Recombinant Escherichia coli Putative protein-disulfide oxidoreductase (UTI89_C3475)

What is the function of putative protein-disulfide oxidoreductase in E. coli UTI89?

Putative protein-disulfide oxidoreductase in E. coli UTI89 is likely part of the disulfide bond formation machinery, which is critical for protein stability and function. Similar to characterized protein disulfide oxidoreductases (PDOs), UTI89_C3475 likely catalyzes the formation, reduction, and isomerization of disulfide bonds in target proteins within the bacterial periplasm . The enzyme typically contains active site CXXC motifs that mediate electron transfer during disulfide bond formation or rearrangement . In pathogenic E. coli strains like UTI89, proper disulfide bond formation is essential for the folding and function of virulence factors and other secreted or membrane proteins .

How does UTI89_C3475 compare to other protein disulfide oxidoreductases?

UTI89_C3475, as a putative protein disulfide oxidoreductase, likely shares structural similarities with other characterized PDOs. Typical PDOs contain two thioredoxin-related domains arranged in a tandem-like manner to form a closed protein domain . Each domain typically contains a CXXC active site motif with distinct redox properties . While specific data on UTI89_C3475 is limited in the provided search results, it likely functions within the disulfide bond formation pathway similar to DsbA, DsbB, DsbC, and DsbD in E. coli, which together catalyze the introduction and isomerization of disulfide bonds in periplasmic and secreted proteins . The enzyme's structure likely features substrate-binding grooves formed by residues surrounding the active sites .

What are the typical growth conditions for E. coli UTI89 expressing recombinant proteins?

E. coli UTI89, being a clinical isolate, may require different growth conditions compared to laboratory strains like E. coli K-12 for optimal recombinant protein expression . For successful recombinant protein expression, UTI89 is typically grown in rich media such as LB (Luria-Bertani) broth at 37°C with appropriate antibiotic selection based on the expression vector used . Growth temperature may be adjusted to 18-30°C after induction to enhance soluble protein expression . The specific growth conditions should be optimized based on the properties of the target protein, with consideration for factors such as oxygen availability, media composition, and induction parameters that affect disulfide bond formation capacity .

What expression systems are suitable for recombinant production of UTI89_C3475?

For recombinant production of putative protein-disulfide oxidoreductase from UTI89, the pET expression system featuring the T7 promoter is often the first choice due to its strong promoter activity and widespread use for heterologous protein expression in E. coli . Alternative expression systems may include vectors with the Arabinose promoter, which exhibits lower basal transcriptional activity, or hybrid promoters such as trc and tac, though these may show leaky expression . The selection of an appropriate expression system should consider factors such as the desired expression level, timing of induction, and potential toxicity of the target protein . For disulfide-bonded proteins like oxidoreductases, specialized expression strains such as Origami, SHuffle, or CyDisCo may enhance correct disulfide bond formation .

How can I clone the UTI89_C3475 gene from E. coli UTI89?

To clone the UTI89_C3475 gene from E. coli UTI89, employ the modified Red recombinase-based gene targeting method with extended homology regions. This approach has been successfully used for genetic manipulation of recalcitrant E. coli isolates like UTI89 . Begin by designing PCR primers that include 500-600 bp homology regions flanking the UTI89_C3475 gene, as these longer homology regions significantly improve recombination efficiency compared to the standard 50 bp regions used in K-12 strains . Extract genomic DNA from E. coli UTI89 using a commercial kit or standard phenol-chloroform extraction methods. Amplify the target gene using high-fidelity PCR, then clone it into an appropriate expression vector such as pET, ensuring in-frame fusion with purification tags . Verify the construct by sequencing before transformation into expression hosts.

What expression conditions maximize the soluble yield of recombinant UTI89_C3475?

To maximize soluble yield of recombinant UTI89_C3475, implement a systematic optimization of expression conditions. First, select an appropriate E. coli expression strain such as BL21(DE3) or Origami for enhanced disulfide bond formation . Test multiple induction parameters using the following matrix approach:

For optimal expression of disulfide-containing proteins like UTI89_C3475, consider co-expression with helper proteins such as DsbC isomerase or thioredoxin reductase to facilitate proper folding . Monitor protein expression by SDS-PAGE analysis of both soluble and insoluble fractions at different time points to determine optimal harvest time .

What purification strategy is recommended for UTI89_C3475?

A multi-step purification strategy is recommended for obtaining high-purity UTI89_C3475. Begin with immobilized metal affinity chromatography (IMAC) using a His-tag fusion, which provides efficient initial capture of the target protein . The purification protocol should include:

• Cell lysis in buffer containing 50 mM Tris-HCl pH 8.0, 300 mM NaCl, 10 mM imidazole, and protease inhibitors

• IMAC purification with gradient elution (20-250 mM imidazole)

• Tag removal using specific proteases if the tag affects functional studies

• Size exclusion chromatography to achieve >95% purity and remove aggregates

• Ion exchange chromatography as a polishing step

For optimal results, maintain reducing conditions (1-5 mM DTT or 2-5 mM β-mercaptoethanol) during purification to prevent non-specific disulfide bond formation while preserving the native CXXC active sites . If the protein demonstrates instability, consider adding glycerol (10-20%) and specific metal ions or cofactors that may enhance stability . The purified protein should be stored in small aliquots at -80°C in buffer containing stabilizing agents to maintain enzymatic activity.

How can I assess the disulfide oxidoreductase activity of UTI89_C3475?

To assess the disulfide oxidoreductase activity of UTI89_C3475, implement multiple complementary assays that evaluate different aspects of its function. The insulin reduction assay is a standard method, where the reduction of insulin disulfide bonds causes precipitation that can be monitored spectrophotometrically at 650 nm . For oxidative activity assessment, monitor the oxidation of reduced RNase A followed by enzyme reactivation assays . Additionally, use fluorescent peptide substrates containing appropriate CXXC motifs to measure real-time kinetics of disulfide exchange reactions.

Comparative enzyme kinetics can be derived using the following equation:

$v = \frac{k_{cat} \times [E] \times [S]}{K_m + [S]}$

where v is the reaction velocity, k_cat is the catalytic constant, [E] is enzyme concentration, [S] is substrate concentration, and K_m is the Michaelis constant .

For more accurate determination of redox potential, employ protein-film voltammetry or redox equilibrium experiments with glutathione to calculate the standard redox potential (E°') of the active site disulfides . These data will provide insights into the catalytic mechanism and substrate specificity of UTI89_C3475.

How do mutations in the CXXC motifs affect the function of UTI89_C3475?

Mutations in the CXXC motifs significantly alter the function of protein disulfide oxidoreductases like UTI89_C3475, with effects varying based on the specific residues changed. Site-directed mutagenesis studies of PDOs have shown that substituting either cysteine in the CXXC motif abolishes catalytic activity, while modifying the XX residues alters the redox potential and substrate specificity . The XX residues influence the conformational stability and pKa values of the active site cysteines, thereby determining whether the enzyme functions predominantly as an oxidase, reductase, or isomerase .

In UTI89_C3475, which likely contains two CXXC motifs with different redox properties, the differential behavior of these sites creates functional asymmetry that enables sequential reactions in disulfide shuffling (reduction followed by oxidation) . Mutation of the N-terminal CXXC motif typically affects oxidative activity more severely, while changes to the C-terminal motif primarily impact isomerase function . Kinetic analysis of mutants reveals that substituting the intervening XX residues with more hydrophobic amino acids generally shifts the redox potential to more oxidizing values, enhancing oxidase activity at the expense of isomerase function .

What is the relationship between UTI89_C3475 activity and E. coli UTI89 virulence?

The relationship between UTI89_C3475 activity and E. coli UTI89 virulence is likely significant but complex. As a putative protein-disulfide oxidoreductase, UTI89_C3475 presumably participates in the folding of secreted virulence factors that require disulfide bonds for stability and function . In uropathogenic E. coli like UTI89, numerous virulence factors including adhesins, toxins, and secretion system components contain disulfide bonds that are essential for their activity .

Studies of disulfide oxidoreductases in pathogenic bacteria demonstrate that disruption of disulfide bond formation pathways typically results in attenuated virulence due to misfolding of key virulence proteins . For instance, type 1 fimbriae, which are critical for UTI89 colonization and pathogenesis, contain subunits with essential disulfide bonds . Given that UTI89_C3475 likely functions within the disulfide formation machinery, gene deletion or active site mutations would be expected to impair the assembly of these structures and reduce virulence in infection models .

A comprehensive analysis using the modified Red recombinase system to generate UTI89_C3475 deletion mutants, followed by phenotypic characterization in various virulence assays (adhesion, invasion, biofilm formation) and in vivo infection models, would elucidate the specific contributions of this oxidoreductase to pathogenesis .

How does the redox environment in E. coli affect UTI89_C3475 function?

The redox environment in E. coli significantly influences the function of disulfide oxidoreductases like UTI89_C3475 through multiple mechanisms. In the periplasm, where disulfide bond formation naturally occurs, the redox potential is maintained in an oxidizing state (approximately -165 mV) by the DsbA/DsbB system, while the cytoplasm maintains a reducing environment (approximately -270 mV) through the glutathione/glutaredoxin and thioredoxin systems . The activity of UTI89_C3475 is intrinsically linked to these compartment-specific redox conditions.

Under different growth conditions, the cellular requirement for disulfide-bonded proteins changes significantly, altering the demand on the oxidative folding machinery . In rapidly growing cells, most oxidative folding capacity is dedicated to maintaining the proteome, while cells in nutrient-limited conditions (like chemostats) appear constrained by their disulfide isomerization capabilities . Environmental stressors, including oxidative stress, pH changes, and nutrient limitation, can shift cellular redox balance and consequently affect UTI89_C3475 function .

The catalytic efficiency of UTI89_C3475 would be optimized for its natural redox environment, with its activity modulated by the relative concentrations of oxidized and reduced substrates, as well as by interactions with redox partner proteins that mediate electron transfer . These complex interactions could be quantitatively modeled using differential equations to predict how changing redox conditions affect disulfide bond formation rates in the bacterial proteome .

What structural features determine the substrate specificity of UTI89_C3475?

The substrate specificity of UTI89_C3475, like other protein disulfide oxidoreductases, is likely determined by multiple structural features beyond the catalytic CXXC motifs. Based on structural studies of related PDOs, key determinants include:

• Surface grooves formed by residues surrounding the active sites, which constitute the substrate binding regions and determine accessibility for different protein substrates

• The electrostatic potential map of these binding grooves, which facilitates specific interactions with charged regions of substrate proteins

• Hydrophobic patches that participate in non-covalent interactions with substrate proteins prior to disulfide exchange

• The distance and spatial orientation between the two CXXC active sites, which influences the ability to recognize and isomerize incorrectly formed disulfide bonds

The neighborhood of the two active sites likely creates a functional asymmetry that enables sequential redox reactions, with one site specialized for substrate binding and initial disulfide exchange, while the other site mediates subsequent rearrangements . The substrate-binding model derived from crystal packing contacts of PDO enzymes suggests that peptide substrates bind in an extended conformation along surface grooves, with specific hydrogen bonding patterns determining the orientation and positioning of substrate cysteine residues relative to the catalytic cysteines .

Comparative structural analysis with other characterized PDOs would reveal conserved features that determine common substrate recognition mechanisms versus specialized regions that confer specificity to UTI89_C3475.

Why is my recombinant UTI89_C3475 forming inclusion bodies and how can I prevent this?

Recombinant UTI89_C3475 may form inclusion bodies due to multiple factors related to its expression as a disulfide-containing protein. The rapid production rate in high-level expression systems can overwhelm the cell's folding machinery, leading to protein aggregation . Additionally, expressing a periplasmic protein like UTI89_C3475 in the reducing environment of the cytoplasm may prevent proper disulfide bond formation, contributing to misfolding .

To prevent inclusion body formation:

• Reduce expression rate by lowering inducer concentration (0.1-0.2 mM IPTG instead of 1 mM) and decreasing growth temperature to 16-20°C during induction

• Use specialized E. coli strains with oxidizing cytoplasm such as Origami, SHuffle, or CyDisCo that facilitate disulfide bond formation in the cytoplasm

• Co-express chaperones and folding modulators such as DsbC, which has been shown to enhance soluble expression of disulfide-bonded proteins

• Direct the protein to the periplasm using appropriate signal sequences, where the native disulfide formation machinery operates

• Modify buffer conditions by adding stabilizing agents like glycerol (10%), low concentrations of non-denaturing detergents, or specific metal ions that may enhance stability

• Optimize codon usage for E. coli, particularly in the 5'UTR and N-terminal codons, which significantly impact translation efficiency and protein folding

If inclusion bodies persist despite these optimizations, consider developing a refolding protocol from solubilized inclusion bodies using controlled oxidative refolding conditions with appropriate redox buffer systems (e.g., different ratios of reduced/oxidized glutathione) .

How can I improve the stability of purified UTI89_C3475 during storage?

Improving the stability of purified UTI89_C3475 requires careful attention to buffer composition and storage conditions, especially given its redox-active nature. To enhance stability:

• Optimize buffer composition:

  • Use 50 mM Tris-HCl or phosphate buffer at pH 7.5-8.0

  • Include 100-150 mM NaCl to maintain ionic strength

  • Add 10-20% glycerol as a cryoprotectant

  • Include 1-5 mM of reducing agent (DTT or TCEP) to prevent non-specific oxidation

  • Consider adding 0.1 mM EDTA to prevent metal-catalyzed oxidation

• Storage recommendations:

  • Concentrate protein to 1-5 mg/ml (avoiding excessive concentration)

  • Flash-freeze small aliquots (50-100 μl) in liquid nitrogen

  • Store at -80°C rather than -20°C to minimize freeze-thaw damage

  • Avoid repeated freeze-thaw cycles by preparing single-use aliquots

• Stability assessment protocol:

  • Monitor activity retention over time using standardized assays

  • Analyze sample by analytical size exclusion chromatography to detect aggregation

  • Use differential scanning fluorimetry to determine thermal stability in different buffer conditions

For critical applications requiring extended stability periods, consider protein lyophilization in the presence of appropriate cryoprotectants like trehalose or sucrose (5-10%) . Alternatively, immobilization on appropriate resin or support materials can significantly enhance storage stability while potentially allowing for reuse in enzymatic applications .

What strategies can resolve heterogeneity in my UTI89_C3475 preparation?

Heterogeneity in UTI89_C3475 preparations may arise from multiple factors including incomplete disulfide bond formation, proteolytic degradation, and post-translational modifications. To resolve these issues:

• Disulfide heterogeneity:

  • Analyze redox state using non-reducing SDS-PAGE with mobility shift assays

  • Apply controlled oxidation using glutathione redox buffer (2 mM GSSG/8 mM GSH) overnight at 4°C

  • Separate different redox forms using thiol-specific chromatography (e.g., ThioBond resin)

• Size heterogeneity:

  • Apply rigorous size exclusion chromatography with narrow fractionation ranges

  • Consider high-resolution techniques like analytical ultracentrifugation to characterize and separate oligomeric species

  • Use dynamic light scattering to monitor sample homogeneity before and after purification steps

• Charge heterogeneity:

  • Employ ion exchange chromatography with shallow gradients to separate differently charged species

  • Consider isoelectric focusing if charge variants are problematic

  • Analyze by mass spectrometry to identify specific modifications causing charge variation

• Process optimization:

  • Add protease inhibitors throughout purification to prevent degradation

  • Implement rigorous quality control using activity assays correlated with homogeneity metrics

  • Consider point mutations of surface-exposed cysteines not involved in catalysis to prevent non-specific disulfide formation

The specific preparation challenges for UTI89_C3475 would likely include maintaining the correct redox state of the CXXC active sites while preventing non-specific disulfide formation . A systematic approach involving analytical characterization after each purification step will help identify the sources of heterogeneity and guide optimization efforts.

How can I troubleshoot low expression yields of UTI89_C3475?

Low expression yields of UTI89_C3475 could stem from multiple factors including codon usage, mRNA folding, protein toxicity, or strain compatibility. To systematically troubleshoot and improve yields:

• Transcription-level optimization:

  • Test different promoters beyond T7, such as Arabinose promoter for tighter control

  • Analyze expression kinetics at different time points post-induction

  • Consider using different E. coli strains with varying RNA polymerase levels

• Translation-level optimization:

  • Analyze and optimize the 5'UTR and N-terminal codons, which significantly impact translation efficiency

  • Redesign the ribosome binding site to optimize translation initiation

  • Consider synonymous codon changes in the first 15-25 codons to reduce mRNA secondary structure

• Host strain considerations:

  • Test expression in different E. coli strains beyond common BL21(DE3) derivatives

  • For recalcitrant strains like UTI89, specialized genetic manipulation methods may be needed

  • Consider strain-specific factors that may affect oxidoreductase expression

• Systematic expression testing:

  • Implement a small-scale expression screen with the following variables:

If toxicity is suspected, consider using tightly regulated expression systems like the Arabinose promoter, which exhibits minimal basal transcriptional activity . For disulfide-containing proteins like UTI89_C3475, expression capacity may be limited by the cell's oxidative folding machinery, which varies with growth conditions . Quantitative measurement of expression levels using Western blotting rather than simply assessing presence/absence can help identify optimal conditions.

How do I analyze and interpret kinetic data for UTI89_C3475 enzymatic activity?

To properly analyze and interpret kinetic data for UTI89_C3475 enzymatic activity, implement a systematic approach that accounts for the complexity of disulfide exchange reactions. Begin by establishing a standardized assay measuring either the oxidation of reduced substrates or the isomerization of misfolded disulfide bonds .

For steady-state kinetics, collect initial velocity data at varying substrate concentrations and fit to appropriate models. While the Michaelis-Menten equation is commonly used for simple enzymes, disulfide oxidoreductases often exhibit more complex behaviors:

$v = \frac{k_{cat} \times [E] \times [S]}{K_m + [S]}$

For complex kinetic behaviors, consider using more sophisticated models that account for:

• Multiple substrates and products in ping-pong mechanisms

• Substrate inhibition at high concentrations

• Cooperativity between multiple active sites

The redox potential of UTI89_C3475 active sites can be determined using the Nernst equation:

$E = E°' - \frac{RT}{nF} \ln\frac{[\text{reduced}]}{[\text{oxidized}]}$

where E°' is the standard redox potential, R is the gas constant, T is temperature, n is the number of electrons transferred, and F is Faraday's constant .

For data interpretation, compare kinetic parameters (kcat, Km, kcat/Km) across different substrates to assess substrate specificity. Create substrate specificity profiles based on relative activity, and correlate structural features of substrates with activity levels to develop structure-activity relationships . Remember that the physiological function of UTI89_C3475 may involve interactions with multiple partners in the disulfide formation pathway, so in vitro activity with model substrates provides only partial insights into its cellular role.

What techniques can be used to identify physiological substrates of UTI89_C3475?

Identifying the physiological substrates of UTI89_C3475 requires multiple complementary approaches that capture the dynamic interactions of this oxidoreductase in vivo. Several techniques can be employed:

• Proteomic trap approaches:

  • Generate a "substrate-trapping" mutant by replacing the resolving cysteine in one CXXC motif to create stable mixed disulfides with substrates

  • Perform immunoprecipitation followed by mass spectrometry to identify trapped proteins

  • Validate interactions using targeted approaches like Western blotting

• Comparative redox proteomics:

  • Compare the disulfide proteome of wild-type and UTI89_C3475 deletion mutants using techniques like OxICAT (isotope-coded affinity tags for oxidized cysteines)

  • Analyze changes in the oxidation state of specific proteins in the absence of UTI89_C3475

  • Quantify the impact on disulfide bond formation in various cellular compartments

• Protein-protein interaction screens:

  • Bacterial two-hybrid systems adapted for oxidoreductase interactions

  • Crosslinking approaches using photo-activatable amino acids incorporated at the active site

  • Proximity labeling methods such as APEX2 fusion to UTI89_C3475 to biotinylate proximal proteins

• Functional genomics approaches:

  • Transcriptomic analysis to identify genes co-regulated with UTI89_C3475

  • Synthetic genetic array to identify genetic interactions that enhance or suppress phenotypes of UTI89_C3475 deletion

  • Phenotypic screening of UTI89_C3475 deletion in various stress conditions to identify functional pathways

These approaches should be integrated with quantitative modeling of the bacterial disulfide proteome, which would allow prediction of which proteins are most likely to require UTI89_C3475 for proper folding based on their disulfide content and folding kinetics .

How can UTI89_C3475 be used as a tool for enhancing recombinant protein production?

UTI89_C3475, as a putative protein-disulfide oxidoreductase, has significant potential as a tool for enhancing recombinant protein production, particularly for disulfide-rich proteins that are challenging to express in bacterial systems. Several strategic applications include:

• Co-expression approaches:

  • Clone UTI89_C3475 into a compatible expression vector for co-expression with target disulfide-bonded proteins

  • Design dual-expression systems with tunable ratios of oxidoreductase to target protein

  • Create fusion proteins where UTI89_C3475 is linked to the target protein via a cleavable linker

• Engineered expression hosts:

  • Develop specialized E. coli strains with genomic integration of UTI89_C3475 under regulated promoters

  • Balance expression levels to optimize the oxidative folding capacity of the cell

  • Combine with other folding modulators like chaperones for synergistic effects

• In vitro applications:

  • Use purified UTI89_C3475 for in vitro refolding of inclusion body proteins

  • Develop immobilized UTI89_C3475 refolding columns for continuous processing

  • Create optimized redox buffer systems containing UTI89_C3475 for higher refolding yields

• Synthetic biology approaches:

  • Design synthetic oxidative folding pathways incorporating UTI89_C3475 with complementary enzymes

  • Engineer compartmentalized expression systems that mimic the natural separation of reducing and oxidizing environments

  • Create feedback-regulated expression systems that adjust oxidoreductase levels based on protein production demands

When implementing these strategies, it's important to consider that the cell's oxidative folding machinery has finite capacity, and cells must balance the requirements of the native proteome with those of recombinant proteins . Quantitative modeling of disulfide bond formation kinetics can help predict the optimal ratio of oxidoreductase to target protein and identify potential bottlenecks in the folding pathway .

What evolutionary insights can be gained from studying UTI89_C3475 in pathogenic E. coli?

Studying UTI89_C3475 in pathogenic E. coli provides valuable evolutionary insights into bacterial adaptation, virulence mechanisms, and protein folding systems. Several key aspects to investigate include:

• Evolutionary conservation and divergence:

  • Comparative genomic analysis of UTI89_C3475 homologs across E. coli pathotypes and commensal strains

  • Phylogenetic analysis to trace the evolutionary history of protein disulfide oxidoreductases in Enterobacteriaceae

  • Identification of selective pressures acting on different domains or active site regions

• Pathoadaptive significance:

  • Analysis of sequence variation in UTI89_C3475 between uropathogenic E. coli strains and other pathotypes

  • Correlation between specific UTI89_C3475 variants and virulence phenotypes

  • Investigation of horizontal gene transfer events that may have shaped oxidoreductase evolution

• Functional specialization:

  • Comparison with oxidoreductases from non-pathogenic E. coli to identify pathogen-specific features

  • Analysis of substrate specificity differences that may reflect adaptation to virulence factor folding

  • Investigation of unique structural or catalytic properties that support pathogen-specific protein folding needs

• Co-evolutionary relationships:

  • Analysis of co-evolution between UTI89_C3475 and its substrate proteins

  • Identification of coordinated evolutionary changes in the oxidative folding machinery

  • Investigation of how oxidoreductase evolution correlates with acquisition of virulence factors

The study of UTI89_C3475 may reveal how pathogenic E. coli have adapted their protein folding machinery to support the production of virulence factors, many of which contain disulfide bonds essential for their stability and function . Understanding these evolutionary adaptations could provide insights into both bacterial pathogenesis mechanisms and fundamental principles of protein folding and quality control systems across diverse organisms.

What are the future research directions for UTI89_C3475?

Future research on UTI89_C3475 should focus on elucidating its precise role in E. coli UTI89 physiology and pathogenesis, as well as exploring its biotechnological applications. Priority research directions include comprehensive structural characterization using X-ray crystallography or cryo-EM to reveal substrate binding modes and catalytic mechanisms . Developing in vivo activity assays to monitor UTI89_C3475 function in real-time during infection processes would provide insights into its dynamic roles in pathogenesis .

Systems biology approaches integrating transcriptomics, proteomics, and metabolomics data could map the entire network of UTI89_C3475 interactions under different environmental conditions . Engineering UTI89_C3475 variants with enhanced stability or modified substrate specificity through directed evolution or rational design could yield valuable tools for biotechnology applications . Additionally, exploring UTI89_C3475 as a potential drug target for developing novel antimicrobials against uropathogenic E. coli would address the growing need for alternative therapeutic strategies .