Recombinant Shigella boydii serotype 18 Undecaprenyl-diphosphatase (uppP)

How does uppP contribute to bacitracin resistance in bacteria?

UppP plays a significant role in bacitracin resistance through competitive binding and increased dephosphorylation of Und-PP. Bacitracin is a mixture of related polycyclic peptides that binds tightly to the pyrophosphate motif of Und-PP in the presence of divalent cations, preventing access to phosphatases and consequently blocking cell wall formation .

Mechanistically:

• Overexpression of uppP results in increased Und-PP phosphatase activity

• This enhances competition with bacitracin for the pyrophosphate motif of Und-PP

• Higher levels of Und-P are maintained even in the presence of bacitracin

Studies have demonstrated that E. coli cells overexpressing uppP could resist up to 200 μg/ml of bacitracin that completely lysed control cells . A 280-fold increase in Und-PP phosphatase activity was observed in membrane extracts of E. coli overexpressing uppP compared to control cells .

What are the optimal conditions for handling and storing Recombinant Shigella boydii serotype 18 Undecaprenyl-diphosphatase?

Based on product information, the following storage and handling guidelines are recommended for Recombinant Shigella boydii serotype 18 Undecaprenyl-diphosphatase :

For experimental work, the protein is typically provided at a quantity of 50 μg, though other quantities may be available. The protein appears to be most stable in a glycerol-containing buffer that prevents protein denaturation during freeze-thaw cycles .

How is the uppP gene conserved across different bacterial species?

Undecaprenyl pyrophosphate phosphatase (uppP) is widely distributed as a single copy in most bacteria, though its essentiality varies across species. Bioinformatic analyses reveal several key characteristics:

• Sequence conservation: The amino acid sequence of uppP shows a large cytoplasmic loop that is conserved in all bacteria .

• Distribution patterns:

  • Present as a single copy in most bacteria

  • Non-essential in E. coli, S. aureus, S. pneumoniae, B. subtilis, and various mycobacteria (M. tuberculosis, M. bovis BCG, M. smegmatis)

• Functional redundancy:

  • In E. coli, deletion of uppP reduces Und-PP phosphatase activity by approximately 75% but does not cause significant growth or morphological defects

  • In Gram-positive bacteria, alternative pathways exist for generating Und-P through undecaprenol kinase activity, which may compensate for uppP deletion

The phylogenetic distribution suggests evolutionary adaptations in how different bacteria process and utilize undecaprenyl phosphate in cell wall biosynthesis.

What methodological approaches can be used to assess the enzymatic activity of uppP in vitro?

To evaluate the enzymatic activity of Recombinant Shigella boydii serotype 18 Undecaprenyl-diphosphatase, several methodological approaches can be employed:

• Radiometric assay using [32P]-labeled substrates

  • Incubate purified uppP with [32P]-labeled Und-PP

  • Measure the release of inorganic phosphate

  • Quantify using thin-layer chromatography or liquid scintillation counting

• Colorimetric phosphate detection

  • Reaction buffer: 50 mM Tris-HCl (pH 7.5), 150 mM NaCl, 10 mM MgCl₂

  • Substrate: Und-PP (typically 50-100 μM)

  • Incubate at 30-37°C for 30 minutes

  • Detect released phosphate using malachite green or similar colorimetric reagents

• Competitive binding assay with bacitracin

  • Measure enzyme activity in the presence of increasing concentrations of bacitracin

  • Calculate IC₅₀ values to determine binding affinity

  • Use fluorescently labeled bacitracin derivatives for direct binding studies

• Mass spectrometry-based approach

  • Incubate purified enzyme with synthetic Und-PP substrate

  • Extract lipids using chloroform/methanol mixture

  • Analyze product formation by HPLC-MS/MS

  • Quantify conversion of Und-PP to Und-P

When designing activity assays, it's important to consider the membrane-associated nature of uppP and the hydrophobicity of its substrates. Detergents like Triton X-100 or DDM at concentrations just above their critical micelle concentration may be necessary to solubilize the substrate and maintain enzyme activity.

How does the undecaprenyl phosphate cycle differ between Gram-positive and Gram-negative bacteria, specifically regarding uppP function?

The undecaprenyl phosphate cycle shows significant differences between Gram-positive and Gram-negative bacteria, particularly regarding alternative pathways and enzyme contributions:

Gram-negative bacteria (e.g., E. coli, S. boydii):

• De novo synthesis: The primary pathway involves dephosphorylation of Und-PP by uppP, which accounts for approximately 75% of the total Und-PP phosphatase activity .

• Recycling pathway: Additional phosphatases (YbjG, PgpB) function primarily in the recycling of Und-PP generated during cell wall synthesis .

• Absence of undecaprenol (Und-OH): Und-OH is typically not detectable in membrane extracts of E. coli, suggesting limited contribution from kinase-mediated phosphorylation of Und-OH .

What experimental approaches can be used to elucidate the structure-function relationships of uppP?

Understanding the structure-function relationships of uppP requires a multi-faceted approach combining molecular, biochemical, and structural techniques:

Site-directed mutagenesis

Target conserved residues, particularly in the cytoplasmic loop and putative active site:

• Arginine residues involved in phosphate binding

• Conserved aspartate/glutamate residues for catalysis

• Transmembrane regions for substrate binding

Analyze mutants for:

• Changes in enzyme activity using phosphatase assays

• Alterations in bacitracin resistance

• Effects on protein localization and membrane topology

Truncation and domain analysis

• Generate truncated variants to identify minimal catalytic domains

• Create chimeric proteins with homologous phosphatases to map functional regions

• Express soluble domains for crystallization attempts

Topology mapping

• PhoA::LacZ reporter fusions to determine membrane orientation

• Cysteine accessibility methods using maleimide-polyethylene glycol probes to interrogate native conformation in situ

• Fluorescence resonance energy transfer (FRET) to analyze conformational changes

Structural analysis

• Cryo-electron microscopy for membrane protein structure

• X-ray crystallography of solubilized protein or soluble domains

• NMR for dynamic structural information of specific domains

Interaction studies

• Pull-down assays to identify protein-protein interactions

• Crosslinking studies to capture transient interactions

• Surface plasmon resonance (SPR) to measure binding kinetics with substrates and inhibitors

Example experimental workflow:

• Generate a panel of point mutations in conserved residues

• Express and purify mutant proteins

• Perform in vitro phosphatase assays to determine kinetic parameters (Km, Vmax)

• Test bacitracin resistance in vivo with complementation studies

• Analyze protein folding and stability using circular dichroism

• Determine membrane topology using reporter fusions

These approaches would provide comprehensive insights into the structural elements critical for uppP function and may identify potential targets for antimicrobial development.

How can recombinant uppP be effectively expressed and purified for biochemical studies?

Effective expression and purification of Recombinant Shigella boydii serotype 18 Undecaprenyl-diphosphatase requires careful consideration of its membrane-associated nature. Here is a comprehensive protocol:

Expression Protocol:

• Construct preparation:

  • Clone the uppP gene (1116 bp) into an expression vector with an inducible promoter (T7, araBAD)

  • Include a C-terminal His6-tag or alternative affinity tag (Strep-tag II often works well for membrane proteins)

  • Consider using a fusion partner (MBP, SUMO) to enhance solubility

  • Include a TEV or PreScission protease cleavage site for tag removal

• Host strain selection:

  • E. coli C41(DE3) or C43(DE3) - specialized for membrane protein expression

  • Alternatively, BL21(DE3) with pLysS to control basal expression

  • Consider Lemo21(DE3) for tunable expression level

• Culture conditions:

  • Use rich media (TB or 2xYT) for high cell density

  • Grow at 37°C to OD600 of 0.6-0.8

  • Induce with low concentrations of inducer (0.1-0.5 mM IPTG)

  • Shift to lower temperature (16-20°C) post-induction

  • Continue expression for 16-20 hours

Purification Protocol:

• Cell lysis:

  • Harvest cells by centrifugation (6,000 x g, 15 min, 4°C)

  • Resuspend in buffer containing 50 mM Tris-HCl pH 8.0, 300 mM NaCl, 10% glycerol, 1 mM PMSF, protease inhibitor cocktail

  • Lyse using French press (15,000 psi) or sonication

• Membrane fraction isolation:

  • Remove cell debris by centrifugation (15,000 x g, 30 min, 4°C)

  • Ultracentrifuge supernatant (100,000 x g, 1 hour, 4°C)

  • Collect membrane pellet

• Protein solubilization:

  • Resuspend membrane pellet in solubilization buffer: 50 mM Tris-HCl pH 8.0, 300 mM NaCl, 10% glycerol, 1% detergent

  • Test multiple detergents (DDM, LDAO, LMNG) at 1% w/v

  • Incubate with gentle agitation for 2 hours at 4°C

  • Remove insoluble material by ultracentrifugation (100,000 x g, 30 min, 4°C)

• Affinity chromatography:

  • Load solubilized membrane fraction onto Ni-NTA or TALON resin

  • Wash with 10-20 column volumes of wash buffer: 50 mM Tris-HCl pH 8.0, 300 mM NaCl, 10% glycerol, 0.05% detergent, 20 mM imidazole

  • Elute with 250-300 mM imidazole

• Secondary purification:

  • Perform size exclusion chromatography (Superdex 200) in buffer containing 50 mM Tris-HCl pH 8.0, 150 mM NaCl, 10% glycerol, 0.05% detergent

  • Optional: Ion exchange chromatography for additional purity

• Quality control:

  • Assess purity by SDS-PAGE (>90% purity)

  • Verify activity using phosphatase assays

  • Determine oligomeric state by SEC-MALS

Storage:

Store purified protein in 50 mM Tris-HCl pH 8.0, 150 mM NaCl, 50% glycerol, 0.02% detergent at -20°C for short term or flash-freeze in liquid nitrogen and store at -80°C for long term .

What is known about the potential of uppP as a target for antimicrobial development?

Undecaprenyl-diphosphatase (uppP) represents a promising target for antimicrobial development due to its critical role in bacterial cell wall biosynthesis. Several factors make it particularly attractive:

Key advantages as a drug target:

• Essential pathway involvement: UppP participates in the undecaprenyl phosphate cycle, which is critical for peptidoglycan, capsular polysaccharide, and O-antigen biosynthesis .

• Virulence association: UppP has been implicated in virulence and antibiotic resistance in several pathogenic bacteria including Mycobacterium tuberculosis .

• Absence in eukaryotes: The lack of homologous pathways in humans reduces the likelihood of off-target effects.

• Accessible location: As an integral membrane protein with a large cytoplasmic domain, uppP presents potentially druggable binding sites .

Current research approaches:

• Structure-based drug design:

  • Targeting the active site or the conserved cytosolic loop of uppP

  • In silico screening using homology models

  • Fragment-based approaches to identify lead compounds

• Natural product screening:

  • Bacitracin serves as a prototype for indirect targeting by sequestering the substrate

  • Screening natural product libraries for direct uppP inhibitors

• High-throughput screening strategies:

  • Phosphatase activity assays adapted to plate format

  • Growth inhibition assays with targeted libraries

  • Whole-cell screens with chemical genetic approaches

• Synergistic approaches:

  • Combining uppP inhibitors with existing cell wall-targeting antibiotics

  • Dual targeting of multiple steps in the undecaprenyl phosphate cycle

Challenges and considerations:

• Functional redundancy: The presence of alternative phosphatases (YbjG, PgpB) in some bacteria may require dual targeting approaches .

• Species-specific differences: Variations in the essentiality of uppP between Gram-positive and Gram-negative bacteria necessitate careful target validation .

• Membrane protein targeting: The membrane-embedded nature of uppP presents challenges for inhibitor delivery and binding.

• Resistance mechanisms: Potential upregulation of alternative phosphatases or mutations that affect inhibitor binding must be considered.

The unique position of uppP at the interface of lipid and carbohydrate metabolism in bacterial cell wall synthesis makes it a promising but challenging target for next-generation antimicrobials, particularly against multi-drug resistant Shigella and other enteric pathogens.

How can researchers investigate the role of uppP in Shigella pathogenesis using genetic manipulation techniques?

Investigating the role of uppP in Shigella pathogenesis requires sophisticated genetic manipulation techniques adapted for this organism. Here is a comprehensive methodological approach:

Gene knockout and complementation

Allelic exchange protocol:

• Create a suicide vector containing homologous regions flanking uppP with an antibiotic resistance cassette

• Transform S. boydii by electroporation or conjugation

• Select for integrants on appropriate antibiotics

• Counter-select with sucrose (if using sacB) for double recombinants

• Verify deletion by PCR and sequencing

Complementation strategy:

• Clone wild-type uppP into a low-copy Shigella-compatible plasmid (pWSK29 or pACYC184)

• Include native promoter or inducible promoter (arabinose, tetracycline)

• Transform into the ΔuppP strain

• Perform functional assays to confirm complementation

Conditional expression systems

For essential genes or to study depletion phenotypes:

• Replace native promoter with an inducible promoter (tetracycline or arabinose)

• Alternative approach: Create a temperature-sensitive allele

• Design degron-tagged versions for rapid protein depletion

Point mutations and domain analysis

• Use site-directed mutagenesis to create specific point mutations

• Target conserved residues in the cytoplasmic loop

• Create chimeric proteins with other phosphatases

• Express truncated versions to identify functional domains

Reporter fusion constructs

• Create transcriptional fusions (uppP promoter-lacZ) to study regulation

• Generate translational fusions (uppP-GFP) to analyze localization

• Design bacterial two-hybrid constructs to identify protein interactions

Virulence and phenotypic assays

Cell culture models:

• Invasion assays using HeLa or Caco-2 cells

• Plaque formation in cell monolayers

• Intracellular growth assays

In vivo models:

• Sereny test (guinea pig keratoconjunctivitis)

• Mouse pulmonary infection model

• Infant rabbit model of shigellosis

Cell wall integrity assays:

• Susceptibility to cell wall-targeting antibiotics (bacitracin, vancomycin)

• Measuring release of peptidoglycan fragments

• Electron microscopy to analyze cell morphology

• Congo red binding to assess virulence plasmid maintenance

Growth characteristics:

• Growth curves in standard and stress conditions

• Survival in acidic environments

• Resistance to oxidative stress

Strain selection considerations

When performing genetic manipulations with Shigella boydii:

• Use sequenced strains to facilitate genetic engineering (e.g., serotype 2a strains SF301, 2457, or serotype 5a strain M90)

• Grow at temperatures below 35°C to maintain the virulence plasmid

• Use Congo red agar to monitor virulence plasmid retention (CR+ colonies are virulent)

• Consider using rich defined medium (EZ-RDM) for reproducible gene expression studies

This methodological framework provides a comprehensive approach to investigating the role of uppP in Shigella pathogenesis, from basic genetic manipulation to sophisticated virulence assays.