Recombinant Escherichia coli O7:K1 Universal stress protein B (uspB)

What is the structural characterization of E. coli O7:K1 Universal stress protein B?

Recombinant E. coli O7:K1 Universal stress protein B (uspB) is a 111-amino acid membrane-associated protein with the sequence "MISTVALFWALCVVCIVNMARYFSSLRALLVVLRNCDPLLYQYVDGGGFFTSHGQPNKQVRLVWYIYAQRYRDHHDDEFIRRCERVRRQFILTSALCGLVVVSLIALMIWH" . The protein contains hydrophobic regions consistent with membrane localization, particularly at its N-terminal and C-terminal domains. When expressed recombinantly with an N-terminal His-tag, the protein is typically purified as a lyophilized powder with purity greater than 90% as determined by SDS-PAGE .

How does uspB fit within the broader Universal Stress Protein family in E. coli?

The Universal Stress Protein (USP) family in E. coli consists of several members including UspA, UspC (YecG), UspD (YiiT), UspE (YdaA), UspF (YnaF, UP03), and UspG (YbdQ) . These proteins have been divided into three subfamilies based on their sequence and functional characteristics. Additionally, E. coli USPs are categorized into two major classes and four minor subclasses . The uspB protein represents an additional member of this family that functions within the complex network of stress response mechanisms in E. coli, particularly in the context of membrane-associated stress responses based on its sequence characteristics.

What experimental approaches are recommended for expressing recombinant uspB?

For recombinant expression of uspB from E. coli O7:K1, the following methodology is recommended:

• Clone the full-length gene (positions 1-111) into an expression vector containing an N-terminal His-tag.

• Transform the construct into an E. coli expression strain suitable for membrane protein expression.

• Induce protein expression under optimal conditions (typically with IPTG for T7-based systems).

• Harvest cells and lyse using appropriate detergents that solubilize membrane proteins.

• Purify using Ni-NTA affinity chromatography, taking care to include detergents in all buffers.

• Consider reconstitution methods if functional studies are planned.

For storage, lyophilization in a Tris/PBS-based buffer with 6% trehalose (pH 8.0) has proven effective . Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL, adding 5-50% glycerol for long-term storage at -20°C/-80°C .

How can researchers investigate the relationship between uspB and K1 capsule formation in E. coli O7:K1?

To investigate potential relationships between uspB and K1 capsule formation, researchers should employ a multifaceted approach:

• Gene knockout studies: Create a uspB deletion mutant using λ-red recombineering or thermosensitive allelic replacement using the plasmid pKO3blue . Compare capsule expression between wild-type and mutant strains using flow cytometric analysis with rEndoNA2-GFP, which specifically targets polySia K1 capsule .

• Complementation experiments: Reintroduce uspB on a plasmid to confirm phenotype restoration.

• Serum resistance assays: Compare the susceptibility of wild-type and uspB mutant strains to complement C3b deposition and serum killing as described by Sarowska et al. , where bacteria are incubated in human serum and survival rates are quantified.

• Co-expression analyses: Examine expression patterns of uspB alongside known K1 capsule genes (such as those in the K1-cps locus) under various stress conditions.

• Protein-protein interaction studies: Use pull-down assays or bacterial two-hybrid systems to identify potential interactions between UspB and proteins involved in capsule biosynthesis.

What methodological approaches can resolve contradictions in uspB stress response data?

When confronting contradictory data regarding uspB's role in stress response:

• Standardize strain backgrounds: Ensure experiments use identical genetic backgrounds, as subtle strain differences can influence stress responses. Consider using both laboratory K-12 derivatives and clinically relevant O7:K1 strains.

• Define precise stress conditions: USPs respond differently to various stressors . Design experiments with precisely controlled stress parameters including:

  • Type of stress (oxidative, osmotic, pH, nutrient limitation)

  • Intensity of stress

  • Duration of exposure

  • Growth phase during stress application

• Use multiple readouts: Combine transcriptional analysis (RT-qPCR), protein expression monitoring (Western blot), and phenotypic assays (growth curves, survival rates).

• Time-course experiments: USP effects may be transient or growth phase-dependent. The phenotype of uspA deletion mutants becomes apparent only during transition to stationary phase after several generations of growth .

• Consider redundancy: Multiple USP proteins may have overlapping functions. Generate combinations of usp gene deletions to overcome functional redundancy .

• Environmental relevance: Test conditions mimicking natural habitats of E. coli O7:K1, such as human serum or cerebrospinal fluid.

How can the ATP-binding properties of uspB be characterized and compared to other USP family proteins?

To characterize ATP-binding properties of uspB and compare with other USP family members:

• Structural analysis:

  • Perform crystallography studies on purified uspB with and without ATP or analogs

  • Compare binding sites with known USP structures like E. coli USPE (PDB: 5CB0) and Arabidopsis At3g01520 (PDB: 2GM3)

• Binding assays:

  • Isothermal titration calorimetry (ITC) to determine binding constants

  • Fluorescence-based assays using ATP analogs like TNP-ATP

  • Filter binding assays with radiolabeled ATP

• Mutational analysis:

  • Identify potential ATP-binding residues by sequence alignment with known ATP-binding USPs

  • Generate point mutations in these residues

  • Test mutant proteins for altered ATP binding properties

• Functional correlation:

  • Assess how ATP binding affects uspB's role in stress response

  • Test uspB ATP-binding mutants for complementation of phenotypes in uspB deletion strains

• Comparative analysis:

  • Systematically compare ATP binding parameters (Kd, binding kinetics) across USP family members

  • Correlate binding differences with functional differences

What approaches should be used to investigate uspB's role in E. coli O7:K1 virulence in experimental infection models?

To investigate uspB's contribution to E. coli O7:K1 virulence:

• Generation of isogenic strains:

  • Create a precise uspB deletion mutant in E. coli O7:K1 using λ-red recombineering

  • Complement with wild-type uspB on a stable plasmid

  • Generate point mutations in specific functional domains of uspB

• In vitro virulence assays:

  • Serum resistance: Compare survival rates in human serum between wild-type and mutant strains

  • Adhesion and invasion: Quantify bacterial adherence to and invasion of relevant cell types (epithelial cells, endothelial cells)

  • Biofilm formation: Assess ability to form biofilms on abiotic surfaces

• Animal infection models:

  • Bacteremia model: Intravenous infection to assess persistence in bloodstream

  • Urinary tract infection model: Transurethral inoculation to assess colonization and ascending infection

  • Neonatal meningitis model: Appropriate for K1 strains which are associated with neonatal meningitis

• Immune response characterization:

  • Complement activation: Measure C3b deposition on bacterial surface using flow cytometry

  • Phagocytosis resistance: Determine survival within macrophages and neutrophils

  • Cytokine induction: Quantify pro-inflammatory cytokine production

• In vivo imaging:

  • Use bioluminescent or fluorescent reporter strains to track infection progression in real-time

How can researchers effectively analyze the regulation of uspB expression under different environmental conditions?

To comprehensively analyze uspB regulation:

• Transcriptional analysis:

  • Construct transcriptional fusions (uspB promoter-reporter) using systems like lacZ, GFP, or luciferase

  • Perform RT-qPCR under various conditions (stress conditions, growth phases)

  • Map transcription start sites using 5' RACE or primer extension

  • Identify transcription factor binding sites through ChIP-seq or DNA footprinting

• Stress condition testing matrix:

  • Carbon source limitation (glucose starvation)

  • Phosphate limitation

  • Oxidative stress (H2O2, superoxide generators)

  • Heat shock

  • DNA damage (mitomycin C, UV)

  • pH stress

  • Osmotic stress

  • Transition to stationary phase

• Regulatory network mapping:

  • Test uspB expression in strains lacking known stress regulators (rpoS, cysB)

  • Perform RNA-seq to identify co-regulated genes

  • Use transposon mutagenesis to identify novel regulators

• Post-transcriptional regulation:

  • Analyze mRNA stability under different conditions

  • Investigate potential small RNA regulators

  • Examine translational efficiency using ribosome profiling

• Comparative analysis:

  • Compare regulation patterns with other USP family members

  • Examine differences between laboratory K-12 and pathogenic O7:K1 strains

What techniques can determine the membrane topology and protein interactions of uspB in E. coli O7:K1?

To characterize uspB membrane topology and interaction partners:

• Membrane topology determination:

  • Construct fusion proteins with topology reporters (PhoA, LacZ, GFP)

  • Perform cysteine accessibility methods with membrane-impermeable reagents

  • Use protease protection assays

  • Apply nanodiscs or liposome reconstitution for structural studies

• Protein-protein interaction identification:

  • Bacterial two-hybrid screening

  • Co-immunoprecipitation with epitope-tagged uspB

  • Crosslinking followed by mass spectrometry

  • Proximity labeling approaches (BioID, APEX)

  • Split-GFP complementation assays for validation

• Functional validation of interactions:

  • Co-expression studies

  • Mutational analysis of interaction interfaces

  • Competitive inhibition of interactions

  • Phenotypic characterization of interaction-deficient mutants

• Spatial organization in the cell:

  • Super-resolution microscopy to visualize uspB localization

  • Co-localization studies with known membrane proteins

  • Fractionation studies to determine membrane microdomain associations

• Dynamics of interactions:

  • FRET or BRET assays to monitor real-time interactions

  • Single-molecule tracking to analyze diffusion properties and clustering

How does uspB function compare across different pathogenic E. coli strains beyond O7:K1?

To compare uspB function across pathogenic E. coli strains:

• Comparative genomics approach:

  • Analyze uspB sequence conservation across UPEC, EHEC, EPEC, ETEC, and other pathotypes

  • Identify strain-specific variations in uspB sequence or regulatory regions

  • Construct phylogenetic trees of uspB sequences to correlate with pathotype classification

• Functional complementation studies:

  • Express uspB variants from different strains in a common genetic background

  • Test complementation of stress response phenotypes

  • Assess contribution to virulence-associated traits

• Expression pattern analysis:

  • Compare uspB expression levels across strains under identical conditions

  • Determine if regulation differs between pathotypes

  • Correlate expression patterns with virulence potential

• Heterologous strain testing:

  • Generate mutants in multiple strain backgrounds

  • Test for strain-specific phenotypes

  • Identify genetic interactions unique to specific backgrounds

A comparative analysis table can be constructed:

What methodological approaches can elucidate the relationship between uspB and K1 capsule expression in immune evasion?

To investigate the relationship between uspB and K1 capsule in immune evasion:

• Sequential experimental design:

  • Characterize capsule expression in wild-type and uspB mutants using flow cytometry with rEndoNA2-GFP binding

  • Measure polySia production quantitatively using colorimetric or HPLC-based methods

  • Assess transcription of K1-cps locus genes in uspB mutants versus wild-type

• Immune evasion assays:

  • Serum survival assays comparing wild-type, uspB mutant, neuC mutant (K1 capsule-deficient), and double mutants

  • C3b deposition measurements using flow cytometry

  • Phagocytosis assays with human neutrophils and macrophages

  • Complement activation pathway analysis (classical, alternative, lectin)

• Cross-complementation studies:

  • Determine if overexpression of K1 capsule genes can compensate for uspB mutation

  • Test if uspB overexpression affects phenotypes of K1 capsule-deficient strains

• Regulatory interaction mapping:

  • ChIP-seq to identify potential direct regulatory relationships

  • RNA-seq to identify co-regulated gene networks

  • Protein-protein interaction studies between UspB and K1 capsule biosynthesis proteins

• Therapeutic targeting assessment:

  • Test capsule depolymerase (rEndoE) effectiveness on uspB mutants

  • Evaluate synergistic effects of targeting both uspB and K1 capsule simultaneously

What are the optimal conditions for purification and functional analysis of recombinant uspB protein?

For optimal purification and functional analysis of recombinant uspB:

• Expression optimization:

  • Test multiple E. coli expression strains (BL21(DE3), C41(DE3), C43(DE3) for membrane proteins)

  • Optimize induction conditions (temperature, IPTG concentration, duration)

  • Consider inclusion of detergents during expression to improve solubility

• Purification protocol:

  • Cell lysis: Use gentle methods like enzymatic lysis with lysozyme followed by brief sonication

  • Detergent screening: Test multiple detergents (DDM, LDAO, Triton X-100) for optimal extraction

  • Affinity purification: Ni-NTA chromatography with imidazole gradient elution

  • Size exclusion chromatography: Remove aggregates and further purify

• Quality control assessments:

  • SDS-PAGE to verify >90% purity

  • Western blotting to confirm identity

  • Mass spectrometry to verify sequence integrity

  • Dynamic light scattering to assess homogeneity

• Functional reconstitution options:

  • Liposome reconstitution

  • Nanodisc incorporation

  • Amphipol stabilization

• Storage conditions:

  • Store at -20°C/-80°C with aliquoting to avoid freeze-thaw cycles

  • Include 5-50% glycerol as cryoprotectant

  • For working solutions, store at 4°C for up to one week

How can researchers design experiments to overcome functional redundancy among USP family proteins when studying uspB?

To address functional redundancy when studying uspB:

• Systematic mutation approach:

  • Generate single, double, and multiple deletions of usp family genes

  • Create a complete set of uspB+other usp double mutants

  • Construct strains with only uspB remaining (deletion of all other usp genes)

• Phenotypic screening matrix:

  • Test each mutant combination under multiple stress conditions

  • Focus on conditions where single mutants show subtle or no phenotypes

  • Look for synergistic effects in multiple mutants

• Specific vs. overlapping functions:

  • Use transcriptomics to identify genes specifically regulated by uspB

  • Compare protein interaction networks of different USPs

  • Identify conditions where uspB expression patterns differ from other USPs

• Domain-swapping experiments:

  • Create chimeric proteins with domains from different USPs

  • Test complementation of specific phenotypes

  • Identify functional domains unique to uspB

• Controlled expression systems:

  • Use inducible promoters to express uspB at defined levels

  • Compensate for loss of multiple USPs with controlled uspB expression

  • Determine threshold levels needed for function