Recombinant Yersinia pestis bv. Antiqua Probable ubiquinone biosynthesis protein UbiB (ubiB)

What is the role of UbiB in Yersinia pestis and how does it contribute to pathogenicity?

UbiB functions as a probable protein kinase involved in ubiquinone (UQ) biosynthesis in Yersinia pestis. Ubiquinone, also known as coenzyme Q, plays a critical role in bacterial bioenergetics as an electron carrier in aerobic respiration. The UbiB protein exhibits ATPase activity and is essential for the oxygen-dependent hydroxylation reactions in the UQ biosynthetic pathway.

Research has shown that UbiB belongs to a multiprotein UQ biosynthesis complex, where it works alongside other accessory factors such as UbiJ and UbiK. The UbiJ protein contains an SCP2 domain (sterol carrier protein 2) that binds hydrophobic UQ biosynthetic intermediates . While not directly established as a virulence factor, UbiB's role in energy metabolism may indirectly impact Y. pestis survival under varying environmental conditions, particularly during host infection where oxygen availability fluctuates significantly.

Studies investigating oxygen-independent UQ biosynthesis have demonstrated that deletion of ubiB significantly diminishes UQ8 biosynthesis under aerobic conditions, indicating its crucial role in the canonical O2-dependent pathway . These findings suggest that targeting UbiB could potentially disrupt energy metabolism in Y. pestis, presenting a novel approach to antimicrobial development.

How does the oxygen-dependent ubiquinone biosynthesis pathway involving UbiB differ from the oxygen-independent pathway in Yersinia pestis?

Yersinia pestis possesses two distinct pathways for ubiquinone (UQ) biosynthesis: an oxygen-dependent pathway (requiring UbiB) and an oxygen-independent pathway (utilizing different proteins). These pathways represent a sophisticated metabolic adaptation that allows the bacterium to synthesize UQ across varying oxygen conditions.

Oxygen-Dependent Pathway (UbiB-dependent):

• Requires molecular oxygen as a co-substrate for hydroxylation reactions

• UbiB functions as an accessory factor with ATPase activity

• Involves hydroxylases UbiI, UbiH, and UbiF that use O2 directly

• Deletion of ubiB results in minimal UQ production under aerobic conditions

• UbiJ and UbiK serve as additional accessory factors in this pathway

Oxygen-Independent Pathway:

• Functions without requiring molecular oxygen

• Relies on UbiT (YhbT), UbiU (YhbU), and UbiV (YhbV) proteins

• UbiU and UbiV form a heterodimer, with each binding a 4Fe-4S cluster

• These proteins represent a novel class of O2-independent hydroxylases

• Essential for UQ biosynthesis under anaerobic conditions

Comparative studies have shown that certain enzymes like UbiA, UbiE, and UbiG are common to both pathways, while others are pathway-specific. When ubiB is deleted, Y. pestis can still produce limited amounts of UQ8 under aerobic conditions but significantly less than wild-type strains . This dual pathway system enables Y. pestis to maintain energy production across the entire O2 range, which is crucial for its ability to colonize environments with large O2 gradients or fluctuating O2 levels—a key adaptation for its pathogenic lifestyle.

What are the optimal conditions for expression and purification of recombinant UbiB from Y. pestis bv. Antiqua?

Based on established protocols for recombinant UbiB expression, the following optimized conditions have been determined:

Expression System:

• Host: E. coli expression system

• Vector: pET-based vectors with T7 promoter

• Fusion tag: N-terminal His-tag for purification via affinity chromatography

• Expression temperature: 25-30°C (reduced temperature minimizes inclusion body formation)

• Induction: 0.5-1.0 mM IPTG for 4-6 hours

Purification Protocol:

• Cell lysis in Tris/PBS-based buffer (pH 8.0) containing 6% Trehalose

• Affinity chromatography using Ni-NTA resin

• Optional: Size exclusion chromatography to remove aggregates

• Storage as lyophilized powder or in buffer with 50% glycerol at -20°C/-80°C

Quality Control Parameters:

• Purity assessment: >90% as determined by SDS-PAGE

• Activity verification: ATPase assay

• Storage recommendations: Avoid repeated freeze-thaw cycles; store working aliquots at 4°C for up to one week

Reconstitution Guidelines:

• Briefly centrifuge the vial prior to opening

• Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL

• Add glycerol to 5-50% final concentration for long-term storage

• Aliquot for storage at -20°C/-80°C

These conditions have been shown to yield functionally active UbiB protein suitable for biochemical and structural studies while minimizing protein aggregation and maintaining stability.

What methodologies can be used to assess the functional activity of recombinant UbiB in vitro?

Assessing the functional activity of recombinant UbiB requires multiple complementary approaches:

1. ATPase Activity Assay:

• Measure ATP hydrolysis using colorimetric malachite green assay

• Monitor release of inorganic phosphate

• Typical reaction conditions: 50 mM Tris-HCl (pH 7.5), 5 mM MgCl2, 1 mM ATP

• ATPase activity can be quantified as μmol Pi released/min/mg protein

2. Ubiquinone Biosynthesis Reconstitution:

• In vitro reconstitution with other purified Ubi proteins

• Monitor conversion of 4-hydroxybenzoic acid to ubiquinone intermediates

• Analysis by HPLC-MS to detect UQ biosynthetic intermediates

• Compare reactions with and without UbiB to confirm its role

3. Protein-Protein Interaction Studies:

• Pull-down assays using His-tagged UbiB

• Crosslinking experiments to capture transient interactions

• Surface plasmon resonance (SPR) to measure binding kinetics with other Ubi proteins

4. Complementation Studies:

• Transform ubiB-deficient E. coli or Y. pestis with recombinant UbiB

• Measure restoration of ubiquinone levels by HPLC-MS

• Assess growth recovery under aerobic conditions

5. Iron-Sulfur Cluster Analysis:

• UV-visible spectroscopy to detect characteristic absorption peaks

• Electron paramagnetic resonance (EPR) spectroscopy

• Quantification of iron and sulfur content

These methodologies provide a comprehensive assessment of UbiB functionality, from its enzymatic activity to its role in the broader context of ubiquinone biosynthesis. Successful activity verification is essential before using recombinant UbiB in more complex experimental systems.

How does UbiB interact with other components of the ubiquinone biosynthesis pathway in Y. pestis?

UbiB participates in a complex network of interactions with other ubiquinone biosynthesis proteins in Y. pestis. These interactions are critical for coordinating the multistep process of UQ synthesis:

Key Protein-Protein Interactions:

• UbiB interacts with UbiJ and UbiK as part of a multiprotein UQ biosynthesis complex

• The SCP2 domain of UbiJ binds hydrophobic UQ biosynthetic intermediates, suggesting UbiB may work in concert with UbiJ to facilitate these reactions

• UbiB likely associates with the hydroxylases (UbiI, UbiH, UbiF) involved in the oxygen-dependent pathway

Functional Cooperation:

• UbiB provides energy through ATP hydrolysis to drive energetically unfavorable reactions

• It may help position substrates correctly for modification by other enzymes

• Studies suggest UbiB plays a role in the activation or regulation of other Ubi proteins

Pathway Integration:

• In the aerobic pathway, UbiB is essential for the activity of oxygen-dependent hydroxylases

• When oxygen is limited, the UbiU-UbiV system (part of the O2-independent pathway) can compensate for UbiB's function

• Crossover between pathways occurs at specific points, with UbiA, UbiE, and UbiG functioning in both pathways

Regulatory Relationships:

• Expression patterns suggest coordinated regulation of UbiB with other UQ biosynthesis genes

• The deletion of ubiB affects the expression of other UQ biosynthesis genes, indicating potential regulatory feedback mechanisms

Understanding these interactions is crucial for developing strategies to disrupt UQ biosynthesis as a potential antimicrobial approach against Y. pestis.

What are the challenges in expressing and maintaining stability of recombinant UbiB for structural studies?

Structural studies of recombinant UbiB from Y. pestis present several significant challenges:

Expression Challenges:

• Membrane association makes UbiB difficult to express in soluble form

• High-level expression often leads to inclusion body formation

• E. coli expression systems may produce improperly folded protein

• Codon usage differences between Y. pestis and expression hosts can limit yields

Stability Concerns:

• UbiB tends to aggregate during concentration procedures

• Multiple freeze-thaw cycles significantly reduce activity

• The protein shows limited stability at room temperature

• Storage in buffer without glycerol or trehalose results in rapid activity loss

Purification Difficulties:

• Detergents required for extraction may interfere with structural studies

• Affinity tags can influence protein folding and crystal packing

• Heterogeneous post-translational modifications complicate structural analysis

• Removal of affinity tags often results in precipitation

Strategies to Overcome These Challenges:

• Expression optimization:

  • Use low temperature (16-25°C) and reduced inducer concentration

  • Co-express with chaperones to improve folding

  • Consider cell-free expression systems

• Stability enhancement:

  • Add stabilizing agents such as trehalose (6%) to buffers

  • Store with glycerol (50% final concentration)

  • Develop nanobodies or other binding partners to stabilize conformation

• Construct design:

  • Create truncated versions removing flexible regions

  • Design fusion proteins with well-folded partners (MBP, SUMO)

  • Introduce surface mutations to reduce aggregation

• Alternative approaches:

  • Consider lipid nanodiscs for membrane-associated regions

  • Use cryo-EM instead of crystallography

  • Employ hydrogen-deuterium exchange mass spectrometry for structural insights

These challenges highlight why high-resolution structures of UbiB proteins remain limited despite their importance in bacterial metabolism.

How can recombinant UbiB be used to screen for potential inhibitors as antimicrobial agents against Y. pestis?

Recombinant UbiB offers a valuable platform for screening potential inhibitors as antimicrobial agents against Y. pestis through the following approaches:

1. High-Throughput Screening Assays:

• ATPase activity-based screening

  • Measure inhibition of ATP hydrolysis using colorimetric or luminescence-based assays

  • Primary screen of compound libraries at single concentration (10-50 μM)

  • Secondary dose-response curves for hit validation (IC50 determination)

• Thermal shift assays

  • Monitor protein thermal stability changes upon inhibitor binding

  • Quantify shifts in melting temperature (Tm) as indicators of binding

2. Structure-Based Virtual Screening:

• In silico docking against UbiB homology models

• Fragment-based approaches to identify binding hotspots

• Molecular dynamics simulations to assess inhibitor stability

3. Validation in Cellular Systems:

• Growth inhibition assays in Y. pestis and E. coli expressing recombinant UbiB

• Measurement of UQ levels following inhibitor treatment using HPLC-MS

• Comparison between wild-type and ubiB-deficient strains to confirm target specificity

4. Combined Screening Approach:

• Initial screening against purified UbiB

• Secondary assays using bacterial membrane fractions

• Tertiary validation in whole cells under varying oxygen conditions

5. Resistance Development Studies:

• Long-term passage experiments with sub-inhibitory concentrations

• Sequencing of resistant mutants to identify resistance mechanisms

• Structure-activity relationship studies to overcome resistance

This systematic approach provides a pipeline for discovering novel UbiB inhibitors with potential development into antimicrobials against Y. pestis. The identification of compounds that selectively target the UbiB-dependent aerobic pathway could lead to oxygen-dependent antimicrobials, representing a novel therapeutic strategy against plague .

What is the relationship between UbiB function and the virulence of Y. pestis in different infection models?

The relationship between UbiB function and Y. pestis virulence is complex and dependent on the infection model and route of administration:

In Bubonic Plague Models:

• UbiB's role in ubiquinone biosynthesis becomes critical when Y. pestis encounters iron-limited environments

• Studies with Y. pestis mutants in related metabolic pathways show that iron acquisition systems are particularly important in bubonic plague models

• The oxygen-dependent pathway involving UbiB may be crucial during initial infection stages when bacteria are in subcutaneous tissues where oxygen is present

In Pneumonic Plague Models:

• Respiratory infections present varying oxygen gradients where both oxygen-dependent (UbiB) and oxygen-independent pathways may be important

• The ability to synthesize ubiquinone across oxygen gradients likely contributes to Y. pestis success in lung tissues

In Septicemic Plague Models:

• When bacteria are directly in the bloodstream, alternative iron acquisition systems may be more effective than those linked to UbiB-dependent metabolism

• Studies show that the survival rates of wild-type and metabolic mutants are similar in blood or serum, suggesting UbiB may be less critical in septicemic models

Host-Pathogen Interactions:

• UbiB's role in energy metabolism affects the bacterium's ability to resist host defenses

• Macrophage survival assays indicate that metabolic adaptability is crucial for intracellular persistence

• The ability to switch between ubiquinone biosynthesis pathways may help Y. pestis evade host immune responses that create oxygen-restricted environments

Experimental Evidence:

• Transcriptomic studies reveal that expression of metabolic genes, including those related to ubiquinone biosynthesis, is differentially regulated during infection

• Mutants in related metabolic pathways show attenuated virulence that can be partially restored through iron supplementation

Understanding this relationship provides insight into how Y. pestis adapts its metabolism during different infection stages and could inform targeted therapeutic approaches.

How does temperature affect the expression and activity of UbiB in Y. pestis, and what are the implications for pathogenesis?

Temperature is a critical regulatory factor for UbiB expression and activity in Y. pestis, with significant implications for pathogenesis:

Temperature-Dependent Expression:

• UbiB expression is upregulated at 37°C (mammalian host temperature) compared to 26°C (flea vector temperature)

• Transcriptomic differences between wild-type and mutant strains at different temperatures reveal that genes related to ubiquinone synthesis show temperature-dependent regulation

• Similar to recombinant F1 antigen production, which is minimal at 27°C but increases significantly at 37°C, UbiB exhibits temperature-dependent expression patterns

Enzymatic Activity Changes:

• The ATPase activity of UbiB shows temperature optimum around 37°C

• Stability of UbiB decreases at higher temperatures, requiring specialized chaperones

• The oxygen-dependent pathway involving UbiB becomes more active at mammalian host temperatures

Metabolic Implications:

• Temperature shift from flea to mammal triggers metabolic reprogramming

• UbiB-dependent ubiquinone biosynthesis increases to support higher energy demands

• The transition between oxygen-dependent and oxygen-independent pathways is influenced by temperature

Pathogenesis Connection:

• Temperature-dependent regulation of UbiB coordinates with other virulence factors

• The shift to 37°C triggers expression of both metabolic adaptations and virulence genes

• This coordinated response optimizes Y. pestis metabolism for survival in the mammalian host

Experimental Evidence:

• When expressed recombinantly, the temperature dependence is preserved, with higher expression at 37°C compared to 27°C

• This pattern mimics other temperature-regulated proteins in Y. pestis, indicating a common regulatory mechanism

Understanding this temperature-dependent regulation provides insight into how Y. pestis transitions between vector and host environments, which could inform the development of temperature-sensitive therapeutic strategies targeting metabolic vulnerabilities.

What experimental approaches can be used to investigate the role of UbiB in Y. pestis adaptation to varying oxygen environments?

Investigating UbiB's role in Y. pestis adaptation to varying oxygen environments requires multiple experimental approaches:

1. Genetic Manipulation Studies:

• Creation of precise ubiB deletion mutants using CRISPR-Cas9 or allelic exchange

• Construction of conditional expression strains (e.g., using rhamnose-inducible promoters)

• Generation of double mutants lacking both O2-dependent (UbiB) and O2-independent (UbiU/UbiV) pathways

2. Transcriptomic Profiling:

• RNA-seq analysis of wild-type vs. ubiB mutants across oxygen gradients

• Identification of compensatory gene expression changes

• Time-course analysis during transition between aerobic and anaerobic conditions

3. Metabolomic Analyses:

• Quantification of ubiquinone and intermediates using HPLC-MS

• Metabolic flux analysis using 13C-labeled precursors

• Comparison of metabolite profiles between wild-type and ubiB mutants

4. Physiological Characterization:

• Growth curves under varying oxygen concentrations

• Survival assays in oxygen-limited environments

• Measurement of cellular respiration rates and membrane potential

5. Host-Relevant Models:

• Macrophage infection assays comparing wild-type and ubiB mutants

• Tissue culture systems with controlled oxygen gradients

• In vivo oxygen measurement during infection using oxygen-sensitive probes

6. Biochemical Approaches:

• In vitro reconstitution of ubiquinone biosynthesis under varying oxygen tensions

• Enzyme kinetics studies with purified recombinant UbiB

• Assessment of protein-protein interactions as oxygen levels change

7. Evolutionary Analyses:

• Comparative genomics of UbiB across Yersinia species with different ecological niches

• Identification of selective pressures on ubiB genes

• Analysis of UbiB conservation in facultative vs. obligate aerobes/anaerobes

These approaches collectively provide a comprehensive understanding of how UbiB contributes to Y. pestis metabolic flexibility across oxygen gradients, which is crucial during transmission and infection .

What are the potential off-target effects when using UbiB inhibitors as antimicrobial agents against Y. pestis?

When developing UbiB inhibitors as antimicrobial agents against Y. pestis, several potential off-target effects must be considered:

Impacts on Host Ubiquinone Biosynthesis:

• Mammalian ubiquinone biosynthesis involves COQ8A and COQ8B, which share homology with bacterial UbiB

• Inhibitors targeting conserved active sites could affect host mitochondrial function

• Potential consequences include decreased ATP production, increased oxidative stress, and mitochondrial dysfunction

Effects on Commensal Microbiota:

• Many commensal bacteria rely on ubiquinone for respiration

• Broad-spectrum UbiB inhibitors could disrupt gut microbiome composition

• Secondary effects might include dysbiosis and associated immune/metabolic disturbances

Alternate Bacterial Targets:

• Cross-reactivity with other bacterial kinases or ATPases

• Potential inhibition of essential bacterial processes beyond ubiquinone biosynthesis

• Unintended effects on bacterial cell division, DNA replication, or protein synthesis

Resistance Development Concerns:

• Selection pressure on the oxygen-independent pathway (UbiU/UbiV)

• Compensatory mutations in other ubiquinone biosynthesis genes

• Potential for cross-resistance to other antimicrobials

Toxicity Considerations:

• Xenobiotic metabolism of inhibitors may generate toxic metabolites

• Accumulation of ubiquinone precursors could have toxic effects

• Potential immunomodulatory effects of altered bacterial metabolism

Mitigation Strategies:

• Structure-based design focusing on bacterial-specific features of UbiB

• Careful assessment of selectivity against mammalian homologs

• Combined targeting of both oxygen-dependent and oxygen-independent pathways

• Development of Y. pestis-specific delivery systems

• Thorough toxicological evaluation in mammalian systems

These considerations are critical for developing UbiB inhibitors with acceptable safety profiles while maintaining efficacy against Y. pestis, particularly given the importance of mitochondrial function in mammalian hosts.

How do post-translational modifications affect the function of UbiB in Yersinia pestis compared to recombinant UbiB expressed in E. coli?

Post-translational modifications (PTMs) significantly impact UbiB function, with important differences between native Y. pestis UbiB and recombinant versions expressed in E. coli:

Types of PTMs in Native UbiB:

• Phosphorylation at serine/threonine residues affecting kinase activity

• Possible redox-sensitive modifications of cysteine residues

• Potential iron-sulfur cluster incorporation influencing protein stability

• N-terminal processing that may affect localization or activity

Differences in Recombinant Expression:

• E. coli expression systems may lack specific kinases or modification enzymes present in Y. pestis

• Overexpression can overwhelm native PTM machinery, resulting in incomplete modifications

• N-terminal His-tag addition may block certain modifications or alter protein folding

• Expression temperature affects PTM efficiency (37°C vs. lower temperatures)

Functional Consequences:

• Altered catalytic efficiency of recombinant vs. native UbiB

• Different stability profiles under varying environmental conditions

• Changed protein-protein interaction capabilities

• Modified regulatory responses to cellular signals

Detection and Characterization Methods:

• Mass spectrometry to identify and quantify PTMs

• Site-directed mutagenesis to assess functional significance

• Comparison of enzyme kinetics between native and recombinant forms

• Proteomic analysis under different growth conditions

Strategies for Authentic Recombinant Production:

• Co-expression with relevant Y. pestis modification enzymes

• Use of cell-free systems supplemented with Y. pestis extracts

• Development of Y. pseudotuberculosis (close relative) expression systems

• Site-specific incorporation of modifications using chemical biology approaches

Understanding these differences is critical for accurate functional characterization of UbiB and for developing inhibitors that effectively target the native protein in its physiological context.

What are the evolutionary implications of UbiB conservation across Yersinia species and its relationship to pathogenicity?

The evolutionary conservation of UbiB across Yersinia species provides valuable insights into its relationship with pathogenicity:

Phylogenetic Analysis:

• UbiB is highly conserved across all Yersinia species, including pathogenic (Y. pestis, Y. pseudotuberculosis, Y. enterocolitica) and environmental species

• Sequence similarity analysis reveals >90% identity among pathogenic Yersinia UbiB proteins

• The high conservation suggests essential metabolic functions predating pathogen evolution

Evolutionary Pressure:

• The ubiB gene shows evidence of purifying selection, indicating functional constraints

• Adaptive evolution appears minimal compared to virulence factors

• Conservation extends to the wider Enterobacteriaceae family, suggesting ancient origins

Relationship to Pathogenicity Evolution:

• While UbiB itself is not a virulence factor, its role in metabolism supports pathogenicity

• Y. pestis evolved from Y. pseudotuberculosis approximately 1,500-20,000 years ago, maintaining UbiB while acquiring specific virulence factors

• The preservation of both oxygen-dependent (UbiB) and oxygen-independent ubiquinone biosynthesis pathways enables adaptation to diverse host environments

Genomic Context:

• Comparative genomics reveals that ubiB is chromosomally encoded in all Yersinia species

• Unlike virulence factors often found on pathogenicity islands or plasmids, ubiB remains in the core genome

• Gene neighborhood analysis shows conserved operonic structure across species

Host Adaptation Implications:

• The maintenance of UbiB alongside the evolution of the oxygen-independent pathway represents a key metabolic adaptation

• This dual-pathway system allows colonization of hosts with varying oxygen gradients

• The ability to synthesize ubiquinone under all oxygen conditions likely contributed to Y. pestis' exceptional pathogenicity

This evolutionary perspective demonstrates how fundamental metabolic functions like UbiB provide the foundation upon which pathogen-specific virulence mechanisms can evolve and operate .

How does the recombinant expression of UbiB compare methodologically to the expression of other Y. pestis virulence factors?

The recombinant expression of UbiB presents distinct methodological challenges and considerations compared to well-studied Y. pestis virulence factors:

Comparison with F1 Antigen Expression:

• F1 capsular antigen (Caf1) is extensively expressed recombinantly for vaccine development

• While F1 is efficiently expressed in both E. coli and yeast systems , UbiB expression often results in lower yields

• F1 expression shows strong temperature dependence (minimal at 27°C, significant at 37°C) , a feature also observed with UbiB

• F1 is secreted and forms capsular fibers, whereas UbiB is intracellular with potential membrane association

Comparison with LcrV Expression:

• LcrV (V antigen) is a well-established recombinant expression target for plague vaccines

• Unlike LcrV, which can be readily expressed as soluble protein, UbiB often forms inclusion bodies

• LcrV-based fusion proteins show enhanced stability and immunogenicity , a strategy that might improve UbiB solubility

Expression System Considerations:

Functional Validation Methods:

• UbiB requires enzymatic activity assays, unlike F1/LcrV where immunological recognition is sufficient

• Structural integrity assessment for UbiB involves thermal stability and ATP binding

• F1 and LcrV functionality can be verified through immunization studies, whereas UbiB requires biochemical assays

These methodological differences reflect the distinct cellular roles and biochemical properties of UbiB compared to classical virulence factors, necessitating tailored expression and purification strategies for successful recombinant production .

What role does UbiB play in the adaptation of Y. pestis to different environmental stress conditions beyond oxygen variation?

UbiB contributes to Y. pestis adaptation to multiple environmental stressors beyond oxygen variation:

Temperature Stress Response:

• UbiB-dependent ubiquinone biosynthesis is critical during temperature transitions from flea (26°C) to mammalian host (37°C)

• Increased ubiquinone production supports higher metabolic demands during thermal stress

• UbiB activity helps maintain membrane integrity during temperature fluctuations

Oxidative Stress Adaptation:

• Ubiquinone functions as an antioxidant in bacterial membranes

• UbiB-dependent ubiquinone biosynthesis provides protection against reactive oxygen species (ROS)

• This becomes particularly important during host-generated oxidative burst in macrophages and neutrophils

Iron Limitation Response:

• Iron acquisition systems are linked to energy metabolism

• UbiB-dependent respiration supports the energetically expensive process of iron uptake

• Studies show that iron supplementation can restore virulence in metabolic mutants, suggesting a connection between UbiB-dependent metabolism and iron acquisition

pH Stress Management:

• Ubiquinone contributes to proton motive force maintenance under acidic conditions

• UbiB activity supports adaptation to varying pH environments encountered during infection

• The ability to maintain energy production in acidified phagosomes may contribute to intracellular survival

Nutrient Limitation Adaptation:

• UbiB-dependent respiration provides efficient energy harvesting during nutrient limitation

• The electron transport chain enables Y. pestis to utilize diverse carbon sources efficiently

• Metabolic flexibility supported by ubiquinone biosynthesis allows adaptation to changing nutrient availability

Antibiotic Stress Response:

• Some antibiotic resistance mechanisms require energy-dependent efflux pumps

• UbiB-supported respiration provides energy for these resistance mechanisms

• Metabolic adaptations involving UbiB may contribute to persistence during antibiotic exposure

These diverse roles in stress adaptation highlight why UbiB and ubiquinone biosynthesis are maintained across Yersinia species despite the energetic cost, as they provide crucial adaptability in the challenging and variable environments encountered during the complex life cycle of Y. pestis .

How can advanced protein engineering techniques be applied to improve the stability and activity of recombinant UbiB for research applications?

Advanced protein engineering offers several strategies to enhance recombinant UbiB stability and activity:

1. Computational Design Approaches:

• Identification of destabilizing residues using Rosetta or FoldX algorithms

• In silico prediction of stabilizing mutations

• Modeling of protein dynamics to identify flexible regions contributing to instability

• Design of disulfide bonds to rigidify the structure

2. Directed Evolution Strategies:

• Error-prone PCR to generate UbiB variant libraries

• Screening for thermostable variants using survival at elevated temperatures

• Selection systems coupling UbiB activity to cell survival

• Deep mutational scanning to comprehensively map stability effects

3. Domain-Based Engineering:

• Creation of chimeric proteins incorporating stable domains from homologous proteins

• Truncation variants removing flexible termini

• Domain insertion of stabilizing elements at flexible loops

• Circular permutation to optimize domain orientation

4. Surface Engineering:

• Introduction of surface-exposed charged residues to enhance solubility

• Reduction of surface hydrophobicity to minimize aggregation

• PEGylation of specific residues to improve stability

• Super-charging approaches to increase electrostatic repulsion

5. Fusion Partner Optimization:

• Systematic testing of solubility-enhancing fusion partners (MBP, SUMO, Trx)

• Design of optimized linkers between UbiB and fusion partners

• Development of novel fusion systems specifically tailored for ATPases

• Split-intein approaches for tag removal without proteases

6. Cofactor Binding Enhancement:

• Engineering improved ATP binding pockets

• Optimization of metal coordination sites

• Introduction of stabilizing interactions with cofactors

• Selection for variants with higher cofactor affinity

7. Practical Implementation Strategy:

These approaches can be combined in iterative cycles of design, testing, and refinement to develop optimized UbiB variants with significantly improved properties for research applications.

What insights can comparative analysis of UbiB across different bacterial pathogens provide for antimicrobial development?

Comparative analysis of UbiB across bacterial pathogens offers valuable insights for antimicrobial development:

Sequence and Structural Conservation:

• UbiB homologs show varying degrees of conservation across pathogens

• Critical catalytic residues are typically highly conserved

• Variable regions may present opportunities for species-selective targeting

• Structural modeling reveals pathogen-specific binding pockets near the active site

Functional Divergence:

• Different pathogens show varying dependence on UbiB for virulence

• Some bacteria possess functional redundancy in ubiquinone biosynthesis

• Obligate aerobes rely more heavily on UbiB than facultative anaerobes

• Metabolic network analysis reveals pathogen-specific vulnerabilities

Regulatory Variations:

• Expression control mechanisms differ between bacterial species

• Some pathogens upregulate UbiB specifically during infection

• Stress-responsive elements in the ubiB promoter vary across species

• Post-translational regulation shows species-specific patterns

Cross-Species Inhibition Potential:

• Broad-spectrum inhibitors targeting highly conserved regions

• Narrow-spectrum approaches exploiting pathogen-specific features

• Combination strategies targeting both conserved and variable regions

• Synergistic opportunities with existing antibiotics

Resistance Development Patterns:

• Different bacterial species show varying propensity for developing resistance

• Alternative metabolic pathways available in some pathogens but not others

• Genetic barriers to resistance vary across bacterial species

• Evolutionary constraints may limit certain resistance mechanisms

Therapeutic Implications:

• Priority pathogens where UbiB represents a particularly vulnerable target

• Potential for repurposing existing compounds that inadvertently target UbiB

• Structure-guided design of inhibitors with tailored spectrum of activity

• Development of species-selective diagnostic tools based on UbiB variations

This comparative approach not only guides the rational design of UbiB inhibitors but also helps predict their likely efficacy and resistance profiles across different bacterial pathogens, potentially leading to more targeted antimicrobial strategies.

What are the latest methodological advances in studying the interaction between UbiB and other components of the ubiquinone biosynthesis pathway?

Recent methodological advances have significantly enhanced our ability to study UbiB interactions with other ubiquinone biosynthesis components:

1. Advanced Structural Biology Techniques:

• Cryo-electron microscopy for visualization of UbiB-containing protein complexes

• Integrative structural biology combining X-ray crystallography, NMR, and computational modeling

• Hydrogen-deuterium exchange mass spectrometry (HDX-MS) to map protein-protein interaction interfaces

• Single-particle analysis of reconstituted ubiquinone biosynthesis complexes

2. Protein-Protein Interaction Technologies:

• Chemical crosslinking coupled with mass spectrometry (XL-MS) to capture transient interactions

• Proximity-dependent biotin labeling (BioID, TurboID) to identify interacting partners in vivo

• Förster resonance energy transfer (FRET) sensors to visualize interactions in real-time

• Surface plasmon resonance with engineered sensor chips for quantitative binding analysis

3. Systems Biology Approaches:

• Metabolic flux analysis using stable isotope labeling to trace ubiquinone precursors

• Protein correlation profiling across fractionated cell extracts

• Global genetic interaction mapping using CRISPRi to identify synthetic interactions

• Multi-omics integration connecting transcriptomics, proteomics, and metabolomics data

4. Advanced Microscopy Methods:

• Super-resolution microscopy to visualize UbiB localization relative to other pathway components

• Single-molecule tracking to monitor dynamic interactions

• Correlative light and electron microscopy to connect molecular interactions with cellular ultrastructure

• Lattice light-sheet microscopy for long-term imaging of protein dynamics

5. Computational Methods:

• Molecular dynamics simulations of multi-protein complexes

• Machine learning approaches to predict protein-protein interactions

• Coevolutionary analysis to identify interacting surfaces

• Integrative modeling incorporating sparse experimental constraints

6. Innovative Biochemical Approaches:

• Nanodisc reconstitution systems for membrane-associated components

• Cell-free expression systems for rapid testing of interaction hypotheses

• Activity-based protein profiling to capture functional interactions

• Native mass spectrometry to determine composition of intact complexes

These methodological advances collectively enable a more comprehensive understanding of how UbiB functions within the broader context of ubiquinone biosynthesis, providing opportunities for targeted intervention in this critical metabolic pathway .

How might the functions of UbiB in Y. pestis inform therapeutic strategies against other Gram-negative pathogens?

Insights from UbiB in Y. pestis can inform broader therapeutic strategies against Gram-negative pathogens:

Common Vulnerabilities in Energy Metabolism:

• UbiB function in ubiquinone biosynthesis represents a conserved vulnerability across many Gram-negative pathogens

• Comparative genomics reveals UbiB is essential in multiple priority pathogens including Pseudomonas aeruginosa, Acinetobacter baumannii, and Escherichia coli

• The essentiality of UbiB under aerobic conditions provides a conditional targeting opportunity

Dual-Pathway Targeting Strategy:

• The discovery of oxygen-dependent (UbiB) and oxygen-independent (UbiU/UbiV) pathways in Y. pestis suggests similar redundancy may exist in other pathogens

• Simultaneous targeting of both pathways could overcome metabolic plasticity

• This approach may be particularly effective against pathogens that encounter varying oxygen levels during infection

Drug Development Implications:

• Structure-activity relationships developed for Y. pestis UbiB inhibitors may translate to homologs in other species

• Screening approaches used for Y. pestis UbiB can be adapted for other Gram-negative pathogens

• The potential for developing narrow or broad-spectrum inhibitors based on UbiB conservation patterns

Overcoming Resistance Mechanisms:

• Understanding how Y. pestis might develop resistance to UbiB inhibitors informs strategies for other pathogens

• Targeting metabolic bottlenecks may impose higher barriers to resistance evolution

• Combination therapies involving UbiB inhibitors could enhance effectiveness of existing antibiotics

Clinical Applications Beyond Plague:

• Potential applications in treating infections by multidrug-resistant Gram-negative bacteria

• Prophylactic use in high-risk settings where conventional antibiotics are compromised by resistance

• Development of narrow-spectrum therapies for targeted pathogen elimination while preserving microbiome

Research Priorities:

• Comparative analysis of UbiB essentiality across priority pathogens

• Evaluation of oxygen-dependent vs. oxygen-independent pathway utilization in different infection contexts

• Structure-based design of inhibitor series with defined spectrum of activity

• Assessment of resistance development in diverse Gram-negative species