Recombinant Tolumonas auensis Probable ubiquinone biosynthesis protein UbiB (ubiB)

What is the Tolumonas auensis UbiB protein and what is its primary function?

The UbiB protein from Tolumonas auensis is classified as a probable ubiquinone biosynthesis protein. It plays a critical role in the biosynthetic pathway leading to ubiquinone (coenzyme Q) production, which is essential for electron transport in cellular respiration. The full-length protein consists of 543 amino acids and has been recombinantly expressed with an N-terminal His tag in E. coli expression systems .

Tolumonas auensis is a gram-negative, rod-shaped bacterium belonging to the Gammaproteobacteria class, first isolated from anoxic sediments of a freshwater lake. The organism is known to produce major lipoquinones including ubiquinone 8 and menaquinone 8 under both oxic and anoxic growth conditions, highlighting the importance of UbiB in its metabolism .

How does Tolumonas auensis UbiB differ from UbiB proteins in other bacterial species?

Tolumonas auensis UbiB belongs to a larger family of UbiB proteins involved in ubiquinone biosynthesis across various bacterial species. While maintaining core functional domains, the T. auensis UbiB has unique features that distinguish it from homologs in other organisms.

Comparative analysis reveals that T. auensis, as a member of the Aeromonadaceae family within Gammaproteobacteria, possesses UbiB with specific adaptations that may reflect its ecological niche . Unlike some other bacterial species, T. auensis can thrive under both aerobic and anaerobic conditions, producing ubiquinone 8 and menaquinone 8 regardless of oxygen availability, which suggests its UbiB may function efficiently in varied redox environments .

When compared to the related species Tolumonas lignolytica, which has a distinct metabolic capacity for lignin degradation, the UbiB protein likely contributes to different metabolic pathways despite sharing core ubiquinone biosynthesis functions .

What are the structural characteristics of the UbiB protein that contribute to its function in ubiquinone biosynthesis?

The UbiB protein from Tolumonas auensis contains several structural features that contribute to its presumed enzymatic activity in ubiquinone biosynthesis:

• Domain architecture analysis indicates the presence of a kinase-like domain characteristic of the UbiB protein family, suggesting ATP-dependent enzymatic activity.

• The protein contains conserved motifs essential for substrate binding and catalysis, including regions for interaction with ubiquinone precursors.

• Secondary structure predictions suggest a mix of alpha-helical and beta-sheet regions forming a globular protein with specific binding pockets.

The protein likely functions as part of a larger enzymatic complex in the ubiquinone biosynthetic pathway, with specific interaction sites for other pathway components .

What experimental approaches are most effective for assessing UbiB protein activity in vitro?

For effective assessment of Tolumonas auensis UbiB protein activity in vitro, researchers should consider the following methodological approaches:

• Enzymatic activity assays: Since UbiB is involved in ubiquinone biosynthesis, activity can be measured using:

  • ATP consumption assays to monitor kinase activity

  • HPLC analysis to detect transformation of ubiquinone precursors

  • Coupled enzyme assays that link UbiB activity to detectable signals

• Binding assays: Isothermal titration calorimetry (ITC) or surface plasmon resonance (SPR) can determine binding affinities between purified UbiB and potential substrates or cofactors.

• Structural biology approaches: X-ray crystallography or cryo-EM to determine three-dimensional structure, providing insights into catalytic mechanisms.

• Reconstitution experiments: Integrating purified UbiB into liposomes or nanodiscs to mimic native membrane environments, which may be critical for proper function.

The recombinant His-tagged protein expressed in E. coli provides an excellent starting material for these analyses. Researchers should reconstitute the lyophilized protein according to the manufacturer's recommendations, typically in Tris-based buffer at concentrations of 0.1-1.0 mg/mL with added glycerol for stability .

How does the metabolic context of Tolumonas auensis influence UbiB function and ubiquinone biosynthesis?

The metabolic versatility of Tolumonas auensis creates a unique context for UbiB function:

• Dual respiratory capabilities: T. auensis can grow under both oxic and anoxic conditions, producing ubiquinone 8 and menaquinone 8 in both environments. This suggests that UbiB must function efficiently regardless of oxygen availability, potentially through regulatory mechanisms that maintain ubiquinone biosynthesis under varying redox conditions .

• Specialized toluene production: T. auensis has the distinctive ability to produce toluene from phenylalanine, phenylpyruvate, phenyllactate, and phenylacetate, which may create unique metabolic intermediates that interact with ubiquinone-dependent pathways. This metabolic feature requires coordination between aromatic compound metabolism and electron transport systems where ubiquinone functions .

• Carbon source adaptation: T. auensis produces acetate, ethanol, and formate as major fermentation products when grown on glucose. The energy generation from these pathways is likely dependent on functional ubiquinone, suggesting that UbiB activity may be regulated according to carbon source availability .

The interaction between these metabolic pathways and ubiquinone biosynthesis represents an important area for future research, particularly regarding how UbiB activity might be modulated under different growth conditions.

What are the optimal conditions for expressing and purifying recombinant Tolumonas auensis UbiB protein?

Based on established protocols for the recombinant production of Tolumonas auensis UbiB protein, the following methodological guidelines are recommended:

Expression System:

• Host: E. coli (BL21 or similar expression strains)

• Vector: pET-based or similar with N-terminal His-tag fusion

• Induction: IPTG concentration typically 0.5-1.0 mM

• Temperature: 16-20°C post-induction to enhance solubility

• Duration: 16-20 hours post-induction

Purification Protocol:

• Cell lysis: Sonication or pressure-based methods in Tris-based buffer (pH 8.0) containing protease inhibitors

• Initial purification: Ni-NTA affinity chromatography with imidazole gradient elution

• Secondary purification: Size exclusion chromatography to remove aggregates

• Final preparation: Concentration and buffer exchange to Tris/PBS-based buffer, pH 8.0

Storage Recommendations:

• For short-term: Store at 4°C (up to one week)

• For long-term: Add 50% glycerol and store at -20°C/-80°C in small aliquots to avoid repeated freeze-thaw cycles

• Lyophilization option: The protein can be lyophilized for extended storage stability

The purified protein should achieve >90% purity as determined by SDS-PAGE for optimal experimental reliability .

What analytical techniques are recommended for studying UbiB-mediated ubiquinone biosynthesis in Tolumonas auensis?

To comprehensively study UbiB-mediated ubiquinone biosynthesis in Tolumonas auensis, researchers should employ multiple complementary analytical techniques:

• Chromatographic Analysis:

  • HPLC with electrochemical detection for quantification of ubiquinone and intermediates

  • LC-MS/MS for identification of pathway intermediates and modified precursors

  • TLC for rapid screening of lipid-soluble pathway components

• Isotopic Labeling:

  • 13C-labeled precursors to track carbon flow through the ubiquinone pathway

  • 18O-labeling to determine oxygen incorporation steps

  • Pulse-chase experiments to determine pathway kinetics

• Genetic Approaches:

  • Targeted gene knockouts or CRISPR interference to assess the impact of UbiB deficiency

  • Complementation studies with wild-type or mutant UbiB to establish structure-function relationships

  • Transcriptomics to identify co-regulated genes in the biosynthetic pathway

• Biochemical Assays:

  • In vitro reconstitution of the ubiquinone biosynthetic pathway with purified components

  • Enzyme kinetics studies to determine Km and Vmax values for UbiB with various substrates

  • Protein-protein interaction studies to identify partners in the biosynthetic machinery

The catalase and peroxidase activities observed in Tolumonas species provide additional experimental targets for understanding the relationship between reactive oxygen species management and ubiquinone biosynthesis .

How can researchers effectively analyze the relationship between UbiB function and the unique metabolic capabilities of Tolumonas auensis?

To investigate the relationship between UbiB function and Tolumonas auensis metabolism, researchers should implement the following integrated experimental approach:

• Comparative Growth Studies:

  • Culture T. auensis under varying oxygen tensions, monitoring ubiquinone content and UbiB expression

  • Assess growth with different carbon sources to determine effects on ubiquinone production

  • Compare growth characteristics between wild-type and UbiB-deficient strains

• Metabolic Flux Analysis:

  • Employ 13C-metabolic flux analysis to trace carbon flow between central metabolism and ubiquinone biosynthesis

  • Measure changes in electron transport chain activity under different growth conditions

  • Quantify relationships between toluene production pathways and ubiquinone biosynthesis

• Stress Response Experiments:

  • Challenge cultures with oxidative stress and assess UbiB expression and ubiquinone production

  • Examine the role of UbiB in adaptation to environmental stressors relevant to T. auensis' natural habitat

  • Evaluate peroxidase and catalase activities in relation to UbiB function

• Systems Biology Integration:

  • Combine transcriptomics, proteomics, and metabolomics data to create network models

  • Identify regulatory connections between UbiB, ubiquinone biosynthesis, and unique metabolic features

  • Compare with related species like T. lignolytica to understand evolutionary adaptations

This integrated approach will help elucidate how UbiB function is coordinated with T. auensis' ability to produce toluene and thrive in both oxic and anoxic environments .

How can structural biology approaches enhance our understanding of Tolumonas auensis UbiB functional mechanisms?

Structural biology techniques can provide critical insights into the functional mechanisms of Tolumonas auensis UbiB:

• X-ray Crystallography Protocol:

  • Express His-tagged UbiB in large quantities (10-20 mg)

  • Employ sparse matrix screening to identify initial crystallization conditions

  • Optimize conditions focusing on pH ranges of 7.0-8.0 (near the protein's native environment)

  • Consider co-crystallization with ATP analogs, substrate mimics, or interaction partners

  • Analyze diffraction patterns at 2.0 Å resolution or better to identify catalytic sites

• Cryo-EM Analysis:

  • Particularly valuable if UbiB functions in a larger protein complex

  • Prepare samples in Tris-based buffers with minimal glycerol

  • Use negative staining for initial assessment followed by vitrification

  • Apply single-particle analysis to reconstruct 3D structure

  • Focus on conformational changes upon substrate binding

• NMR Spectroscopy for Dynamics:

  • Express isotopically labeled protein (15N, 13C)

  • Perform HSQC experiments to monitor conformational changes

  • Analyze chemical shift perturbations upon ligand binding

  • Map the protein's dynamic regions relevant to catalytic activity

• Computational Integration:

  • Apply molecular dynamics simulations based on structural data

  • Perform in silico docking with potential substrates

  • Identify conserved residues through evolutionary coupling analysis

  • Generate testable hypotheses about structure-function relationships

These approaches can reveal how UbiB's structure enables its function in the unique metabolic context of T. auensis, which produces both ubiquinone 8 and menaquinone 8 under varied oxygen conditions .

What strategies should be employed for investigating potential post-translational modifications of UbiB and their impact on function?

A comprehensive approach to investigating post-translational modifications (PTMs) of Tolumonas auensis UbiB should include:

• Mass Spectrometry-Based PTM Mapping:

  • Sample preparation: Purify UbiB from both recombinant systems and native T. auensis

  • Enzymatic digestion: Use multiple proteases (trypsin, chymotrypsin) to ensure complete coverage

  • LC-MS/MS analysis: Implement neutral loss scanning for phosphorylation

  • Data analysis: Apply PTM-specific search algorithms with false discovery rate control

• Site-Directed Mutagenesis of PTM Sites:

  • Generate alanine substitutions at identified PTM sites

  • Create phosphomimetic mutations (S/T to D/E) to simulate phosphorylation

  • Express and purify mutant proteins using established protocols

  • Compare enzymatic activities between wild-type and mutant variants

• In Vitro Modification Assays:

  • Incubate purified UbiB with potential modifying enzymes (kinases, acetylases)

  • Monitor modification using radioactive labeling or antibody detection

  • Assess functional consequences through activity assays

  • Identify conditions that promote or inhibit modifications

• Temporal Dynamics of PTMs:

  • Examine PTM patterns across growth phases

  • Compare modifications under aerobic versus anaerobic conditions

  • Assess PTM changes in response to metabolic shifts

  • Correlate PTM status with ubiquinone production levels

This methodological framework will provide insights into how post-translational modifications might regulate UbiB activity in response to T. auensis' metabolic needs, particularly during transitions between oxygen availability conditions .

How can researchers utilize comparative genomics to better understand the evolutionary context of Tolumonas auensis UbiB?

To leverage comparative genomics for understanding the evolutionary context of Tolumonas auensis UbiB, researchers should implement the following comprehensive approach:

• Phylogenetic Analysis Protocol:

  • Collect UbiB homolog sequences across diverse bacterial phyla

  • Perform multiple sequence alignment using MUSCLE or MAFFT algorithms

  • Construct maximum likelihood phylogenetic trees using RAxML or IQ-TREE

  • Apply appropriate evolutionary models with bootstrap replication (n≥1000)

  • Map tree against 16S rRNA-based species phylogeny to identify horizontal gene transfer events

• Synteny and Gene Neighborhood Analysis:

  • Examine conservation of gene order around ubiB across related species

  • Identify co-evolving genes using correlation analysis of presence/absence patterns

  • Compare with T. lignolytica and other Aeromonadaceae to identify family-specific features

  • Analyze promoter regions for conserved regulatory elements

• Domain Architecture Comparison:

  • Analyze domain shuffling events in UbiB evolution

  • Identify lineage-specific insertions/deletions

  • Map functional domains to evolutionary age

  • Correlate domain conservation with known biochemical functions

• Selection Pressure Analysis:

  • Calculate dN/dS ratios across UbiB coding sequences

  • Identify sites under positive or purifying selection

  • Correlate selection patterns with functional domains

  • Compare selection pressures between aerobic and facultative anaerobic lineages

This approach will contextualize the T. auensis UbiB within its evolutionary history and provide insights into how its unique features relate to the organism's distinctive metabolic capabilities, including toluene production and facultative anaerobic growth .

What are the most promising approaches for elucidating the precise catalytic mechanism of Tolumonas auensis UbiB?

Future research on the catalytic mechanism of Tolumonas auensis UbiB should focus on these promising methodological approaches:

• Advanced Enzymology:

  • Transient kinetic analysis using stopped-flow spectrometry

  • Isotope effect studies to identify rate-limiting steps

  • Cryogenic electron paramagnetic resonance (EPR) to detect radical intermediates

  • Temperature-dependent kinetics to determine activation parameters

• Chemical Biology:

  • Activity-based protein profiling with mechanism-based probes

  • Crosslinking studies with substrate analogs to trap catalytic intermediates

  • Time-resolved mass spectrometry to detect transient reaction species

  • Unnatural amino acid incorporation to introduce spectroscopic probes at catalytic sites

• Structural Dynamics:

  • Time-resolved X-ray crystallography to capture catalytic intermediates

  • Hydrogen-deuterium exchange mass spectrometry to map conformational changes

  • Single-molecule FRET to monitor protein dynamics during catalysis

  • Vibrational spectroscopy to detect bond formation/breaking events

• Computational Enzymology:

  • Quantum mechanics/molecular mechanics (QM/MM) simulations of reaction mechanisms

  • Free energy calculations for proposed catalytic pathways

  • Machine learning approaches to integrate experimental data with computational models

  • Molecular dynamics simulations of substrate binding and product release

These approaches, when integrated, could definitively establish whether UbiB functions as a kinase as predicted, or has alternative catalytic activities in the ubiquinone biosynthetic pathway within the unique metabolic context of T. auensis .

How might engineered variants of UbiB be utilized to enhance understanding of ubiquinone biosynthesis or for biotechnological applications?

Engineered variants of Tolumonas auensis UbiB offer significant potential for both fundamental research and biotechnological applications:

• Structure-Function Analysis:

  • Systematic alanine scanning mutagenesis to map functional residues

  • Domain swapping with UbiB homologs to identify specificity determinants

  • Construction of chimeric proteins to dissect domain functions

  • Introduction of reporter groups at key positions to monitor conformational changes

• Pathway Engineering:

  • Overexpression of optimized UbiB variants to enhance ubiquinone production

  • Integration with other ubi genes to reconstruct complete biosynthetic pathways

  • Development of UbiB variants with altered substrate specificity

  • Creation of orthogonal biosynthetic pathways for novel quinone derivatives

• Biosensor Development:

  • Engineer UbiB-based FRET biosensors for ATP/ADP ratios

  • Develop activity-responsive reporter systems for high-throughput screening

  • Create whole-cell biosensors for ubiquinone precursors

  • Design immobilized enzyme systems for analytical applications

• Therapeutic Exploration:

  • Investigate UbiB as a potential target for antimicrobial development

  • Engineer UbiB variants that can complement human CoQ biosynthesis defects

  • Develop inhibitors specific to bacterial UbiB for selective antimicrobial action

  • Create stabilized UbiB variants for structure-based drug design

The recombinant expression system already established for T. auensis UbiB provides an excellent foundation for these engineering approaches. The lyophilized protein format allows for long-term storage and convenient distribution to research teams, facilitating collaborative engineering efforts .

What interdisciplinary approaches could best address the relationship between UbiB function and the ecological adaptations of Tolumonas auensis?

To comprehensively understand the relationship between UbiB function and Tolumonas auensis ecological adaptations, future research should pursue these interdisciplinary approaches:

• Ecological Systems Biology:

  • Sample T. auensis from natural freshwater sediment habitats

  • Apply metatranscriptomics to assess UbiB expression in situ

  • Compare laboratory cultures with natural populations

  • Correlate UbiB expression with environmental parameters (oxygen levels, carbon sources)

• Synthetic Ecology:

  • Construct defined microbial communities with T. auensis

  • Examine UbiB function in interspecies interactions

  • Develop microfluidic systems to simulate environmental gradients

  • Assess metabolic exchanges involving ubiquinone-dependent pathways

• Adaptive Laboratory Evolution:

  • Select for T. auensis populations under varying selective pressures

  • Track genomic changes in ubiB and related genes

  • Correlate adaptive mutations with fitness in specific environments

  • Reconstruct evolutionary trajectories using experimental phylogenetics

• Integrative Multi-omics:

  • Combine transcriptomics, proteomics, and metabolomics under relevant conditions

  • Map UbiB activity to environmental stress responses

  • Trace ubiquinone's role in T. auensis' unique abilities:

    • Toluene production from aromatic precursors

    • Growth under anaerobic conditions

    • Adaptation to fluctuating oxygen levels in sediment environments

This interdisciplinary framework will provide insights into how UbiB function contributes to T. auensis' ecological success in freshwater sediments and explain the evolutionary advantage of maintaining both ubiquinone 8 and menaquinone 8 production regardless of oxygen availability .