Recombinant Citrobacter koseri 4-hydroxybenzoate octaprenyltransferase (ubiA)

What is Citrobacter koseri 4-hydroxybenzoate octaprenyltransferase (ubiA)?

Citrobacter koseri 4-hydroxybenzoate octaprenyltransferase (ubiA) is a bacterial enzyme encoded by the ubiA gene (also known as Ordered Locus Name CKO_03875) in Citrobacter koseri. According to product specifications, it is a full-length protein consisting of 289 amino acids with an EC classification of 2.5.1.-. The enzyme is also known as 4-HB polyprenyltransferase . It functions in the biosynthetic pathway of ubiquinone (coenzyme Q), which is essential for cellular respiration and energy production in bacteria.

The complete amino acid sequence of this protein is:
MEWSLTQNKLLAFHRLMRTDKPIGALLLLWPTLWALWVATPGVPQLWILAVFVAGVWLMRAAGCVVNDYADRKFDGHVKRTANRPLPSGAVTEKEARTLFVVLVALSFLLVLTLNTMTILLSIAALALAWVYPFMKRYTHLPQVVLGAAFGWSIPMAFAAVSESVPLSCWLMFLANILWAVAYDTQYAMVDRDDDLKIGIKSTAILFGRHDKLIIGILQIAVLALMALIGWLNGLGWYYWSVLVAGALFVYQQKLIVGREREACFKAFMNNNYVGLVLFLGLAMSYVG

How does ubiA function in bacterial metabolism?

The 4-hydroxybenzoate octaprenyltransferase (ubiA) enzyme catalyzes a key step in ubiquinone biosynthesis by transferring a prenyl group to 4-hydroxybenzoate. This reaction is essential for the electron transport chain and cellular respiration.

Methodologically, researchers investigating ubiA function typically:

• Perform enzymatic assays using purified recombinant protein

• Conduct complementation studies in ubiA-deficient bacterial strains

• Measure ubiquinone levels in wildtype versus ubiA-knockout strains

• Analyze growth patterns in minimal media where electron transport chain function is critical

While the search results don't specifically detail the metabolic role of ubiA in C. koseri, comparative genomic analyses suggest that core metabolic functions like ubiquinone biosynthesis are generally conserved across Citrobacter species .

What are the optimal storage conditions for recombinant Citrobacter koseri ubiA protein?

Based on product specifications, recombinant Citrobacter koseri 4-hydroxybenzoate octaprenyltransferase (ubiA) should be stored at -20°C for regular usage, and at -80°C for extended storage periods. The protein is typically supplied in a Tris-based buffer containing 50% glycerol that has been optimized for protein stability .

To maintain protein activity, researchers should:

• Aliquot the protein upon first thawing to avoid repeated freeze-thaw cycles

• Store working aliquots at 4°C for up to one week

• Avoid repeated freezing and thawing which can lead to protein denaturation and loss of enzymatic activity

When designing experiments, it's important to consider the stability profile of the protein. Activity assays should ideally be performed with freshly thawed protein or within the recommended storage period at 4°C.

What role does ubiA play in Citrobacter koseri virulence and pathogenicity?

While the specific contribution of ubiA to C. koseri virulence isn't directly addressed in the search results, we can analyze its potential role through metabolic and virulence pathways.

C. koseri is known for its tropism for the brain parenchyma, causing aggressive neonatal meningitis that can progress to brain abscesses . Comparative genomic analyses have identified several virulence factors in C. koseri, including genes associated with:

• Flagellar apparatus biosynthesis (ompA, csg fimbriae, che operon)

• Iron uptake systems (chu, fep, and ent genes)

• High pathogenicity island (HPI) cluster

As a metabolic enzyme, ubiA may contribute to virulence indirectly by:

• Ensuring energy production required for bacterial survival in host environments

• Contributing to membrane stability and composition

• Potentially playing a role in oxidative stress resistance

An experimental approach to assess ubiA's role in virulence would involve:

• Creating ubiA knockout mutants in C. koseri

• Comparing growth and survival in macrophage infection models

• Assessing invasion and intracellular survival rates

• Determining virulence in animal models similar to those used for HPI mutant studies

Notably, C. koseri has been demonstrated to survive intracellularly in both primary microglia and macrophages, suggesting these cells may serve as reservoirs for pathogen persistence during CNS infections . Whether ubiA contributes to this ability would be an interesting research question.

How can recombinant Citrobacter koseri ubiA be utilized as a potential drug target?

The potential of Citrobacter koseri proteins as drug targets has gained significance due to increasing antibiotic resistance. Recent research employing subtractive proteomics has identified promising vaccine targets against C. koseri, though ubiA specifically was not mentioned among the top candidates .

To evaluate ubiA as a potential drug target, researchers could:

• Conduct structural analysis:

  • Resolve the protein structure through X-ray crystallography or cryo-EM

  • Identify active site residues and substrate binding pockets

  • Perform molecular docking studies to screen potential inhibitors

• Validate essentiality:

  • Create conditional ubiA mutants to confirm its requirement for growth

  • Assess bacterial survival under various environmental conditions when ubiA is inhibited

  • Determine if alternative metabolic pathways can compensate for ubiA inhibition

• Develop screening assays:

  • Establish high-throughput enzymatic assays to screen compound libraries

  • Measure enzyme kinetics in the presence of potential inhibitors

  • Develop whole-cell assays to validate hits from enzymatic screens

• In silico approach:
  Similar to the approach used for other C. koseri proteins , researchers could:

  • Perform comparative genomics to ensure targeting specificity

  • Identify epitopes for potential vaccine development

  • Use molecular dynamics simulations to study protein-inhibitor interactions

The successful development of a vaccine candidate against C. koseri using bioinformatics and immunoinformatics approaches suggests that similar methodologies could be applied to evaluate ubiA as either a drug target or vaccine component.

What experimental approaches can be used to study ubiA enzyme kinetics and substrate specificity?

Studying the enzyme kinetics and substrate specificity of 4-hydroxybenzoate octaprenyltransferase (ubiA) requires a combination of biochemical, biophysical, and computational approaches:

• Purification optimization for active enzyme:

  • Express protein with various tags (His, GST, MBP) to identify optimal solubility

  • Test different expression systems (E. coli, yeast, insect cells)

  • Optimize buffer conditions to maintain membrane protein activity

  • Consider detergent screening for this membrane-associated enzyme

• Enzyme activity assays:

  • Radiometric assays using 14C-labeled substrates

  • HPLC-based assays to detect product formation

  • Coupled enzyme assays that link ubiA activity to measurable outputs

  • Fluorescence-based assays for high-throughput screening

• Substrate specificity determination:

  • Test various prenyl donors (different chain lengths)

  • Examine alternative aromatic acceptors beyond 4-hydroxybenzoate

  • Create a substrate competition matrix to determine preference

  • Analyze reaction products by mass spectrometry

• Mutagenesis studies:

  • Identify conserved residues through sequence alignment

  • Create point mutations of catalytic site residues

  • Analyze the effect of mutations on enzyme kinetics parameters (Km, Vmax)

  • Perform complementation studies in ubiA-deficient strains

When designing such experiments, researchers should consider the transmembrane nature of ubiA, which presents challenges for traditional enzyme assays and may require specialized techniques for membrane protein analysis.

How does Citrobacter koseri ubiA compare to homologous proteins in other bacterial species?

Comparative analysis of Citrobacter koseri ubiA with homologs in other bacterial species provides insights into evolutionary conservation and potential functional differences:

The ubiA protein belongs to a family of prenyltransferases found across many bacterial species. While specific comparative data for C. koseri ubiA isn't provided in the search results, general principles for such analysis would include:

• Sequence alignment and phylogenetic analysis:

  • Multiple sequence alignment with ubiA homologs from other Enterobacteriaceae

  • Phylogenetic tree construction to determine evolutionary relationships

  • Identification of conserved domains and species-specific variations

• Structural comparison:

  • Homology modeling based on crystallized ubiA proteins from other species

  • Comparison of active site architecture across species

  • Analysis of species-specific structural elements

• Functional complementation:

  • Cross-species complementation studies using ubiA from different bacteria

  • Determination if C. koseri ubiA can restore function in ubiA mutants of other species

  • Evaluation of substrate specificity differences between homologs

The comparative genomic analysis approach used for other Citrobacter virulence factors could be applied specifically to ubiA to identify unique features of the C. koseri enzyme that might contribute to its pathogenicity or metabolism.

What is the relationship between ubiA activity and bacterial response to oxidative stress?

The relationship between 4-hydroxybenzoate octaprenyltransferase (ubiA) activity and bacterial response to oxidative stress represents an important area of investigation, particularly in the context of host-pathogen interactions:

• Mechanistic relationship:

  • Ubiquinone, synthesized through the ubiA pathway, serves as an electron carrier in respiratory chains

  • Beyond its role in energy production, ubiquinone functions as a membrane-bound antioxidant

  • Ubiquinone can directly scavenge reactive oxygen species (ROS)

  • Impaired ubiquinone synthesis may lead to increased susceptibility to oxidative damage

• Experimental approaches to investigate this relationship:

  • Create ubiA conditional mutants and expose to various oxidative stressors (H₂O₂, paraquat)

  • Measure ROS production in wildtype versus ubiA-deficient strains

  • Analyze expression of oxidative stress response genes in ubiA mutants

  • Determine survival rates under oxidative conditions with and without ubiquinone supplementation

• Relevance to host-pathogen interactions:

  • During infection, C. koseri faces oxidative burst from host immune cells, particularly macrophages and microglia

  • The ability to survive intracellularly in microglia may depend partly on resistance to oxidative damage

  • Modulation of ubiA expression or activity could potentially be a bacterial adaptation to host-derived oxidative stress

This relationship is particularly relevant considering that C. koseri has been shown to survive within macrophages and microglia , cells that typically generate ROS as antimicrobial defense mechanisms.

What are the optimal conditions for expressing and purifying recombinant Citrobacter koseri ubiA?

Expressing and purifying membrane-associated proteins like 4-hydroxybenzoate octaprenyltransferase (ubiA) presents specific challenges that require optimization:

• Expression systems:

  • E. coli (strain-K12) with pET-28a(+) vector has been successfully used for C. koseri proteins

  • Consider specialized E. coli strains designed for membrane protein expression (C41, C43)

  • Alternative systems: Pichia pastoris for eukaryotic-like folding or insect cell systems for complex proteins

• Expression conditions optimization:

  • Temperature: Lower temperatures (16-20°C) often improve membrane protein folding

  • Induction: Use lower IPTG concentrations (0.1-0.5 mM) for slower, more controlled expression

  • Media supplementation: Addition of glycerol or specific lipids may improve stability

  • Duration: Extended expression times at lower temperatures may yield better results

• Purification strategy:

  Step	Method	Buffer Components	Critical Considerations
  Cell lysis	Mechanical disruption	Tris pH 8.0, 150 mM NaCl, protease inhibitors	Gentle lysis to preserve membrane integrity
  Membrane extraction	Detergent solubilization	Mild detergents (DDM, LMNG)	Screen multiple detergents for optimal activity retention
  Affinity chromatography	Ni-NTA for His-tagged protein	Imidazole gradient, detergent above CMC	Low imidazole in wash buffers to reduce non-specific binding
  Size exclusion	Superdex 200	Tris buffer with detergent	Assess oligomeric state and homogeneity
  Storage	Flash freezing	50% glycerol, as used for commercial preparation	Aliquot to avoid freeze-thaw cycles

• Quality control assessment:

  • SDS-PAGE for purity evaluation

  • Western blot for identity confirmation

  • Mass spectrometry for accurate mass determination

  • Circular dichroism to verify secondary structure

  • Activity assays to confirm functional state

The commercial preparation of recombinant C. koseri ubiA is stored in Tris-based buffer with 50% glycerol , suggesting this formulation maintains stability, which could be used as a starting point for lab-scale preparations.

How can researchers develop assays to screen for inhibitors of Citrobacter koseri ubiA?

Developing robust assays for screening inhibitors of 4-hydroxybenzoate octaprenyltransferase (ubiA) requires consideration of the enzyme's membrane association and biochemical properties:

• Primary enzymatic assays:

  • Radiometric assay: Monitor the transfer of 14C-labeled prenyl group to 4-hydroxybenzoate

  • HPLC-based assay: Detect formation of prenylated product

  • Fluorescence proximity assay: Design fluorescent substrate analogs that change properties upon prenylation

  • Coupled enzyme assay: Link ubiA activity to a readily detectable enzymatic reaction

• High-throughput screening adaptations:

  Assay Format	Readout	Advantages	Limitations
  Fluorescence polarization	Change in polarization upon substrate binding	No separation steps required	May have high background
  FRET-based assay	Energy transfer upon product formation	Real-time monitoring possible	Requires labeled substrates
  SPA (Scintillation Proximity Assay)	Radioactive signal	High sensitivity	Requires radioactive materials
  Thermal shift assay	Protein stability changes upon inhibitor binding	Simple to implement	Indirect measure of inhibition

• Secondary assays for hit validation:

  • Dose-response curves to determine IC50 values

  • Mechanism of action studies (competitive vs. non-competitive)

  • Counter-screening against human homologs for selectivity

  • Whole-cell assays to confirm cellular activity

• In silico screening approaches:
  Similar to methods used for other C. koseri targets :

  • Structure-based virtual screening against ubiA homology models

  • Molecular dynamics simulations to identify stable binding modes

  • MMGBSA calculations to estimate binding energies

  • Machine learning models to predict activity from structural features

The approach used for identifying vaccine candidates against C. koseri through computational methods demonstrates the feasibility of in silico approaches that could be adapted for small molecule inhibitor discovery targeting ubiA.

What techniques can be used to study the role of ubiA in Citrobacter koseri infection models?

Investigating the role of 4-hydroxybenzoate octaprenyltransferase (ubiA) in Citrobacter koseri infection requires multiple experimental approaches spanning from molecular biology to animal models:

• Genetic manipulation strategies:

  • Generation of ubiA deletion mutants using CRISPR-Cas9 or homologous recombination

  • Construction of conditional mutants for essential genes

  • Complementation studies to confirm phenotype specificity

  • Reporter fusion constructs to monitor ubiA expression during infection

• In vitro infection models:

  • Macrophage infection model: C. koseri can survive intracellularly in macrophages

  • Microglial cell infection: Relevant for CNS tropism of C. koseri

  • Human brain microvascular endothelial cell (HBMEC) model: To study blood-brain barrier penetration

  • Organoid models: To mimic complex tissue environments

• Animal infection models:
  Similar to those used for studying HPI mutants :

  • 2-day-old SD rat model for neonatal meningitis

  • 18-day-old BALB/c mice for CNS infection

  • Monitoring parameters:

    • Bacterial load in blood and cerebrospinal fluid (CSF)

    • Inflammatory markers and cytokine profiles

    • Tissue histopathology

    • Survival rates and clinical scores

• Analysis of host-pathogen interactions:

  • Transcriptomics to identify host genes affected by ubiA activity

  • Metabolomics to detect ubiquinone-related metabolites during infection

  • Imaging techniques to track bacterial dissemination

  • Immunological assays to measure TLR4-dependent responses potentially affected by ubiA activity

The experimental approaches used to study the role of the High Pathogenicity Island (HPI) in C. koseri and the investigation of TLR4-mediated microglial responses to C. koseri provide valuable methodological frameworks that could be adapted for studying ubiA's role in pathogenesis.

What are the most promising future research directions for Citrobacter koseri ubiA studies?

Based on the current knowledge and gaps identified, several high-priority research directions emerge for Citrobacter koseri 4-hydroxybenzoate octaprenyltransferase (ubiA):

• Structural biology studies:

  • Determination of high-resolution crystal or cryo-EM structure

  • Characterization of substrate binding sites and catalytic mechanism

  • Structural comparison with homologs from other bacterial species and human counterparts

• Role in pathogenesis:

  • Investigation of ubiA contribution to C. koseri survival within microglia and macrophages

  • Analysis of ubiA expression during different stages of infection

  • Determination if ubiA influences TLR4-mediated immune responses

• Therapeutic targeting:

  • Development of selective inhibitors using structure-based drug design

  • Exploration of ubiA as a potential vaccine component, similar to approaches used for other C. koseri proteins

  • Investigation of synergistic effects between ubiA inhibitors and current antibiotics

• Fundamental biochemistry:

  • Detailed enzyme kinetics and substrate specificity studies

  • Investigation of potential regulatory mechanisms controlling ubiA activity

  • Exploration of ubiquinone biosynthesis pathway interactions with other cellular processes

• Methodological advances:

  • Development of improved expression and purification protocols for obtaining large quantities of active enzyme

  • Creation of high-throughput screening assays for inhibitor discovery

  • Establishment of genetic tools specifically for manipulating C. koseri genes