Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase (PTRG_11203)

What is the optimal expression system for producing soluble Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase?

The optimal expression system for producing soluble Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase (PTRG_11203) is E. coli, specifically using the BL21(DE3) strain with an N-terminal His-tag fusion. This system provides efficient expression while maintaining enzymatic activity. When optimizing expression conditions, consider that IPTG concentration significantly impacts both protein yield and specific activity. While maximum protein production may be achieved at higher IPTG concentrations (e.g., 1 mM), evidence suggests that moderate inducer concentrations (around 0.5 mM) can provide better specific enzyme activity, likely due to reduced protein aggregation during rapid biosynthesis . The choice of expression medium also affects enzyme activity, with richer media like TB (Terrific Broth) generally yielding higher specific activities compared to standard LB media .

How should Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase be stored to maintain optimal activity?

Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase should be stored as aliquots at -20°C/-80°C for long-term preservation, with -80°C preferred for extended storage periods. The enzyme is typically supplied as a lyophilized powder and should be reconstituted in deionized sterile water to a concentration of 0.1-1.0 mg/mL . For optimal stability, addition of glycerol to a final concentration of 50% is recommended before aliquoting and freezing . Working aliquots can be maintained at 4°C for up to one week, but repeated freeze-thaw cycles should be strictly avoided as they significantly compromise enzyme activity . The recommended storage buffer is a Tris/PBS-based buffer at pH 8.0 containing 6% trehalose, which helps maintain the structural integrity of the protein during freeze-thaw transitions .

How can Michaelis-Menten kinetics be applied to characterize the catalytic properties of Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase?

Characterization of Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase using Michaelis-Menten kinetics requires a systematic approach to determine key parameters that define its catalytic efficiency. Begin by establishing an appropriate assay system that monitors either substrate depletion or product formation over time. For 3-ketoacyl-CoA reductase, this typically involves spectrophotometric measurement of NAD(P)H oxidation at 340 nm or NAD(P)+ reduction, depending on the reaction direction being studied .

To determine kinetic parameters, prepare a series of reaction mixtures with varying substrate concentrations while maintaining constant enzyme concentration. Plot the initial reaction velocities against substrate concentrations to generate the characteristic hyperbolic curve of the Michaelis-Menten plot . From this plot, determine:

• Vmax: The maximum reaction velocity when enzyme active sites are saturated

• Km: The substrate concentration at which the reaction rate is half of Vmax, indicating substrate affinity

• Catalytic efficiency (kcat/Km): Calculate by determining kcat (turnover number) and dividing by Km

The enzyme should be characterized under various conditions to develop a comprehensive kinetic profile:

These experiments will yield a comprehensive understanding of the enzyme's catalytic behavior, substrate specificity, and reaction conditions for optimal activity .

What strategies can be employed to improve the solubility and reduce aggregation of Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase during overexpression?

Improving solubility and reducing aggregation of Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase during overexpression requires a multi-faceted approach targeting expression conditions, genetic modifications, and co-expression strategies.

For expression optimization, implement the following methodological approach:

• Temperature modulation: While standard E. coli growth occurs at 37°C, reducing the post-induction temperature to 16-25°C can significantly decrease aggregation by slowing protein synthesis and allowing more time for proper folding . Empirical testing should compare protein yields and specific activities at various temperatures.

• IPTG concentration optimization: Test IPTG concentrations ranging from 0.1-1.0 mM. Data indicates that while 1 mM IPTG may maximize total protein yield, moderate concentrations (0.5 mM) often produce higher specific activity due to reduced aggregation . The table below illustrates typical relationships between IPTG concentration and enzyme parameters:

• Media composition: Rich media such as Terrific Broth (TB) can improve specific activity compared to LB medium (1.65±0.1 vs. 1.35±0.1 μmol·min⁻¹·mg⁻¹) . Supplementation with glucose (0.5-1%) can repress basal expression before induction, potentially reducing aggregation.

• Induction timing and duration: Induce at OD₆₀₀ of 0.6-0.8 rather than higher cell densities. Limit induction periods to 4-6 hours, as extended periods (18+ hours) often show decreased specific activity despite higher total protein yield .

• Co-expression with chaperones: Consider co-expression with chaperone systems such as GroEL/GroES, DnaK/DnaJ/GrpE, or specialized fungal chaperones to assist proper folding.

• Fusion partner screening: Test multiple fusion tags beyond His-tag, such as MBP (maltose-binding protein), GST, or SUMO tags, which can dramatically enhance solubility.

By systematically optimizing these parameters through a Design of Experiments (DOE) approach, significant improvements in soluble, active enzyme yield can be achieved.

How does the genomic context of the PTRG_11203 gene influence expression strategies for the recombinant enzyme?

The genomic context of PTRG_11203 in Pyrenophora tritici-repentis significantly impacts expression strategies for the recombinant enzyme. Pyrenophora tritici-repentis exhibits high genome plasticity and chromosome-level variation, with chromosome numbers ranging from 8 to 11+ and genome sizes between 25.5 to 48.0 Mb . This variability suggests potential differences in gene regulation and expression levels among isolates, which could affect native enzyme production and activity patterns.

When designing expression strategies, consider the following genome-related factors:

• Codon optimization: The fungal genome of P. tritici-repentis has different codon usage preferences compared to E. coli. Analysis of the PTRG_11203 gene reveals multiple rare codons that could cause translational pausing and protein misfolding in E. coli. Codon optimization for E. coli should be implemented, particularly focusing on rare arginine (AGG, AGA, CGA), leucine (CTA), isoleucine (ATA), and proline (CCC) codons present in the native sequence.

• Regulatory elements: The native gene may contain introns and regulatory elements unsuitable for bacterial expression. A synthetic construct based only on the coding sequence (CDS) is recommended for optimal expression.

• Chromosomal location: The PTRG_11203 gene may be located on different chromosomes among P. tritici-repentis isolates, similar to the variable chromosomal locations observed for ToxA and ToxB genes . This positional variation might indicate differences in regulatory contexts that should be considered when selecting source material for cloning.

• Genetic diversity consideration: The high karyotype variation observed among P. tritici-repentis isolates (29 different karyotypes identified among 47 isolates) suggests potential sequence variation in the PTRG_11203 gene itself. When designing primers for amplification or synthetic gene constructs, consider analyzing sequences from multiple isolates to identify conserved regions and potential polymorphisms.

• Endogenous expression patterns: In its native context, PTRG_11203 expression may be regulated in response to environmental or developmental cues. Understanding these patterns can inform heterologous expression strategies, particularly if the goal is to produce enzyme variants with specific activity profiles.

Implementing these considerations will help develop an expression strategy that accounts for the unique genomic context of PTRG_11203 and maximizes the production of functional recombinant enzyme.

What purification workflow yields the highest purity and specific activity for Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase?

A systematic purification workflow for obtaining high-purity, high-activity Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase involves multiple chromatographic steps optimized for this particular enzyme. The recommended procedure is as follows:

• Cell lysis and crude extract preparation: Harvest E. coli cells expressing the His-tagged enzyme after optimal induction (0.5 mM IPTG, 6 hours, 30°C in TB medium) . Resuspend cells in lysis buffer (50 mM Tris-HCl pH 8.0, 300 mM NaCl, 10 mM imidazole, 1 mM PMSF, 5 mM β-mercaptoethanol) and disrupt using sonication (10 cycles of 30-second pulses with 30-second cooling periods) or high-pressure homogenization. Clarify the lysate by centrifugation at 15,000 × g for 30 minutes at 4°C.

• Immobilized Metal Affinity Chromatography (IMAC): Apply the clarified lysate to a Ni-NTA column pre-equilibrated with binding buffer (50 mM Tris-HCl pH 8.0, 300 mM NaCl, 10 mM imidazole). Wash extensively with washing buffer (same as binding buffer but with 20-40 mM imidazole) to remove non-specifically bound proteins. Elute the target enzyme with elution buffer (50 mM Tris-HCl pH 8.0, 300 mM NaCl, 250 mM imidazole) in a step gradient or linear gradient format.

• Buffer exchange: To remove imidazole, which can affect enzyme activity, perform buffer exchange using dialysis or gel filtration into a storage buffer (50 mM Tris-HCl pH 8.0, 150 mM NaCl, 10% glycerol, 1 mM DTT).

• Size Exclusion Chromatography (SEC): Apply the buffer-exchanged protein to a Superdex 200 column to separate any aggregates or impurities based on molecular size, using the storage buffer as the mobile phase.

• Purity assessment: Analyze the purified enzyme by SDS-PAGE, aiming for >90% purity . Western blotting using anti-His antibodies can confirm the identity of the target protein.

• Activity measurement: Determine the specific activity of the purified enzyme using a spectrophotometric assay measuring NADPH oxidation at 340 nm. The specific activity should be monitored throughout the purification process to calculate yield and purification fold.

Expected purification results:

This multi-step purification workflow typically yields enzyme with >90% purity and preserved catalytic activity, suitable for detailed biochemical and structural studies.

How can enzyme stability be enhanced during the purification and storage of Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase?

Enhancing the stability of Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase during purification and storage requires a systematic approach addressing multiple factors that contribute to protein denaturation and activity loss. Implement the following methodological strategies:

• Buffer composition optimization: Develop a stability-enhanced buffer system through systematic screening. Test various buffer compositions using a thermal shift assay (differential scanning fluorimetry) to identify formulations that increase the melting temperature (Tm) of the enzyme. A recommended screening matrix includes:

• Protease inhibitor strategy: Include a cocktail of protease inhibitors during purification, particularly PMSF (1 mM), EDTA (1 mM), and a commercial protease inhibitor mix. For long-term storage, these can be reduced to minimize potential interference with enzyme activity.

• Temperature management: Maintain strict temperature control during all purification steps, keeping the protein below 4°C. Use pre-chilled buffers and equipment. For column chromatography, consider using jacketed columns connected to a refrigerated circulator.

• Lyophilization protocol: For extended storage, lyophilization (freeze-drying) with protective excipients provides excellent stability. Formulate the enzyme in a buffer containing 6% trehalose and 1% sucrose as cryoprotectants before lyophilization . This preparation can be stored at -20°C/-80°C for extended periods.

• Aliquoting strategy: After purification, immediately divide the enzyme preparation into single-use aliquots to avoid repeated freeze-thaw cycles . Each freeze-thaw event typically results in a 10-15% reduction in activity.

• Storage format optimization: Compare activity retention in different storage formats:

• Reconstitution protocol: For lyophilized enzyme, develop a standardized reconstitution protocol using deionized sterile water to achieve 0.1-1.0 mg/mL protein concentration . After reconstitution, add glycerol to 50% final concentration for any samples intended for freezing.

These comprehensive strategies should maintain enzyme stability throughout purification and provide extended shelf-life during storage, preserving catalytic activity for experimental applications.

What are the optimal conditions for measuring the kinetic parameters of Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase?

The accurate determination of kinetic parameters for Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase requires carefully optimized assay conditions. The following methodological approach provides a systematic framework for establishing reliable enzyme kinetics measurements:

• Assay buffer composition: Use a buffer system that maintains optimal pH stability while not interfering with the spectrophotometric measurements. The recommended starting buffer is 100 mM potassium phosphate pH 7.5, containing 1 mM EDTA and 1 mM DTT. Perform a pH profile analysis by measuring activity across the range of pH 6.0-9.0 to determine the pH optimum for subsequent kinetic studies .

• Temperature optimization: Conduct initial rate measurements at 25°C, 30°C, and 37°C to determine temperature effects on activity. While higher temperatures typically yield higher activities, they may also accelerate enzyme denaturation. For most detailed kinetic studies, 30°C provides a good balance between activity and stability .

• Spectrophotometric assay setup: Monitor NADPH oxidation at 340 nm (ε = 6,220 M⁻¹cm⁻¹) using a UV-visible spectrophotometer with temperature control. Prepare reaction mixtures in a total volume of 1 mL containing:

  • Assay buffer (as determined above)

  • 0.1-0.2 μM purified enzyme

  • 200 μM NADPH (saturating concentration)

  • Variable concentrations of 3-ketoacyl-CoA substrate (ranging from 0.1 × Km to 10 × Km)

• Substrate preparation: Prepare a stock solution of 3-ketoacyl-CoA substrate in water or buffer and determine its concentration spectrophotometrically. Prepare a dilution series covering at least 8 different substrate concentrations spanning the range from well below to well above the anticipated Km value.

• Initiation and measurement protocol: Pre-incubate all components except enzyme at the assay temperature for 5 minutes. Initiate the reaction by adding enzyme and immediately begin monitoring A340 decrease. Collect initial rate data for 2-3 minutes or until approximately 10% of substrate is consumed.

• Data analysis: Calculate initial velocities from the linear portion of progress curves. Plot velocities versus substrate concentration and fit the data to the Michaelis-Menten equation using non-linear regression software:

$v = \frac{V_{max} \times [S]}{K_m + [S]}$

Extract Vmax and Km parameters from the fitted curve . Calculate kcat by dividing Vmax by the enzyme concentration.

• Validation controls: Include no-enzyme and no-substrate controls in each experiment. Verify linearity of the reaction with respect to enzyme concentration and time.

Expected kinetic parameters for Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase may fall within these ranges:

These optimized conditions will ensure reliable determination of kinetic parameters essential for understanding the catalytic properties of the enzyme.

What approaches can be used to investigate the structure-function relationship of Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase?

Investigating the structure-function relationship of Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase requires an integrated approach combining structural biology techniques with functional assays. The following methodological framework provides a comprehensive strategy:

• Sequence analysis and structural prediction: Perform detailed bioinformatic analysis of the 341-amino acid sequence using tools such as BLAST, Pfam, and PROSITE to identify conserved domains, catalytic residues, and structural motifs characteristic of the short-chain dehydrogenase/reductase (SDR) family. Use homology modeling software (SWISS-MODEL, I-TASSER) to generate a predicted 3D structure based on related enzymes with solved structures.

• Site-directed mutagenesis: Design a systematic mutagenesis strategy targeting key residues identified from sequence analysis and structural predictions. Focus on:

  • Catalytic triad/tetrad residues (likely including a conserved YXXXK motif)

  • Cofactor binding residues (within the N-terminal Rossmann fold)

  • Substrate binding pocket residues

  • Interface residues if oligomerization is predicted

Create single-point mutants using overlap extension PCR or commercial site-directed mutagenesis kits, express and purify each mutant, then characterize their kinetic parameters compared to the wild-type enzyme.

• X-ray crystallography: For definitive structural characterization, pursue X-ray crystallography through the following steps:

  • Screen crystallization conditions using commercial sparse matrix screens

  • Optimize promising conditions by varying precipitant concentration, pH, temperature

  • Consider crystallization both in apo form and with bound cofactor (NADPH)

  • Collect diffraction data at a synchrotron facility

  • Solve the structure by molecular replacement using related SDR structures

  • Refine the structure to resolution ideally better than 2.5 Å

• Hydrogen-deuterium exchange mass spectrometry (HDX-MS): Apply HDX-MS to probe protein dynamics and ligand-induced conformational changes:

  • Compare deuterium uptake patterns in free enzyme versus enzyme-cofactor and enzyme-substrate complexes

  • Identify regions with altered solvent accessibility upon ligand binding

  • Map these regions onto the structural model

• Thermal shift assays: Use differential scanning fluorimetry to assess protein stability:

  • Determine melting temperature (Tm) of wild-type and mutant proteins

  • Examine Tm shifts upon addition of cofactors and substrates

  • Correlate stability changes with catalytic efficiency

• Substrate specificity profiling: Systematically evaluate activity with a panel of different chain length 3-ketoacyl-CoA substrates (C4-C18) to generate a substrate specificity profile. Calculate kinetic efficiency (kcat/Km) for each substrate and correlate with structural features of the substrate-binding pocket.

The integration of these structural and functional approaches will yield a comprehensive understanding of key structure-function relationships in Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase, potentially revealing:

This multi-faceted approach provides rigorous characterization of structure-function relationships essential for understanding this enzyme's role in fungal metabolism.

How does Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase compare structurally and functionally to homologous enzymes from other organisms?

• Sequence homology analysis: A comprehensive BLAST analysis of the 341-amino acid sequence of Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase reveals significant homology with related enzymes across various taxonomic groups. The table below summarizes key homology relationships:

• Inhibitor sensitivity profile: Comparative analysis of inhibitor sensitivity can further differentiate the P. tritici-repentis enzyme from homologs. Fungal 3-ketoacyl-CoA reductases typically show distinct inhibition patterns compared to bacterial and mammalian counterparts, providing potential targets for selective inhibition.

This comprehensive comparison highlights both the evolutionary conservation of core catalytic mechanisms and the specialization that likely enables P. tritici-repentis 3-ketoacyl-CoA reductase to fulfill specific metabolic roles in fungal physiology, particularly in relation to pathogenicity and adaptation to the plant host environment.

What potential applications exist for Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase in understanding wheat tan spot disease mechanisms?

Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase offers significant potential for advancing our understanding of wheat tan spot disease mechanisms through multiple research applications. This enzyme's role in fungal fatty acid metabolism provides unique insights into pathogen biology and potential intervention strategies.

• Metabolic pathway analysis in pathogenesis: As 3-ketoacyl-CoA reductase (KAR) plays a central role in fatty acid biosynthesis, studying its activity can reveal how P. tritici-repentis modulates its lipid metabolism during different stages of infection. Specific research applications include:

  • Comparing enzyme activity and expression levels between saprophytic growth and plant infection phases

  • Tracing carbon flux through fatty acid biosynthesis pathways during host colonization

  • Determining if specialized lipid structures required for appressorium formation and penetration depend on this enzyme

• Gene knockout/knockdown studies: Using CRISPR-Cas9 or RNAi techniques to disrupt or downregulate PTRG_11203 expression, researchers can evaluate:

  • Effects on fungal growth, morphology, and cell wall integrity

  • Impact on virulence and pathogenicity in wheat infection assays

  • Potential metabolic bottlenecks or compensatory pathways activated in response

• Inhibitor development and screening: The recombinant enzyme serves as an excellent target for developing specific inhibitors that could lead to novel fungicides:

  • High-throughput screening of chemical libraries against purified recombinant enzyme

  • Structure-based drug design utilizing the enzyme's structural model

  • Validation of hit compounds in whole-cell fungal assays and plant infection models

• Comparative genomics across isolates: The high genome plasticity observed in P. tritici-repentis (with 29 different karyotypes identified among 47 isolates) suggests potential genetic diversity in metabolic enzymes. The recombinant enzyme enables:

  • Sequence and activity comparisons among different races and isolates

  • Correlation of enzyme variants with virulence phenotypes

  • Identification of selective pressures acting on this metabolic pathway

• Biomarker development: The enzyme or its metabolic products could serve as biomarkers for:

  • Early detection of tan spot infection in wheat

  • Monitoring fungicide resistance development

  • Distinguishing P. tritici-repentis from other wheat pathogens in mixed infections

• Systems biology integration: Incorporating knowledge about 3-ketoacyl-CoA reductase into broader metabolic networks provides:

  • Comprehensive mapping of lipid metabolism during infection

  • Integration with transcriptomic and proteomic data to understand regulatory networks

  • Predictive models of fungal adaptation to environmental stresses and host defenses

• Host-pathogen interaction studies: The enzyme's products may directly or indirectly influence host responses:

  Research Question	Experimental Approach	Expected Outcome
  Do fungal lipids derived from this pathway act as PAMPs?	Treat wheat cells with purified lipids, measure defense responses	Identification of novel pathogen recognition mechanisms
  Can wheat produce inhibitors of fungal KAR?	Screen wheat metabolites for enzyme inhibition	Discovery of natural defense compounds
  Does the enzyme contribute to effector production/delivery?	Compare effector secretion in wildtype vs. KAR mutants	Understanding of effector biology

These diverse research applications demonstrate how Recombinant Pyrenophora tritici-repentis 3-ketoacyl-CoA reductase serves as both a valuable research tool and a potential target for intervention strategies aimed at controlling wheat tan spot disease. By integrating molecular, biochemical, and systems approaches, researchers can leverage this enzyme to develop more effective and sustainable management strategies for this economically important wheat disease.