Recombinant Bordetella avium Undecaprenyl-diphosphatase (uppP)

What is the biological function of Bordetella avium Undecaprenyl-diphosphatase (uppP) in bacterial cell wall synthesis?

Undecaprenyl-diphosphatase (uppP, formerly known as bacA) is an integral membrane protein that plays a critical role in bacterial cell wall synthesis. It catalyzes the dephosphorylation of undecaprenyl pyrophosphate (C55-PP) to undecaprenyl phosphate (C55-P), which serves as an essential carrier lipid in the bacterial cell wall synthesis pathway .

In the bacterial cell wall synthesis process:

• C55-PP is synthesized by undecaprenyl pyrophosphate synthase (UppS) through consecutive condensation reactions of eight molecules of isopentenyl pyrophosphate with farnesyl pyrophosphate

• UppP then dephosphorylates C55-PP to C55-P

• C55-P serves as a carrier lipid for peptidoglycan precursors, enabling their transport across the cytoplasmic membrane

This process occurs in two distinct pathways:

• De novo synthesis pathway

• Recycling pathway

The significance of uppP is highlighted by the fact that in Escherichia coli, while multiple enzymes (uppP, pgpB, ybjG, and lpxT) exhibit C55-PP phosphatase activity, uppP generates approximately 75% of the total cellular C55-PP phosphatase activity .

What experimental approaches can be used to investigate the catalytic mechanism of B. avium uppP?

Several experimental approaches can be employed to elucidate the catalytic mechanism of B. avium uppP:

Site-directed mutagenesis studies

Based on research with E. coli UppP, creating mutations in the conserved motifs can identify critical residues:

• Mutate residues in the (E/Q)XXXE motif (e.g., E17A, E21A, and double mutation E17A/E21A)

• Mutate residues in the PGXSRSXXT motif (e.g., S173A, R174A, T178A)

• Mutate the conserved histidine residue (e.g., H30A)

The impact of these mutations on enzyme kinetics can be assessed using the following parameters:

Table based on E. coli UppP data

Structural modeling and molecular dynamics

• Utilize Rosetta membrane ab initio modeling to construct three-dimensional models

• Validate models through molecular dynamics simulation

• Analyze substrate binding pocket interactions

• Identify potential H-bond formations between key residues and substrate moieties

Enzyme kinetics assays

A standard assay for measuring uppP activity:

• Reaction mixture: 50 mM Hepes (pH 7.0), 150 mM NaCl, 10 mM MgCl₂, 0.02% DDM, varying concentrations of Fpp (0.3-57 μM), and 20-40 nM purified uppP

• Incubate at 37°C

• Quench by adding Malachite Green reagent

• Measure released phosphate at 650 nm

• Quantify based on phosphate standard curve

How can recombinant B. avium uppP be optimally expressed and purified for functional studies?

Based on established protocols for membrane proteins and related recombinant proteins:

Expression system:

• Host organism: E. coli C41(DE3) strain, optimized for membrane protein expression

• Vector: pET system with appropriate tag (His-tag is commonly used)

• Induction conditions: 0.5 mM ISOPROPYL β-D-THIOGALACTOSIDE at OD₆₀₀ of approximately 0.9

• Growth temperature: 37°C for 5 hours post-induction

Purification protocol:

• Cell lysis:

  • Resuspend cells in buffer A (50 mM Tris, pH 7.5, 500 mM NaCl)

  • Disrupt cells using a cell disruption system

  • Collect membrane fraction by ultracentrifugation at 40,000 rpm for 1.5 hours

• Solubilization:

  • Solubilize membrane pellet in buffer A with 1% (w/v) n-dodecyl-β-D-maltopyranoside (DDM)

• Affinity purification:

  • For His-tagged constructs, use nickel affinity chromatography

  • Elute with imidazole gradient

• Storage:

  • Store in Tris-based buffer with 50% glycerol at -20°C

  • For extended storage, conserve at -80°C

  • Avoid repeated freeze-thaw cycles

  • Working aliquots can be stored at 4°C for up to one week

• Quality control:

  • Verify purity using SDS-PAGE (>90% purity is desirable)

  • Confirm identity by Western blot with anti-His antibodies

  • Assess activity using the phosphate release assay described above

What role does uppP play in bacterial antibiotic resistance?

UppP (previously known as bacA) is implicated in bacterial antibiotic resistance through several mechanisms:

• Bacitracin resistance:

  • Bacitracin is an antibiotic that binds to undecaprenyl pyrophosphate (C55-PP), preventing its dephosphorylation

  • UppP overexpression can confer resistance to bacitracin by maintaining sufficient levels of undecaprenyl phosphate (C55-P) for cell wall synthesis despite bacitracin presence

  • This is why uppP is sometimes referred to as "Bacitracin resistance protein"

• Cell wall integrity:

  • By ensuring proper cell wall synthesis through maintenance of the C55-P carrier lipid pool, uppP contributes to cell wall integrity

  • A robust cell wall provides intrinsic resistance against various antibiotics targeting cell wall synthesis

• Essential for survival:

  • While individual phosphatases (uppP, pgpB, ybjG) can be disrupted without lethality in E. coli, simultaneous inactivation of uppP, ybjG, and pgpB causes cell lysis due to depletion of C55-P and accumulation of peptidoglycan nucleotide precursors

  • This essentiality makes uppP a potential antibiotic target itself

Research has shown that uppP's role in antibiotic resistance makes it a target for developing new antimicrobial agents, particularly against gram-negative pathogens like Bordetella species.

Sequence homology and conserved domains:

From the available sequences of uppP proteins from different bacterial species:

All these proteins share the fundamental enzymatic function of dephosphorylating undecaprenyl pyrophosphate to undecaprenyl phosphate, but may exhibit species-specific differences in:

• Substrate specificity

• Reaction kinetics

• Regulatory mechanisms

• Membrane topology

Potential functional differences:

• Some bacterial species have multiple enzymes with C55-PP phosphatase activity (e.g., E. coli has uppP, pgpB, ybjG, and lpxT)

• The contribution of uppP to total C55-PP phosphatase activity may vary between species

• Localization and topology differences may influence substrate accessibility and regulation

A comprehensive comparative biochemical analysis would require experimental characterization of each protein under identical conditions.

What immunogenic potential does B. avium uppP have and how might it be utilized in vaccine development?

While the provided search results don't directly address the immunogenic potential of B. avium uppP specifically, we can draw insights from studies on other Bordetella proteins:

Potential as a vaccine antigen:

Several factors suggest uppP could have potential as a vaccine antigen:

• Membrane localization: As an integral membrane protein, portions of uppP are likely exposed on the bacterial surface, making it accessible to immune recognition

• Essentiality: Its crucial role in cell wall synthesis makes it a conserved target less likely to undergo antigenic variation

• Precedent with other proteins: Studies on other Bordetella proteins show that recombinant proteins can induce protective immune responses. For example:

  • Recombinant outer membrane porin protein (PPP) from B. bronchiseptica provided 62.5% protection

  • Recombinant lipoprotein (PL) provided 50% protection against challenges

Experimental approach for evaluating vaccine potential:

Based on methodologies used for other Bordetella proteins, a research approach could include:

• Recombinant protein production:

  • Express and purify B. avium uppP with appropriate tags

  • Verify protein integrity and activity

• Immunization studies:

  • Vaccinate animal models (e.g., mice) with recombinant uppP (typical dose: 50 μg/dose)

  • Include appropriate adjuvants (e.g., Freund's complete adjuvant)

  • Administer multiple doses (e.g., two doses at 2-week intervals)

• Immune response evaluation:

  • Measure antibody titers using ELISA

  • Determine IgG subtypes (IgG1, IgG2a) to assess immune response type

  • Analyze cytokine profiles to determine Th1/Th2 balance

• Challenge studies:

  • Challenge vaccinated animals with virulent B. avium

  • Monitor survival rates and bacterial loads

  • Compare with control groups to determine protection ratio

A successful vaccine candidate would induce both humoral (antibody-mediated) and cell-mediated immune responses, with a preference for balanced Th1/Th2 responses.

How can transposon mutagenesis be used to study the function of uppP in B. avium?

Transposon mutagenesis is a powerful tool for studying gene function in bacteria. Based on methodologies described in the search results, here's an approach for studying B. avium uppP:

Transposon mutagenesis protocol:

• Transposon selection:

  • Utilize a transposon like TnphoA that creates gene fusions with alkaline phosphatase, allowing detection of membrane protein orientation

  • This approach has been successfully used in B. avium for other genes

• Conjugation and mutant library generation:

  • Create a donor strain containing the transposon (e.g., SM10(pCOS5::TnphoA))

  • Use a recipient B. avium strain with appropriate antibiotic resistance (e.g., rifampin resistance)

  • Perform matings on BHI agar by mixing equal aliquots of log-phase cultures

  • Incubate overnight at 30°C

  • Select transconjugants on media with appropriate antibiotics (rifampin, streptomycin, kanamycin)

  • Verify loss of helper plasmid by screening for chloramphenicol sensitivity

• Screening for uppP mutants:

  • Use PCR with transposon-specific and uppP-specific primers

  • Alternatively, employ BCIP (bromo-chloro-indolyl phosphate) screening if using TnphoA

  • Modified BCIP assay conditions: 150 mM Tris buffer (pH 8.0) with 430 μM BCIP, allowing for long-term cell survival during screening

Functional characterization of uppP mutants:

• Growth phenotype analysis:

  • Compare growth rates in various media

  • Test sensitivity to antibiotics targeting cell wall synthesis, particularly bacitracin

  • Examine morphological changes using microscopy

• Cell wall synthesis assessment:

  • Analyze peptidoglycan composition

  • Measure accumulation of cell wall precursors

• Complementation studies:

  • Introduce wild-type uppP gene on a plasmid

  • Verify restoration of normal phenotype

• Gene expression analysis:

  • Study effects of iron limitation on uppP expression, as iron regulation affects multiple B. avium outer membrane proteins

  • Use quantitative assays with NPP (p-nitrophenyl phosphate) to measure gene expression levels if using TnphoA fusions

This approach would provide insights into the essentiality of uppP in B. avium, its regulation, and its role in antibiotic resistance and cell wall synthesis.

What role does the BvgAS system play in regulating uppP expression in Bordetella species?

The BvgAS two-component regulatory system is a master regulator of virulence in Bordetella species. While the search results don't directly address BvgAS regulation of uppP, we can infer potential relationships based on Bordetella biology:

The BvgAS system in Bordetella:

• Function and modulation:

  • BvgAS responds to environmental signals like temperature and chemical components (nicotinic acids, magnesium sulfate)

  • It controls switching between virulence-activated (Bvg+) and virulence-repressed (Bvg-) states

  • In the Bvg+ phase, BvgS phosphorylates BvgA, which binds to promoter regions of Bvg-activated genes and initiates transcription

• Scope of regulation:

  • The BvgAS regulon induces expression of more than 550 genes in B. pertussis

  • It controls expression of major virulence factors including filamentous hemagglutinin, adenylate cyclase toxin, pertussis toxin, and fimbriae

Potential regulation of uppP by BvgAS:

• Cell wall synthesis and virulence:

  • As uppP is essential for cell wall synthesis, its expression might be coordinated with virulence factor expression

  • The integrity of the cell envelope is critical during infection, suggesting potential co-regulation with virulence factors

• Bvg phases and bacterial persistence:

  • The Bvg- phase has been implicated in bacterial persistence and environmental survival

  • uppP's role in maintaining cell wall integrity could make it important in both phases:

    • Bvg+ phase: Supporting active growth during infection

    • Bvg- phase: Maintaining cell wall integrity during persistence

• Experimental approach to investigate BvgAS regulation of uppP:

  • Compare uppP expression in wild-type, Bvg+ phase-locked, and Bvg- phase-locked mutants

  • Analyze uppP promoter for potential BvgA binding sites

  • Perform chromatin immunoprecipitation (ChIP) to detect BvgA binding to the uppP promoter

  • Use reporter gene fusions to measure uppP expression under different Bvg-modulating conditions

The conservation of bvgA and bvgS homologs throughout Bordetella species, including animal-associated and environmental species , suggests that this regulatory system might influence uppP expression in B. avium as well.

How does the lipid environment affect the enzymatic activity of recombinant uppP?

The lipid environment significantly impacts the activity of membrane proteins like uppP. Although the search results don't specifically address B. avium uppP in this context, evidence from related proteins provides insights:

Lipid dependencies of translocases and phosphatases:

• Detergent sensitivity:

  • MraY translocases (another enzyme family involved in bacterial cell wall synthesis) from Gram-negative bacteria show sensitivity to detergents

  • These enzymes require nanodiscs containing negatively charged lipids for optimal activity

  • As uppP is also an integral membrane protein from Gram-negative bacteria, it likely exhibits similar dependencies

• Reconstitution requirements:

  • For functional studies, uppP would ideally be reconstituted in a lipid environment mimicking its native membrane

  • Nanodiscs or liposomes containing a mixture of phospholipids found in bacterial membranes may preserve activity better than detergent micelles

Methodological approaches to study lipid effects:

• Protein reconstitution systems:

  • Nanodiscs: Disc-shaped phospholipid bilayers stabilized by membrane scaffold proteins

  • Liposomes: Spherical vesicles composed of phospholipids

  • Bicelles: Disc-shaped lipid assemblies composed of long-chain and short-chain phospholipids

• Lipid composition variables to test:

  • Phospholipid head group charge (negative, neutral, positive)

  • Acyl chain length and saturation

  • Presence of specific bacterial lipids (e.g., cardiolipin)

  • Membrane fluidity and thickness

• Activity assay in different lipid environments:

  • Standard assay: 50 mM Hepes (pH 7.0), 150 mM NaCl, 10 mM MgCl₂

  • Substitute detergent (DDM) with various lipid reconstitution systems

  • Measure activity using Malachite Green phosphate detection

  • Compare kinetic parameters (Km, kcat) across different lipid compositions

This kind of analysis would provide valuable insights into the optimal conditions for studying recombinant B. avium uppP and might reveal important aspects of its in vivo regulation and function.