enzyme activity can be measured spectrophotometrically by monitoring NAD(P)H oxidation at 340 nm in the presence of various quinone substrates.

• Site-directed mutagenesis: Key amino acid residues predicted to be involved in catalysis or substrate binding can be mutated to determine their functional importance.

• Protein-protein interaction studies: Techniques such as co-immunoprecipitation, yeast two-hybrid assays, or pull-down assays can identify interaction partners within the NAD(P)H dehydrogenase complex.

• Structural studies: X-ray crystallography or cryo-electron microscopy can elucidate the three-dimensional structure, similar to the approaches used for human and mouse NAD(P)H:quinone oxidoreductases .

What protein purification and storage protocols are recommended for this recombinant protein?

Based on available information about the recombinant Trachelium caeruleum NAD(P)H-quinone oxidoreductase subunit 4L, the following purification and storage protocols are recommended:

Storage conditions:

• Store at -20°C for general storage

• For extended storage, conserve at -20°C or -80°C

• Prepare working aliquots and store at 4°C for up to one week

• Avoid repeated freezing and thawing cycles as this may compromise protein integrity

Buffer composition:

• Use Tris-based buffer with 50% glycerol, optimized specifically for this protein

• The buffer conditions should be maintained at physiological pH (typically 7.2-7.5)

Additional purification recommendations based on similar proteins would include affinity chromatography (if expressed with a tag) followed by size exclusion chromatography to ensure high purity.

What are the optimal assay conditions for measuring enzymatic activity?

While specific assay conditions for Trachelium caeruleum NAD(P)H-quinone oxidoreductase subunit 4L are not directly provided in the search results, researchers can adapt methods used for similar enzymes:

• Substrate selection: Various quinones can serve as electron acceptors, including duroquinone (2,3,5,6-tetramethyl-p-benzoquinone), which has been used as a substrate for human NAD(P)H-quinone oxidoreductase .

• Reaction monitoring: The reaction can be monitored by following the decrease in NADPH or NADH absorbance at 340 nm.

• Temperature and pH: Most plant chloroplastic enzymes function optimally at 25-30°C and pH 7.0-8.0.

• Control experiments: Include proper controls such as heat-inactivated enzyme and reactions without substrate or cofactor.

A typical enzyme activity assay would contain:

• Buffer (e.g., 50 mM Tris-HCl, pH 7.5)

• NAD(P)H (100-200 μM)

• Quinone substrate (50-100 μM)

• Recombinant enzyme (0.1-1 μg)

• Optional additives: BSA or other stabilizers

How can researchers confirm the correct folding and functionality of the recombinant protein?

Several approaches can be used to verify proper folding and functionality:

• Circular dichroism (CD) spectroscopy: To assess secondary structure elements and proper folding.

• Size exclusion chromatography: To confirm the expected oligomeric state (likely dimeric or tetrameric based on related enzymes).

• Thermal shift assays: To evaluate protein stability under various conditions.

• Enzyme activity assays: As described above, to confirm catalytic functionality.

• Binding studies: Using isothermal titration calorimetry (ITC) or surface plasmon resonance (SPR) to measure binding affinities for substrates and cofactors.

• Limited proteolysis: To probe the accessibility of cleavage sites as an indicator of proper folding.

How does this protein compare to NAD(P)H-quinone oxidoreductases in other species?

The NAD(P)H-quinone oxidoreductase family has been characterized across various species. While the search results don't provide direct comparisons for the Trachelium caeruleum enzyme, we can infer some comparative aspects:

• Sequence conservation: The protein likely shares functional domains with other plant NAD(P)H-quinone oxidoreductases but may have unique features related to its specific role in Trachelium caeruleum.

• Mechanism comparison: The plant chloroplastic enzyme is part of the NDH complex involved in cyclic electron flow around photosystem I, whereas the mammalian enzyme (NQO1/QR1) serves primarily in detoxification of quinones and protection from oxidative stress .

• Structural differences: The human and mouse NQO1 enzymes have been structurally characterized, revealing important features of substrate binding and catalysis . The plant enzymes likely have evolved distinct structural adaptations for their chloroplastic functions.

• Evolutionary significance: The persistence of ndhE in the highly rearranged Trachelium chloroplast genome suggests important functional constraints despite dramatic genomic reorganization .

What can the Trachelium caeruleum chloroplast genome tell us about the evolution of ndh genes?

The Trachelium caeruleum chloroplast genome provides a remarkable case study in genomic plasticity and evolution:

• Selective pressures: While some genes (ycf15, rpl23, infA, and accD) are truncated or reduced to gene fragments in Trachelium, ndhE appears to be intact, suggesting differential selective pressures on various chloroplast genes .

• Gene rearrangements: The extensive rearrangements in the Trachelium chloroplast genome have resulted in 18 conserved blocks of genes being extensively reordered and inverted compared to the ancestral angiosperm gene order . How these rearrangements affect the coordinated expression of ndh genes remains an important research question.

• Correlation with repeats: The high number and large size of repeats in the Trachelium chloroplast genome correlate with its extensive rearrangements . These repeats may have played a role in the evolutionary history of ndh genes.

• Comparative context: Among angiosperms, Trachelium has one of the most highly rearranged chloroplast genomes, along with Pelargonium and to a lesser extent Jasminum . Comparing ndh gene organization across these species could provide insights into the evolutionary forces shaping these genes.

What are the best expression systems for producing this recombinant protein for research?

When choosing an expression system for Trachelium caeruleum NAD(P)H-quinone oxidoreductase subunit 4L, researchers should consider:

For chloroplast membrane proteins like this one, inclusion of appropriate detergents during purification will be critical for maintaining protein stability and function.

What are the key research questions that remain unanswered about this protein?

Several important questions remain to be addressed regarding Trachelium caeruleum NAD(P)H-quinone oxidoreductase subunit 4L:

• Functional significance: How does this protein contribute to electron transport in Trachelium caeruleum chloroplasts, and is its function identical to homologs in plants with less rearranged genomes?

• Structural determinants of function: What are the key residues involved in substrate binding and catalysis?

• Protein interactions: What are its binding partners within the NDH complex, and how do these interactions influence function?

• Evolutionary adaptation: Has the protein evolved unique properties related to the extensive genomic rearrangements in Trachelium caeruleum?

• Regulatory mechanisms: How is the expression of ndhE regulated in the context of the highly rearranged chloroplast genome?

Addressing these questions will require a combination of biochemical, structural, and genetic approaches, building upon our current understanding of NAD(P)H-quinone oxidoreductases and the unique genomic context of Trachelium caeruleum.