Recombinant Shewanella oneidensis Probable ubiquinone biosynthesis protein UbiB (ubiB)

What is Shewanella oneidensis MR-1 and why is it significant for studying UbiB protein?

Shewanella oneidensis MR-1 is an aquatic, facultative anaerobic bacterium with extraordinary respiratory versatility, capable of utilizing a wide range of electron acceptors including oxygen, metals like Cr(VI), electrodes, and solvents such as dimethyl sulfoxide (DMSO). This respiratory diversity makes it an invaluable model organism for studying bioremediation of toxic and radioactive metals and for understanding extracellular electron transfer mechanisms . The bacterium shows great potential for environmental pollutant remediation and electrical current generation in applications like wastewater treatment .

Studying UbiB protein in S. oneidensis is particularly significant because of its probable role in ubiquinone biosynthesis. Ubiquinone (coenzyme Q) is a critical component of the electron transport chain that facilitates electron flow across the cellular membrane. Given S. oneidensis' diverse respiratory pathways and remarkable ability to transfer electrons to external acceptors, understanding UbiB's function provides crucial insights into how this bacterium maintains efficient energy metabolism under varying environmental conditions . The protein's role becomes even more significant considering that S. oneidensis forms nanowires (outer membrane extensions containing specialized cytochromes) under electron acceptor-limited conditions, a process that requires coordinated regulation of various electron transport components .

What is the structure and basic function of UbiB protein in Shewanella oneidensis?

The UbiB protein in Shewanella oneidensis is a full-length 549-amino acid protein encoded by the ubiB gene (locus SO_4201). Its amino acid sequence begins with MTLASIRRGYHVIKTLLQ and contains various functional domains typical of the UbiB protein family . The complete amino acid sequence reveals a complex protein structure that likely supports its enzymatic function in the ubiquinone biosynthetic pathway .

Functionally, UbiB is classified as a probable ubiquinone biosynthesis protein, suggesting its involvement in the production pathway of ubiquinone (coenzyme Q) . In bacteria, ubiquinone serves as an essential lipid-soluble electron carrier in the respiratory chain, facilitating electron transfer between various protein complexes. The protein is also described as a "probable protein kinase UbiB" in some annotations, indicating it likely functions as a kinase in the ubiquinone biosynthesis pathway . This enzymatic role would involve phosphorylation of substrate proteins or metabolic intermediates, a critical step in the complex multi-enzyme process of ubiquinone production. In S. oneidensis specifically, UbiB's function is particularly important given the organism's diverse respiratory capabilities and its need to maintain efficient electron transfer under varying environmental conditions .

How is recombinant UbiB protein typically expressed and purified for research purposes?

Recombinant Shewanella oneidensis UbiB protein is typically expressed using heterologous expression systems, with Escherichia coli being the preferred host organism. The gene encoding UbiB (ubiB) is cloned into an expression vector that incorporates an affinity tag, most commonly a His-tag (polyhistidine tag) at the N-terminus to facilitate purification . This expression strategy has been successfully implemented to produce functional UbiB protein for research applications.

For expression, the recombinant plasmid containing the ubiB gene is transformed into E. coli, and protein production is induced under controlled conditions . After sufficient growth and protein expression, cells are harvested and lysed to release the recombinant protein. The His-tagged UbiB protein is then purified from the cell lysate using immobilized metal affinity chromatography, typically with Ni-NTA resin that selectively binds to the His-tag . Following purification, the protein is often stored in a Tris/PBS-based buffer containing 6% trehalose at pH 8.0 to maintain stability .

How does UbiB function differ in aerobic versus anaerobic conditions in Shewanella oneidensis?

The function of UbiB protein in Shewanella oneidensis likely exhibits significant differences between aerobic and anaerobic conditions, reflecting the bacterium's remarkable respiratory versatility. Under aerobic conditions, UbiB primarily supports the canonical ubiquinone biosynthesis pathway essential for aerobic respiration, where oxygen serves as the terminal electron acceptor in the electron transport chain .

In contrast, under anaerobic conditions when S. oneidensis switches to alternative electron acceptors such as metals, electrodes, or solvents like DMSO, UbiB's role likely adapts to support these alternative respiratory pathways . RNA-Seq analysis of S. oneidensis under oxygen-limited conditions has revealed coordinated increased expression of heme biosynthesis, cytochrome maturation, and transport pathways, indicating that the bacterium increases cytochrome production during electron acceptor limitation . This includes upregulation of genes encoding specialized cytochromes like MtrA, MtrC, and OmcA that are essential for extracellular electron transfer .

While the search results don't provide direct evidence for changes in ubiB expression under different respiratory conditions, its function in ubiquinone biosynthesis would need to adapt to these changing respiratory requirements. The electron transport chain components, including ubiquinone, must accommodate electron flow to diverse acceptors under anaerobic conditions, suggesting that UbiB's activity might be integrated with the expression of specialized cytochromes involved in extracellular electron transfer . Interestingly, the expression of certain homologous genes (like mtrF and mtrD) remains unaffected or decreases under oxygen limitation, suggesting a functional specialization of different components of the electron transport machinery under various respiratory conditions .

What techniques are most effective for studying UbiB protein interactions with other components of the electron transport chain?

Studying UbiB protein interactions with other components of the electron transport chain in Shewanella oneidensis requires a multifaceted approach combining in vivo and in vitro techniques. Several methodologies have proven particularly effective for investigating membrane-associated proteins like UbiB in the context of S. oneidensis' unique respiratory capabilities.

Co-immunoprecipitation (Co-IP) coupled with mass spectrometry represents a powerful approach, using antibodies against tagged UbiB protein to pull down protein complexes, followed by mass spectrometric analysis to identify interacting partners . This technique can reveal both stable and transient interactions within the electron transport chain components. For more targeted studies, bacterial two-hybrid systems can screen for specific protein-protein interactions between UbiB and other electron transport chain components.

Biophysical techniques such as surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC) provide quantitative measurements of binding affinities and kinetics between purified UbiB and potential interaction partners. Cross-linking mass spectrometry can capture transient interactions and provide spatial information about protein complexes involving UbiB and other respiratory proteins.

For Shewanella-specific applications, researchers must consider the unique components of its electron transport chain, particularly those involved in extracellular electron transfer . Recent advances in genetic manipulation of S. oneidensis, including a new recombineering system that allows precise genome editing, enable the creation of tagged versions of UbiB and other proteins for interaction studies . Correlating interaction studies with functional assays under various respiratory conditions (aerobic vs. anaerobic with different electron acceptors) provides the most comprehensive understanding of UbiB's role in S. oneidensis' distinctive electron transport processes.

How can genetic engineering approaches be used to study UbiB function in Shewanella oneidensis?

Genetic engineering approaches for studying UbiB function in Shewanella oneidensis have been significantly enhanced by recent methodological advances. These sophisticated techniques allow researchers to precisely manipulate the ubiB gene and study its function in detail.

Prophage-mediated genome engineering (recombineering) represents a breakthrough technique for S. oneidensis, utilizing a λ Red Beta homolog from Shewanella sp. W3-18-1 . This system allows precise genome editing with single-strand DNA oligonucleotides, enabling the creation of markerless mutations with approximately 5% efficiency among total cells . Researchers can use this approach to introduce point mutations, small insertions, or deletions that target specific functional domains of UbiB without disrupting the entire gene, allowing for nuanced analysis of structure-function relationships.

A recently developed robust electroporation method for S. oneidensis achieves high efficiency (~4.0 x 10^6 transformants/μg DNA), facilitating the introduction of various genetic constructs . This technique maintains high transformation efficiency even when cells are frozen for long-term storage, providing practical advantages for laboratory work . The availability of synthetic plasmid toolkits specifically designed for S. oneidensis MR-1 further enhances the genetic manipulation capabilities, allowing for fine-tuned expression of ubiB using various promoters and replicons .

These genetic tools can be combined with phenotypic assays measuring ubiquinone levels, respiratory capabilities with various electron acceptors, and growth under different conditions to comprehensively characterize UbiB function in S. oneidensis. The ability to make precise, markerless mutations represents a significant advancement over previous methods that relied on transposon mutagenesis and targeted knockouts using suicide vectors for gene disruptions .

What are the optimal conditions for expressing functional recombinant UbiB protein?

The optimal conditions for expressing functional recombinant Shewanella oneidensis UbiB protein involve careful consideration of expression systems, growth parameters, and purification strategies. Based on available research data, the following conditions have been found to be effective:

Expression System Parameters:

Culture and Purification Conditions:

The expression and purification strategy typically yields recombinant UbiB protein with greater than 90% purity as determined by SDS-PAGE . The protein requires careful handling to maintain its structural integrity and functional activity, with particular attention to avoiding repeated freeze-thaw cycles that can compromise protein stability .

For functional validation, researchers should consider including activity assays specific to UbiB's role in ubiquinone biosynthesis, potentially including kinase activity measurements if appropriate. These optimized conditions ensure the production of high-quality recombinant UbiB protein suitable for various research applications, including structural studies, enzymatic assays, and interaction analyses.

How can researchers assess the enzymatic activity of UbiB in relation to ubiquinone biosynthesis?

Assessing the enzymatic activity of UbiB in relation to ubiquinone biosynthesis requires specialized approaches due to the complex nature of the ubiquinone pathway and UbiB's probable role as a protein kinase. Researchers can implement several complementary methods to evaluate UbiB's functionality in the context of S. oneidensis' unique respiratory capabilities.

In vitro kinase activity assays represent a direct approach to assess UbiB function, measuring its ability to transfer phosphate groups to potential substrates in the ubiquinone biosynthesis pathway. This typically involves incubating purified recombinant UbiB protein with candidate substrate proteins or metabolic intermediates in the presence of ATP, followed by detection of phosphorylation using various analytical techniques.

Complementation studies provide a powerful genetic approach to assess UbiB functionality. This involves expressing S. oneidensis UbiB in ubiB mutant strains and evaluating whether it restores ubiquinone production and respiratory functions. With the development of precise genetic engineering tools for S. oneidensis, including prophage-mediated genome engineering and efficient electroporation methods , researchers can create clean ubiB knockout strains for such studies.

Ubiquinone quantification provides direct evidence of UbiB's role in the biosynthetic pathway. Techniques such as High-Performance Liquid Chromatography (HPLC) with electrochemical detection or Liquid Chromatography with tandem Mass Spectrometry (LC-MS/MS) can precisely measure ubiquinone levels in wild-type versus UbiB-modified strains. Extraction protocols typically involve lipid extraction using organic solvents, followed by separation and detection of ubiquinone and its precursors.

When designing these assays, researchers should consider S. oneidensis' respiratory versatility and adapt methods to account for potential differences in ubiquinone utilization under various electron acceptor conditions, particularly given the bacterium's ability to use metals, electrodes, and organic compounds as terminal electron acceptors .

What bioinformatic approaches are most useful for analyzing UbiB protein function and evolutionary relationships?

Bioinformatic approaches for analyzing UbiB protein function and evolutionary relationships in Shewanella oneidensis require a comprehensive toolset that integrates sequence, structural, and comparative genomic analyses. These computational methods provide valuable insights into UbiB's role in S. oneidensis' unique respiratory capabilities.

Multiple sequence alignment (MSA) represents a fundamental approach for identifying conserved domains and motifs across UbiB homologs from different bacterial species. Analysis of the 549-amino acid sequence of S. oneidensis UbiB reveals conservation patterns that can highlight functionally important residues. Profile hidden Markov models (HMMs) can further detect distant homology relationships, particularly useful given UbiB's classification as a "probable ubiquinone biosynthesis protein" .

Structural bioinformatics approaches are particularly valuable for understanding UbiB function. Homology modeling can predict UbiB's 3D structure based on related proteins, while molecular dynamics simulations can study protein flexibility and potential binding sites. These approaches are especially relevant given UbiB's probable role as a protein kinase in the ubiquinone biosynthesis pathway .

Comparative genomics provides a broader evolutionary context for understanding UbiB function. Synteny analysis examining the genomic context of ubiB (SO_4201) across Shewanella species and related genera can reveal co-evolutionary patterns with other components of the respiratory machinery. This is particularly relevant given S. oneidensis' ability to modulate expression of various respiratory components under different conditions, as demonstrated by RNA-Seq analysis showing coordinated expression of electron transport chain components under oxygen limitation .

Phylogenetic analysis using maximum likelihood or Bayesian inference methods can elucidate the evolutionary history of UbiB and its relationship to homologs in other bacteria. This approach can identify potential specialization of UbiB function in S. oneidensis related to its unique respiratory capabilities, particularly its ability to perform extracellular electron transfer .

What are the major challenges in studying UbiB function in Shewanella oneidensis and how can they be addressed?

The study of UbiB function in Shewanella oneidensis presents several significant challenges, each requiring specific methodological approaches to overcome. These challenges and their solutions represent important considerations for researchers investigating this protein's role in S. oneidensis' unique respiratory capabilities.

Table 1: Challenges and Solutions in Studying UbiB in S. oneidensis

Until recently, genetic manipulation of S. oneidensis was challenging due to limited genetic tools, with bacterial conjugation being the only reliable method for introducing DNA at high efficiency . The development of new techniques including prophage-mediated genome engineering and a robust electroporation method has significantly advanced the field, enabling markerless mutations and more sophisticated genetic studies of ubiB . These techniques achieve approximately 5% recombinants among total cells, representing a major improvement over previous methods .

Expression and purification of membrane-associated proteins like UbiB presents another significant challenge. Optimized protocols using E. coli expression systems with His-tagged constructs have been developed, with specific storage conditions (Tris/PBS-based buffer with 6% trehalose at pH 8.0) helping maintain protein stability . Avoiding repeated freeze-thaw cycles is crucial for maintaining protein function .

By addressing these challenges through integrated experimental approaches, researchers can develop a more comprehensive understanding of UbiB's role in S. oneidensis' remarkable respiratory versatility, particularly its ability to perform extracellular electron transfer under various environmental conditions.

How does UbiB protein contribute to Shewanella oneidensis' ability to perform extracellular electron transfer?

The contribution of UbiB protein to Shewanella oneidensis' extracellular electron transfer (EET) capabilities involves several interconnected mechanisms, though the relationship is complex and partially indirect. Understanding this connection requires examining UbiB's role in the context of S. oneidensis' unique respiratory adaptability.

As a probable ubiquinone biosynthesis protein , UbiB likely plays a critical role in maintaining adequate levels of ubiquinone, an essential lipid-soluble electron carrier in the respiratory chain. Ubiquinone serves as a central electron carrier in the inner membrane electron transport chain, facilitating electron flow from various dehydrogenases to terminal reductases. This establishes the electrochemical potential necessary for driving electrons through the Mtr pathway (involving MtrA, MtrB, and MtrC proteins) that ultimately enables extracellular electron transfer.

Research on S. oneidensis under electron acceptor limitation has shown coordinated expression of various respiratory components, including increased expression of heme biosynthesis pathways and cytochromes like MtrC and OmcA, which are essential for extracellular electron transfer . While specific data on UbiB expression under these conditions isn't directly provided in the search results, its role in ubiquinone biosynthesis suggests coordination with these pathways to maintain efficient electron flux.

S. oneidensis forms nanowires (extensions of its outer membrane containing cytochromes MtrC and OmcA) under oxygen-limited conditions . The ubiquinone pool, which UbiB helps maintain through its biosynthetic function, likely serves as an important electron reservoir during transitions between different respiratory modes, facilitating rapid adaptation to changing electron acceptor availability. Additionally, efficient extracellular electron transfer requires proper energy conservation mechanisms, where ubiquinone participates in proton-motive force generation essential for ATP synthesis.

Understanding UbiB's contribution to extracellular electron transfer has been facilitated by recent advances in genetic manipulation tools for S. oneidensis , allowing more precise investigation of the relationship between ubiquinone biosynthesis and the unique respiratory capabilities of this environmentally important bacterium.

What recent technological advances have improved our ability to study UbiB and similar proteins in Shewanella oneidensis?

Recent technological advances have significantly enhanced our ability to study UbiB and similar proteins in Shewanella oneidensis, spanning genetic manipulation, expression systems, and functional characterization methodologies. These advances have transformed researchers' capabilities to investigate the complex respiratory mechanisms of this environmentally important bacterium.

Advanced genetic engineering tools represent a major breakthrough in S. oneidensis research. A prophage-mediated genome engineering (recombineering) system using a λ Red Beta homolog from Shewanella sp. W3-18-1 enables precise genome editing with single-strand DNA oligonucleotides, achieving approximately 5% recombinants among total cells . This represents the first effective and simple strategy for recombination with markerless mutations in S. oneidensis . Additionally, a robust electroporation method achieving efficiency of ~4.0 x 10^6 transformants/μg DNA has overcome previous limitations in transformation efficiency .

The development of synthetic plasmid toolkits specifically designed for S. oneidensis MR-1 provides versatile options for gene expression studies . Previously, genetic manipulation was challenging due to limited genetic tools, with bacterial conjugation being the only reliable method for introducing DNA at high efficiency . These advances now allow researchers to precisely manipulate genes like ubiB to study their function in detail.

High-throughput transcriptomic approaches, particularly RNA-Seq analysis techniques, have been successfully applied to S. oneidensis to determine differential gene expression under varying conditions, such as oxygen limitation . These approaches allow researchers to place UbiB function in the context of broader cellular responses and identify co-regulated genes, particularly important given S. oneidensis' ability to form nanowires and increase cytochrome production during electron acceptor limitation .

Production of recombinant proteins from S. oneidensis has also advanced, with established protocols for expressing and purifying proteins like UbiB with high purity (>90%) using His-tagging and appropriate storage conditions (Tris/PBS-based buffer with 6% trehalose at pH 8.0) . These technological advances collectively enable more comprehensive characterization of UbiB's structure, function, and physiological context, advancing our understanding of its role in S. oneidensis' remarkable respiratory versatility.

How does UbiB protein structure and function compare between Shewanella oneidensis and other bacteria?

The UbiB protein structure and function show both conservation and divergence between Shewanella oneidensis and other bacteria, reflecting evolutionary adaptations to different ecological niches and respiratory strategies. This comparative understanding provides valuable insights into the specialized role of UbiB in S. oneidensis' unique respiratory capabilities.

This functional diversity may be reflected in regulatory differences, with S. oneidensis potentially showing different expression patterns of ubiB under various respiratory conditions compared to bacteria with more limited respiratory options. RNA-Seq analysis has revealed that S. oneidensis undergoes significant transcriptional reprogramming under oxygen-limited conditions, with coordinated increased expression of heme biosynthesis, cytochrome maturation, and transport pathways . While specific data on ubiB regulation is not provided in the search results, its function suggests integration with these respiratory adaptation mechanisms.

Understanding these comparative aspects of UbiB structure and function contributes to our knowledge of how S. oneidensis has evolved its remarkable ability to utilize diverse electron acceptors, a capability with significant implications for bioremediation and bioelectrochemical applications.

How is UbiB expression regulated in response to different environmental conditions in Shewanella oneidensis?

The regulation of UbiB expression in response to environmental conditions in Shewanella oneidensis involves complex mechanisms that allow the bacterium to adapt its respiratory capabilities to varying electron acceptor availability and redox conditions. While the search results don't provide direct data on ubiB regulation specifically, insights can be drawn from what is known about S. oneidensis' transcriptional responses to changing environments.

S. oneidensis undergoes significant transcriptional reprogramming under oxygen-limited conditions, as revealed by RNA-Seq analysis . Under these conditions, the bacterium increases expression of heme biosynthesis, cytochrome maturation, and transport pathways, including genes encoding MtrA, MtrC, and OmcA, which are essential for extracellular electron transfer . Given UbiB's role in ubiquinone biosynthesis, which is essential for both aerobic and anaerobic respiration in S. oneidensis, its expression is likely coordinated with these respiratory pathways.

Interestingly, not all respiratory components show the same expression patterns under oxygen limitation. The expression of mtrF and mtrD (homologs of mtrA and mtrC) either remains unaffected or decreases under these conditions , suggesting a functional specialization of different components of the electron transport machinery. This differential regulation indicates that S. oneidensis has evolved sophisticated regulatory mechanisms to optimize its respiratory apparatus for specific environmental conditions.

The development of new genetic tools for S. oneidensis, including prophage-mediated genome engineering and efficient electroporation methods , provides opportunities for more detailed investigation of ubiB regulation. These tools enable the construction of reporter gene fusions to study ubiB promoter activity under different growth conditions and the creation of precisely engineered mutants to investigate regulatory mechanisms.

Understanding UbiB regulation in the context of S. oneidensis' respiratory versatility has implications beyond basic science, as this bacterium's ability to adapt to diverse electron acceptors underlies its potential applications in bioremediation of toxic and radioactive metals and in bioelectrochemical systems .

What role does UbiB play in Shewanella oneidensis' stress response mechanisms?

The role of UbiB in Shewanella oneidensis' stress response mechanisms is multifaceted, involving both direct and indirect contributions to cellular resilience under various stress conditions. While the search results don't provide direct evidence for UbiB's role in stress response, its function in ubiquinone biosynthesis suggests significant involvement in maintaining cellular homeostasis during stress.

Ubiquinone, whose biosynthesis likely involves UbiB, acts as an antioxidant in bacterial membranes, scavenging reactive oxygen species and helping maintain redox homeostasis. This antioxidant function becomes particularly important during oxidative stress, which S. oneidensis may encounter in its natural environments or during transitions between aerobic and anaerobic respiration. Interestingly, S. oneidensis contains proteins like SYE4 (a member of the Old Yellow Enzyme family) that are induced under oxidative stress conditions for protection against oxidative damage . UbiB likely complements these dedicated oxidative stress response proteins by ensuring sufficient ubiquinone production during oxidative challenge.

During electron acceptor limitation, S. oneidensis undergoes significant transcriptional reprogramming, forms nanowires, and increases expression of cytochromes involved in extracellular electron transfer . UbiB's role in ubiquinone biosynthesis would be crucial during these transitions to maintain efficient electron flow through alternative respiratory pathways, alleviating stress caused by electron acceptor limitation.

S. oneidensis is known for its ability to reduce toxic metals, a process that can also protect the cell from metal toxicity. The efficient reduction of metals requires functional electron transport chains, in which ubiquinone plays a central role. UbiB likely contributes to metal stress tolerance by supporting the respiratory pathways involved in detoxification processes.

The recent development of advanced genetic tools for S. oneidensis, including precise genome editing techniques and high-efficiency transformation methods , opens new avenues for investigating UbiB's specific roles in stress response mechanisms. These tools enable the creation of defined ubiB mutants and the precise regulation of ubiB expression to determine its contribution to stress tolerance under various environmental conditions.