Recombinant Yersinia pestis Probable ubiquinone biosynthesis protein UbiB (ubiB)

What is the function of UbiB in Yersinia pestis?

UbiB is a probable ubiquinone biosynthesis protein in Yersinia pestis that participates in the electron transport chain. It is believed to play a crucial role in the biosynthesis of ubiquinone (coenzyme Q), a lipophilic molecule that functions primarily as an electron carrier in both prokaryotes and eukaryotes. While the specific catalytic function of UbiB remains to be fully characterized, it likely contributes to the aerobic respiratory metabolism of Y. pestis, similar to its role in related proteobacteria. UbiB is part of a biosynthetic pathway that involves multiple Ubi proteins working together to synthesize ubiquinone .

How is UbiB related to other ubiquinone biosynthesis proteins?

UbiB is one of several proteins involved in ubiquinone biosynthesis. In Escherichia coli, a closely related organism to Y. pestis, 11 proteins (UbiA to UbiJ and UbiX) participate in UQ biosynthesis. These proteins catalyze the functionalization (prenylation, decarboxylation, hydroxylation, and methylation) of the phenyl ring of the 4-hydroxybenzoate precursor. UbiB interacts with other components of the ubiquinone biosynthetic machinery, including UbiK, a protein that has been shown to interact with UbiB, UbiE, UbiF, UbiG, UbiH, UbiI, UbiJ, and UbiX. These interactions suggest that UbiB functions within a complex network of proteins involved in ubiquinone production .

What is the structure and sequence of Y. pestis UbiB?

The Recombinant Yersinia pestis UbiB from strain Pestoides F (UniProt accession number A4TR37) consists of 543 amino acid residues. The full amino acid sequence is:

MTPGELRRLYLIIRVFLSYGLDELIPNIRLTLPLRVGRHLFFWLSNRHKDKSLGERLRLA LQELGPVWIKFGQMMSTRRDLFPPNIADQLALLQDRVASFDGALARKHIEIAMGGALETW FDDFDSQALASASIAQVHTARLKENGKEVVLKVIRPDILPIIKADVRLMYRLAGWVPKLL PDGRRLRPREVVREYEKTLLDELLLREAANAIQLRRNFEDSPMLYPEVYSDYCRESVL VMERIYGIPVSDIAALEDQGTNMKLLAERGVQVFFTQVFRDSFFHADMHPGNIFVSYEHP HDPLYIGIDCGIVGSLNKADKRYLAENFIAFFNRDYRRVAELHVDSGWVPRDTNVEDFEF AIRTVCEPIFEKPLAEISFGHVLLNLFNTARRFNMEVQPQLVLLQKTLLYVEGLGRQLYP QLDLWTTAKPFLESWLRDQVGLPAVIRALKEKAPFWAEKFPELPELVYDSLQQHKLLQQS VEKLTIQIQGQQQRQGQSRYLFGVGATLLVSGTILFLADATEVSTGFIVAGALAWFIGWR RTC

The protein is stored in Tris-based buffer with 50% glycerol, optimized for stability and functionality in experimental settings .

How do aerobic and anaerobic conditions affect UbiB function in Y. pestis?

The function of UbiB in Y. pestis likely differs under aerobic versus anaerobic conditions, similar to other ubiquinone biosynthesis proteins. In E. coli, certain hydroxylases in the UQ biosynthetic pathway (UbiI, UbiF, and UbiH) use dioxygen as a co-substrate and are therefore active only in aerobic conditions. Under anaerobic conditions, alternative hydroxylases function in the pathway, though these have not been fully identified. Research suggests that UbiB may be particularly important for aerobic ubiquinone biosynthesis, while its role may be diminished or altered under anaerobiosis. This differential functionality is significant when studying Y. pestis, which encounters varying oxygen environments during its life cycle between mammalian hosts and flea vectors .

What experimental approaches are recommended for studying UbiB interactions with other proteins?

Several experimental approaches have proven effective for studying protein-protein interactions involving ubiquinone biosynthesis proteins:

• Bacterial Two-Hybrid System (BACTH): This method has successfully demonstrated interactions between UbiK and multiple Ubi proteins, including UbiB. The technique is based on functional complementation between adenylate cyclase fragments and can detect both direct and indirect interactions.

• Co-expression and Co-purification Assays: Fusing UbiB with an affinity tag (such as His6) and co-expressing it with potential interaction partners can reveal binding relationships. Subsequent purification on appropriate resin (e.g., nickel-nitrilotriacetic acid) followed by detection of co-eluted proteins can confirm interactions.

• Pull-down Assays: Fusion of UbiB to maltose-binding protein (MBP) allows for purification on amylose columns and detection of interacting partners.

• Yeast Two-Hybrid Systems: While bacterial systems may be preferred for bacterial proteins, yeast two-hybrid approaches can identify direct interactions and pinpoint specific interaction domains .

How does UbiB contribute to Y. pestis virulence and pathogenicity?

UbiB's contribution to Y. pestis virulence likely stems from its role in energy metabolism through ubiquinone biosynthesis. Ubiquinone is crucial for aerobic respiration, which Y. pestis relies on during certain stages of infection. Disruption of ubiquinone biosynthesis could potentially attenuate bacterial growth and survival in host environments. Y. pestis has a complex life cycle involving both mammalian hosts and flea vectors, requiring metabolic adaptability. The ubiquinone biosynthetic pathway may be particularly important during aerobic growth phases in the mammalian host. Research with related ubiquinone biosynthesis factors in Salmonella enterica has shown that disruption of this pathway can impair proliferation in macrophages and reduce virulence in mice, suggesting similar potential roles for UbiB in Y. pestis pathogenicity .

What mechanisms govern the regulation of UbiB expression in response to environmental stimuli?

The regulation of UbiB expression likely responds to several environmental factors, particularly oxygen availability. In E. coli, the expression of ubiquinone biosynthesis genes is regulated in response to aerobic/anaerobic transitions, suggesting similar mechanisms may exist in Y. pestis. Oxygen-dependent transcriptional regulators may control ubiB expression, possibly involving the ArcA/ArcB two-component system or the Fnr regulator, which are known to mediate anaerobic gene regulation in many bacteria.

Temperature shifts, which Y. pestis experiences when transitioning between flea vectors (≈26°C) and mammalian hosts (37°C), may also influence UbiB expression. This temperature-dependent regulation could be mediated through sigma factors or other transcriptional regulators. Additionally, nutrient availability and growth phase likely affect UbiB expression, as ubiquinone biosynthesis must be coordinated with cellular energy demands. Future research using transcriptomic approaches under varying environmental conditions would help elucidate these regulatory mechanisms .

How do mutations in UbiB affect ubiquinone biosynthesis and bacterial fitness?

Mutations in UbiB would likely disrupt ubiquinone biosynthesis, leading to decreased UQ8 levels and accumulation of biosynthetic intermediates such as octaprenylphenol (OPP). Similar effects have been observed in other ubi mutants. The impact on bacterial fitness would be context-dependent:

• Aerobic Growth: Significant growth defects would be expected under aerobic conditions, as ubiquinone is essential for aerobic respiration. Mutations could lead to reduced growth rates, decreased biomass yield, and potential metabolic perturbations.

• Anaerobic Growth: Milder effects might be observed under anaerobic conditions, as Y. pestis can utilize alternative electron acceptors.

• Host Infection: Reduced virulence in mammalian hosts would be anticipated, similar to what has been observed with ubiK mutations in Salmonella, which impair proliferation in macrophages and virulence in mice.

• Flea Colonization: Effects on flea colonization might be complex, as the insect midgut represents a unique microenvironment .

What is the evolutionary significance of UbiB conservation across pathogenic Yersinia species?

The conservation of UbiB across pathogenic Yersinia species reflects its fundamental role in bacterial energy metabolism. Comparative genomic analyses indicate that ubiquinone biosynthesis proteins are widely distributed among proteobacteria, including Yersinia species. This conservation suggests strong selective pressure to maintain functional ubiquinone biosynthesis.

Y. pestis evolved from Y. pseudotuberculosis relatively recently (within the past 20,000 years), acquiring new virulence mechanisms while losing others through genetic decay. The maintenance of functional UbiB through this evolutionary transition indicates its importance for bacterial fitness in the ecological niches occupied by Y. pestis.

The selective pressures maintaining UbiB likely relate to its role in aerobic respiration, which remains essential despite Y. pestis's adaptation to new transmission cycles and host environments. Examining UbiB sequence variations across Yersinia strains could provide insights into adaptive changes that might optimize ubiquinone biosynthesis for specific host environments or virulence strategies .

What purification strategies are most effective for recombinant Y. pestis UbiB?

Based on successful approaches with related proteins, the following purification strategy is recommended for recombinant Y. pestis UbiB:

• Expression System Selection: Use the T7 promoter-based pET expression system in E. coli BL21(DE3) for high-level expression.

• Affinity Tagging: Incorporate a hexahistidine (His6) tag, preferably at the N-terminus to avoid interfering with potential C-terminal functional domains.

• Two-Step Purification Protocol:

  • Initial purification using immobilized metal affinity chromatography (IMAC) on a His-Trap HP column

  • Secondary purification via size exclusion chromatography using a HiLoad 16/600 Superdex 200 column to separate oligomeric states and remove aggregates

• Buffer Optimization: Use Tris-based buffer with 50% glycerol for long-term storage at -20°C. For working solutions, reduce glycerol to 10% and add reducing agents like DTT or β-mercaptoethanol to prevent oxidation of cysteine residues.

• Quality Control: Assess protein purity by SDS-PAGE and confirm identity using Western blotting and/or mass spectrometry .

How can functional assays be designed to assess UbiB activity in ubiquinone biosynthesis?

Designing functional assays for UbiB requires consideration of its probable role in the ubiquinone biosynthetic pathway. Several complementary approaches are recommended:

• Genetic Complementation Assays:

  • Generate ubiB deletion mutants in Y. pestis or E. coli

  • Measure restoration of ubiquinone levels upon expression of recombinant UbiB

  • Quantify growth rates under aerobic conditions to assess functional complementation

• Ubiquinone Quantification:

  • Use HPLC coupled to electrochemical detection (HPLC-ECD) to measure UQ8 levels

  • Monitor at 275 nm for detection of ubiquinone and intermediates

  • Use mass spectrometry to identify accumulated intermediates (e.g., OPP at m/z 656.5 [M + NH4+])

• Enzyme Activity Assays:

  • While the specific enzymatic activity of UbiB remains unclear, assays could be designed based on proposed functions

  • Monitor kinase activity using radioactive ATP if UbiB functions as a kinase

  • Assess potential aerobic hydroxylase activity using appropriate substrates and oxygen consumption measurements

• Protein-Protein Interaction Analysis:

  • Use pull-down assays to identify interactions with other Ubi proteins

  • Apply bacterial two-hybrid systems to map the interaction network of UbiB within the ubiquinone biosynthesis machinery .

What approaches can be used to investigate the role of UbiB in Y. pestis virulence?

To investigate UbiB's role in Y. pestis virulence, a multi-faceted approach combining in vitro, ex vivo, and in vivo methods is recommended:

• Genetic Manipulation:

  • Generate precise ubiB deletion mutants in Y. pestis using allelic exchange

  • Create complemented strains expressing wildtype UbiB from a plasmid

  • Develop point mutations in conserved domains to identify critical residues

• In Vitro Growth Analysis:

  • Compare growth kinetics of wildtype and ΔubiB strains under various conditions

  • Test survival under oxidative stress, nutrient limitation, and varying temperatures

  • Measure ubiquinone levels to correlate with phenotypic changes

• Ex Vivo Infection Models:

  • Assess intracellular survival in macrophages using gentamicin protection assays

  • Measure bacterial replication rates in primary cells from relevant host species

  • Evaluate inflammatory responses through cytokine profiling

• In Vivo Virulence Assessment:

  • Determine the LD50 in appropriate animal models

  • Monitor bacterial dissemination to organs

  • Examine host immune responses to infection

• Flea Transmission Studies:

  • Evaluate the ability of ΔubiB mutants to colonize and form biofilms in fleas

  • Assess transmission efficiency from infected fleas to naive animals

  • Monitor bacterial persistence in the flea vector .

What are common challenges in expressing and purifying functional recombinant UbiB?

Several technical challenges can arise when working with recombinant Y. pestis UbiB:

• Protein Solubility Issues: UbiB may form inclusion bodies when overexpressed, particularly at high induction temperatures. To overcome this:

  • Lower the induction temperature to 16-18°C

  • Reduce IPTG concentration to 0.1-0.5 mM

  • Co-express with molecular chaperones (GroEL/GroES, DnaK/DnaJ/GrpE)

  • Use solubility-enhancing fusion tags like MBP or SUMO

• Protein Stability Concerns: UbiB may be prone to degradation or aggregation during purification. Strategies to improve stability include:

  • Include protease inhibitors in all buffers

  • Maintain samples at 4°C throughout purification

  • Add reducing agents to prevent oxidation of cysteine residues

  • Optimize buffer conditions with stabilizing agents like glycerol (50% for storage)

• Low Expression Yields: If expression levels are suboptimal:

  • Optimize codon usage for E. coli

  • Test different expression strains (BL21, C41/C43, Rosetta)

  • Evaluate different promoter systems

  • Consider auto-induction media for gentler expression

• Protein Activity Preservation: Maintaining functional activity through purification requires:

  • Avoiding harsh elution conditions

  • Testing activity after each purification step

  • Determining optimal storage conditions through stability tests

  • Considering the addition of cofactors or substrates during purification .

How does Y. pestis UbiB differ from homologous proteins in other bacterial species?

Y. pestis UbiB shares significant sequence similarity with homologous proteins from other proteobacteria, but with distinct characteristics that may reflect adaptation to the Y. pestis lifestyle:

What role does UbiB play in bacterial adaptation to different environmental niches?

UbiB contributes to bacterial adaptation across diverse environmental niches through its involvement in ubiquinone biosynthesis:

• Oxygen Availability Adaptation: UbiB's function appears particularly important under aerobic conditions, helping bacteria adapt to oxygen-rich environments. This is evident from studies of related ubiquinone biosynthesis proteins that show differential expression and activity between aerobic and anaerobic growth.

• Temperature Adaptation: Y. pestis must adapt to temperature shifts between mammalian hosts (37°C) and flea vectors (≈26°C). UbiB may contribute to this adaptation by ensuring appropriate ubiquinone production across temperature ranges, maintaining efficient electron transport chain function during host transitions.

• Nutrient Limitation Response: During infection, Y. pestis encounters nutrient-restricted environments. Efficient energy production through ubiquinone-dependent respiration may be crucial for survival under these conditions. UbiB's role in maintaining ubiquinone biosynthesis could be essential for bacterial persistence in nutrient-poor niches.

• Host Defense Evasion: Adaptation to oxidative stress generated by host immune responses requires robust electron transport systems. UbiB-dependent ubiquinone production may enhance bacterial resistance to oxidative damage, contributing to pathogen survival within phagocytes.

Understanding these adaptive functions of UbiB could provide insights into Y. pestis pathogenesis and potential vulnerabilities that might be exploited for therapeutic intervention .

What emerging technologies could advance our understanding of UbiB function?

Several cutting-edge technologies hold promise for elucidating UbiB function:

• Cryo-Electron Microscopy: High-resolution structural determination of UbiB alone and in complex with interaction partners could reveal functional domains and mechanisms of action. Recent advances in single-particle cryo-EM have made it possible to resolve structures of proteins previously resistant to crystallization.

• CRISPR-Cas9 Genome Editing: Precise genetic manipulation in Y. pestis using CRISPR-Cas9 could facilitate the generation of targeted ubiB mutations to assess structure-function relationships. This approach allows for scarless mutations and rapid generation of multiple variants.

• Native Mass Spectrometry: This technique could identify the stoichiometry and composition of UbiB-containing protein complexes under near-physiological conditions, providing insights into its functional interactions within the ubiquinone biosynthesis machinery.

• Metabolic Flux Analysis: Isotope labeling combined with quantitative metabolomics could track the flow of metabolites through the ubiquinone biosynthetic pathway in wildtype and ubiB mutant strains, revealing the specific biosynthetic step affected by UbiB.

• In Situ Structural Biology: Techniques like proximity labeling (BioID, APEX) could map the spatial organization of UbiB and its interacting partners within the bacterial cell, potentially revealing subcellular localization important for function .

How might UbiB research contribute to novel antimicrobial strategies?

Research on UbiB could inform new antimicrobial approaches through several avenues:

• Target Validation: Confirming UbiB's essentiality for Y. pestis virulence would validate it as a potential drug target. Experimental evidence demonstrating attenuated virulence in ubiB mutants would support this approach.

• Structure-Based Drug Design: Elucidation of UbiB's three-dimensional structure would enable rational design of small molecule inhibitors targeting specific functional domains or protein-protein interaction surfaces.

• Pathway-Specific Inhibitors: Understanding UbiB's precise role in the ubiquinone biosynthetic pathway could lead to development of inhibitors that specifically disrupt this essential metabolic process in pathogenic bacteria while sparing human cells.

• Species-Selective Targeting: Comparative analysis of UbiB across bacterial species could identify Y. pestis-specific features that might be exploited for selective inhibition, reducing potential impacts on beneficial microbiota.

• Combination Therapy Approaches: Insights into how UbiB inhibition affects bacterial physiology could inform strategies for synergistic drug combinations, potentially overcoming resistance mechanisms and enhancing treatment efficacy.

The involvement of UbiB in aerobic respiration suggests that inhibitors might be particularly effective against Y. pestis during its mammalian infection stage, potentially providing new options for plague treatment or prophylaxis .