Recombinant Pseudomonas entomophila Probable ubiquinone biosynthesis protein UbiB (ubiB)

What is the fundamental role of UbiB in ubiquinone biosynthesis in Pseudomonas species?

UbiB is a probable ubiquinone biosynthesis protein that plays a significant role in the O2-independent pathway of ubiquinone (UQ) production. In proteobacteria like Pseudomonas, UbiB functions as part of a complex with UbiU, UbiV, and UbiT proteins that enables ubiquinone synthesis under anaerobic conditions . While ubiquinone typically serves as the major electron carrier in aerobic respiration, the anaerobic synthesis pathway involving UbiB represents an important metabolic adaptation that allows bacteria to maintain electron transport chain functionality in oxygen-limited environments. Research indicates that while menaquinone (MK) and dimethyl-menaquinone (DMK) predominantly function in anaerobic respiratory chains, the division of labor between different quinones is not strictly defined, highlighting UbiB's importance in metabolic flexibility .

How does the genomic context of ubiB in P. entomophila compare to other Pseudomonas species?

The genomic context of ubiB varies significantly across Pseudomonas species, reflecting their diverse environmental adaptations. In P. entomophila, comparative genomic analysis reveals unique regulatory features not commonly found in other pseudomonads. For instance, while examining regulation patterns of membrane transporters in P. entomophila, researchers identified that certain genes can be placed under the control of specific regulons like the Pho regulon, which represents an atypical configuration across pseudomonads . Similar regulatory diversity likely exists for ubiB, which may be regulated differently in P. entomophila compared to closely related species. This variation in genomic context can be analyzed using complete annotated genomes from databases like MicroScope, which enable identification of species-specific transcription factors and regulatory elements .

What are the key structural features of UbiB that define its function in ubiquinone biosynthesis?

UbiB contains specific structural domains consistent with its role in ubiquinone biosynthesis, including ABC1/COQ8 kinase-like domain architecture. The protein features conserved kinase-like motifs that are essential for its function in the oxygen-independent ubiquinone biosynthesis pathway. Though not explicitly detailed in the provided sources, research on ubiquinone biosynthesis pathways indicates that UbiB likely works in conjunction with other Ubi-family proteins (UbiU, UbiV, and UbiT) to facilitate specific steps in the anaerobic ubiquinone biosynthesis pathway . Understanding these structural features is critical for experimental design when producing recombinant versions of the protein, as mutations in key domains could significantly alter protein functionality or stability.

What recombineering strategies are most effective for generating P. entomophila strains with modified ubiB expression?

For effective recombineering in Pseudomonas species, researchers should consider implementing the ReScribe system, which combines multiplex recombineering with CRISPR-Cas9 counterselection. Based on studies with P. putida, this approach significantly increases editing efficiency (approximately 10-fold) while reducing working time compared to standard recombineering methods . When modifying ubiB expression specifically, researchers should design 60 bp oligonucleotides with the desired mutation in the middle of the sequence, maintaining folding energy ≥16 kcal/mol which is suitable for Pseudomonas species with higher GC content .

For the experimental protocol, researchers should:

• Transform P. entomophila with pSEVA2514-recombinase-mutLE36KPP plasmid

• Grow cultures to OD600 of 0.5-0.7 and thermally induce recombinase expression (42°C, 10 min)

• Transform cells with the designed oligonucleotide (100 μM) targeting ubiB

• For higher efficiency, co-transform with pSEVAb62-ScCas9-crRNA_sp containing appropriate spacer sequences

• Apply multiple recombineering cycles if needed, with screening between cycles

This approach has demonstrated editing efficiencies of up to 90.5% for single-target edits and 77.8% for multiplex editing, making it suitable for precise ubiB modifications .

How can researchers effectively produce and purify recombinant P. entomophila UbiB for structural and functional studies?

Producing high-quality recombinant P. entomophila UbiB for structural and functional studies requires careful optimization of expression systems and purification protocols. Based on research with membrane-associated proteins in Pseudomonas species, the following methodological approach is recommended:

• Expression system selection:

  • For initial screening, test expression in both E. coli BL21(DE3) and specialized strains designed for membrane protein expression (C41, C43)

  • Evaluate Pseudomonas-specific expression systems if E. coli yields are poor

• Vector design optimization:

  • Include a removable His-tag or other affinity tag

  • Consider fusion partners (MBP, SUMO) to enhance solubility

  • Engineer codon optimization for the expression host

• Expression conditions:

  • Induce at lower temperatures (16-20°C) for longer periods

  • Test various induction methods (IPTG concentrations, auto-induction media)

  • Include membrane-stabilizing additives like glycerol (5-10%)

• Purification strategy:

  • Utilize gentle membrane solubilization with detergents (DDM, LMNG)

  • Employ multi-step purification (IMAC followed by size exclusion chromatography)

  • Include stabilizing agents throughout purification

The quality of purified protein should be assessed via activity assays specific to UbiB function and through biophysical characterization methods (circular dichroism, thermal shift assays) to ensure proper folding and stability.

What experimental approaches can determine if UbiB functions differently under aerobic versus anaerobic conditions in P. entomophila?

To investigate potential functional differences of UbiB under aerobic versus anaerobic conditions in P. entomophila, researchers should implement a multi-faceted experimental approach:

• Comparative expression analysis:

  • Quantify ubiB transcript levels using RT-qPCR under both conditions

  • Perform proteomic analysis to measure UbiB protein abundance

  • Use reporter gene fusions (luciferase, GFP) to monitor promoter activity in real-time

• Genetic manipulation and phenotypic assessment:

  • Generate ubiB deletion mutants and test growth under aerobic/anaerobic conditions

  • Create conditional expression strains using oxygen-responsive promoters

  • Perform complementation studies with ubiB variants

• Biochemical analysis:

  • Measure ubiquinone content using HPLC-MS under both conditions in wild-type and ubiB mutant strains

  • Quantify electron transport chain activity using oxygen consumption rates and membrane potential measurements

  • Assess interaction partners using co-immunoprecipitation or bacterial two-hybrid systems under different oxygen conditions

Given that research has identified an O2-independent pathway of ubiquinone biosynthesis that requires UbiB along with UbiU, UbiV, and UbiT , particular attention should be paid to measuring these interactions under varying oxygen concentrations, using techniques like bioluminescence resonance energy transfer (BRET) or fluorescence complementation assays.

What are the most reliable methods for evaluating UbiB expression levels in genetically modified P. entomophila strains?

For accurate quantification of UbiB expression in genetically modified P. entomophila strains, researchers should employ multiple complementary techniques:

• Transcriptional analysis:

  • RT-qPCR remains the gold standard for mRNA quantification, requiring careful primer design specific to P. entomophila ubiB and validated reference genes

  • RNA-seq provides broader context including potential effects on other metabolic pathways

• Protein-level quantification:

  • Western blotting with antibodies specific to UbiB or to an engineered epitope tag

  • Targeted proteomics approaches like Selected Reaction Monitoring (SRM) or Parallel Reaction Monitoring (PRM)

• Reporter systems:

  • Transcriptional fusions with fluorescent proteins allow real-time monitoring in living cells

  • Translational fusions can reveal protein localization patterns when subcellular fractionation is employed

When implementing recombineering approaches to modify ubiB, researchers should consider the potential for off-target mutations. Based on experience with P. putida, approximately 1.17 off-target mutations per recombineering cycle may occur , necessitating thorough genotypic verification of the generated strains through whole-genome sequencing.

How can researchers effectively measure the impact of UbiB mutations on ubiquinone biosynthesis in P. entomophila?

To effectively measure the impact of UbiB mutations on ubiquinone biosynthesis in P. entomophila, researchers should implement a comprehensive analytical approach:

• Direct measurement of ubiquinone content:

  • High-Performance Liquid Chromatography (HPLC) coupled with mass spectrometry (MS) for quantification of UQ levels and precursors

  • UV-visible spectroscopy for rapid screening of total quinone content

  • Isotope labeling experiments using 13C-labeled precursors to track biosynthetic flux

• Functional assessments:

  • Oxygen consumption rate measurements using respirometry

  • Membrane potential determination using fluorescent probes (e.g., DiSC3(5))

  • ATP production quantification under different respiratory conditions

• Phenotypic characterization:

  • Growth curve analysis under aerobic versus anaerobic conditions

  • Stress resistance profiling (oxidative, pH, antibiotic challenges)

  • Competitive fitness assays with wild-type strains

Given that UbiB functions in an oxygen-independent pathway of ubiquinone biosynthesis , particular attention should be paid to comparing phenotypes under varying oxygen conditions. The methodological approach should include creation of defined point mutations using single-stranded DNA recombineering techniques as established for Pseudomonas species, with efficiency enhancements like those described for the ReScribe system , which combines recombineering with CRISPR-Cas9 selection to achieve high editing efficiencies (>75%) in a time-efficient manner.

What are the most effective protocols for analyzing UbiB protein-protein interactions in the ubiquinone biosynthesis pathway?

For analyzing UbiB protein-protein interactions in the ubiquinone biosynthesis pathway, researchers should consider the following methodological approaches:

• In vivo interaction studies:

  • Bacterial two-hybrid (B2H) system optimized for Pseudomonas

  • Bimolecular Fluorescence Complementation (BiFC) to visualize interactions in their native cellular context

  • Förster Resonance Energy Transfer (FRET) using fluorescently tagged proteins

• Biochemical approaches:

  • Co-immunoprecipitation with antibodies against UbiB or interaction partners

  • Pull-down assays using affinity-tagged UbiB variants

  • Chemical crosslinking followed by mass spectrometry (XL-MS)

• Structural biology methods:

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

  • Cryo-electron microscopy of protein complexes

  • X-ray crystallography of co-purified complexes

When investigating the interactions between UbiB and other components of the O2-independent ubiquinone biosynthesis pathway, particular focus should be placed on UbiU, UbiV, and UbiT, which have been identified as key components of this pathway . For recombinant expression of these interacting partners, researchers should consider co-expression strategies to maintain complex integrity. The choice of detergents during membrane protein extraction is critical, as harsh detergents may disrupt physiologically relevant interactions. Mild detergents like DDM or nanodiscs can help preserve native membrane protein interactions.

How should researchers interpret UbiB function in the context of P. entomophila's adaptation to different environmental conditions?

When interpreting UbiB function in the context of P. entomophila's environmental adaptations, researchers should consider multiple layers of analysis:

• Comparative genomic analysis:

  • Examine conservation of ubiB across Pseudomonas species inhabiting different niches

  • Analyze regulatory elements controlling ubiB expression across species

  • Identify potential horizontal gene transfer events that may have shaped ubiB evolution

• Transcriptional response studies:

  • Evaluate ubiB expression under conditions mimicking P. entomophila's natural environment

  • Compare expression patterns with other respiratory chain components

  • Consider potential cross-regulation with stress response pathways

• Metabolic contextual analysis:

  • Assess ubiquinone metabolite profiles under different environmental conditions

  • Map metabolic flux through the ubiquinone pathway using labeled precursors

  • Consider interaction with other metabolic pathways (e.g., phosphate metabolism)

P. entomophila has specific adaptations for its lifestyle, including its ability to establish infections in laboratory strains of fruit flies, making it an ideal system for exploring host-pathogen biology . The unique regulatory architecture observed in P. entomophila, such as the placement of certain genes under the control of specific regulons like the Pho regulon , suggests that metabolic pathways including ubiquinone biosynthesis may be regulated differently compared to other Pseudomonas species. This unique configuration likely reflects the specific demands and opportunities of P. entomophila's habitat and lifestyle .

What are the key considerations when comparing UbiB function across different Pseudomonas species?

When comparing UbiB function across different Pseudomonas species, researchers should address several critical considerations:

• Sequence and structure analysis:

  • Perform comprehensive phylogenetic analysis of UbiB sequences

  • Identify conserved domains versus species-specific variations

  • Model structural differences that might impact function

• Regulatory context evaluation:

  • Compare promoter regions and transcription factor binding sites

  • Assess operon structures containing ubiB across species

  • Evaluate potential differential regulation in response to environmental cues

• Functional complementation experiments:

  • Test cross-species complementation using heterologous expression

  • Quantify restoration of phenotypes in ubiB mutants

  • Identify species-specific functional constraints

How can researchers differentiate between direct and indirect effects when studying UbiB mutations on bacterial physiology?

Differentiating between direct and indirect effects of UbiB mutations on bacterial physiology requires a systematic approach to data collection and analysis:

• Temporal analysis of effects:

  • Monitor immediate versus delayed consequences of conditional ubiB expression

  • Perform time-course metabolomics to identify primary versus secondary metabolic changes

  • Track transcriptional cascades following ubiB perturbation

• Genetic interaction mapping:

  • Construct double mutants (ubiB with interacting partners)

  • Perform synthetic genetic array analysis

  • Utilize CRISPRi for partial knockdowns of related pathways

• Rescue experiments:

  • Test chemical complementation with ubiquinone or pathway intermediates

  • Perform genetic complementation with wild-type versus mutant ubiB variants

  • Use metabolic bypasses to circumvent ubiquinone-dependent processes

• Systems biology approaches:

  • Integrate transcriptomic, proteomic, and metabolomic data sets

  • Apply network analysis to identify regulatory hubs affected by UbiB perturbation

  • Develop predictive models of metabolic flux

When implementing these approaches, researchers should be mindful of the potential for secondary mutations that can arise during genetic manipulation. For instance, research on P. putida demonstrated approximately 1.17 off-target mutations per recombineering cycle , which could confound interpretations of phenotypic effects if not accounted for through appropriate controls or whole-genome sequencing verification.

What emerging technologies could advance our understanding of UbiB function in P. entomophila?

Several cutting-edge technologies show promise for deepening our understanding of UbiB function in P. entomophila:

• CRISPR-Cas-based technologies:

  • CRISPRi/CRISPRa systems for tunable expression modulation

  • Base editing for precise nucleotide substitutions without double-strand breaks

  • Combinatorial CRISPR screens to identify genetic interactions

• Advanced imaging techniques:

  • Super-resolution microscopy for subcellular localization

  • Correlative light and electron microscopy to visualize UbiB in membrane contexts

  • FRET-based biosensors to monitor ubiquinone production in real-time

• Single-cell approaches:

  • Single-cell RNA-seq to capture heterogeneity in ubiB expression

  • Microfluidic devices for real-time monitoring of individual bacterial responses

  • Single-cell metabolomics to track ubiquinone pathway metabolites

The ReScribe system, which combines multiplex recombineering with CRISPR-Cas9 counterselection, represents a particularly promising technology for UbiB studies. This approach has demonstrated a 10-fold increase in efficiency and significant time reduction compared to standard recombineering methods . The ability to perform multiplex editing with efficiency levels of 77.8% in just 3 days could facilitate rapid generation of multiple UbiB variants for comparative functional studies.

How might understanding UbiB function contribute to engineering Pseudomonas species for biotechnological applications?

Understanding UbiB function in ubiquinone biosynthesis could significantly impact the engineering of Pseudomonas species for biotechnological applications in several ways:

• Metabolic engineering for bioproduction:

  • Optimization of electron transport chain efficiency for enhanced growth and productivity

  • Engineering redox balance for improved yields of valuable metabolites

  • Development of strains with customized respiratory profiles for specific fermentation conditions

• Bioremediation applications:

  • Enhancement of electron transport capacity for degradation of recalcitrant compounds

  • Improvement of survival under anaerobic conditions in contaminated environments

  • Creation of biosensors for monitoring environmental conditions

• Synthetic biology platforms:

  • Integration of UbiB and the anaerobic ubiquinone biosynthesis pathway into synthetic circuits

  • Development of genetic switches responsive to redox conditions

  • Creation of minimal Pseudomonas chassis with optimized respiratory capabilities

The methodological approach demonstrated in the creation of minimally recoded P. putida strains using ReScribe technology provides a valuable framework for such engineering efforts. This approach allowed researchers to recode 12 TAG codons in conditionally essential genes, reducing working time from 6 days per mutation with standard recombineering to just 3 days with single-targeting ReScribe, and achieving even greater efficiency with multiplex editing . Similar approaches could be applied to optimize UbiB and related genes for specific biotechnological applications.

What are the most promising approaches for studying the role of UbiB in P. entomophila pathogenicity?

To investigate the role of UbiB in P. entomophila pathogenicity, researchers should consider these methodological approaches:

• Infection model systems:

  • Utilize the established Drosophila infection model, which provides an ideal system for exploring host-pathogen biology

  • Develop cell culture models to examine specific aspects of pathogen-host cell interactions

  • Consider alternative models to test host range and infection dynamics

• Virulence factor analysis:

  • Generate precise ubiB mutations using ReScribe or similar recombineering systems

  • Perform comparative virulence assays between wild-type and ubiB mutant strains

  • Quantify production of known virulence factors under different respiratory conditions

• Host response studies:

  • Investigate insect physiological and immune responses to infection with ubiB variants

  • Examine the dynamics of antimicrobial peptide release in response to infection

  • Track host metabolic adaptations in response to altered bacterial respiration

• In vivo imaging approaches:

  • Develop fluorescent or bioluminescent reporters linked to ubiB expression

  • Track bacterial dissemination and growth dynamics during infection

  • Monitor respiratory activity during different infection phases

P. entomophila's ability to establish successful infections in laboratory strains of fruit flies makes it particularly valuable for exploring the connection between metabolism and pathogenicity . The ubiquinone biosynthesis pathway's role in maintaining cellular energy production could be crucial for sustaining infection and responding to host defense mechanisms, particularly under the varying oxygen concentrations encountered during the infection process.