Recombinant Yersinia pseudotuberculosis serotype IB Probable 4-amino-4-deoxy-L-arabinose-phosphoundecaprenol flippase subunit ArnE (arnE)
Description
Yersinia pseudotuberculosis: Taxonomic Classification and Pathogenesis
Yersinia pseudotuberculosis is a Gram-negative bacterium belonging to the Yersiniaceae family within the order Enterobacterales. This pathogen is classified within the domain Bacteria, kingdom Pseudomonadati, and phylum Pseudomonadota . As a member of the Gammaproteobacteria class, Y. pseudotuberculosis shares genetic similarities with other significant pathogens in the Yersinia genus, including Y. enterocolitica and Y. pestis, the causative agent of plague .
Y. pseudotuberculosis causes Far East scarlet-like fever in humans, who are typically infected through zoonotic transmission, predominantly via the food-borne route . The bacterium is characterized by its urease-positive nature and ability to cause tuberculosis-like symptoms in animals, including localized tissue necrosis and granulomas in the spleen, liver, and lymph nodes . Human infections manifest with fever and right-sided abdominal pain, often mimicking appendicitis, especially in children and younger adults . In some cases, the infection can lead to skin complaints (erythema nodosum), joint stiffness and pain (reactive arthritis), or bacteremia .
Virulence Mechanisms of Yersinia Species
The pathogenicity of Yersinia species, including Y. pseudotuberculosis, is largely dependent on a 70-kb virulence plasmid that encodes a complex type III secretion system (Ysc) and Yersinia outer proteins (Yop) . After binding to host cells, Yersinia delivers Yop effector proteins directly into the host cell cytoplasm through this specialized secretion mechanism . These effector proteins interfere with host cell signaling pathways to subvert immune responses and facilitate bacterial survival within the host.
Among these virulence factors, YopT has been shown to cause disruption of the actin cytoskeleton in host cells by inhibiting the interaction between RhoA and its effectors . This mechanism illustrates how Yersinia species manipulate host cellular processes to enhance their pathogenicity.
Function and Components of the Arn Operon
The arn operon (also known as pmr operon in some species) is essential for the covalent modification of lipid A with 4-amino-4-deoxy-L-arabinose (Ara4N), a critical mechanism for antimicrobial resistance in many Gram-negative bacteria . The operon consists of several genes, including arnA, arnB, arnC, arnD, arnE, arnF, and arnT, each encoding proteins with specific functions in the Ara4N modification pathway.
The general pathway involves the synthesis of UDP-Ara4N from UDP-glucose, followed by its transfer to the lipid carrier undecaprenyl phosphate (BP), deformylation, and finally, transfer to lipid A . This modification reduces the negative charge of the bacterial outer membrane, decreasing the binding affinity of cationic antimicrobial peptides and thus conferring resistance.
Role of 4-amino-4-deoxy-L-arabinose in Bacterial Resistance
Research has demonstrated that lipopolysaccharides (LPS) of polymyxin B-resistant mutants of Escherichia coli contain 4-amino-4-deoxy-L-arabinopyranose (L-Arap4N), which is not normally a component of E. coli LPS . The presence of this aminopentose, linked to lipid A, correlates with resistance to cationic antimicrobial peptides like polymyxin B. This modification reduces the negative charge of the bacterial outer membrane, decreasing the electrostatic interaction with positively charged antimicrobial peptides .
Studies have shown that mutations in the arn operon genes disrupt this modification pathway and restore susceptibility to antimicrobial peptides. For instance, ΔarnC mutations in E. coli prevent the formation of BP-Ara4N, while ΔarnD mutations lead to the accumulation of BP-Ara4FN (the formylated precursor of BP-Ara4N) .
The Role of Flippase Subunits in Cellular Processes
Flippase proteins are essential membrane transporters that facilitate the movement of lipid molecules between the inner and outer leaflets of biological membranes. In the context of the Arn pathway, the ArnE protein functions as a subunit of the 4-amino-4-deoxy-L-arabinose-phosphoundecaprenol flippase complex.
The flippase complex, composed of ArnE and ArnF subunits, is responsible for translocating undecaprenyl phosphate-linked Ara4N (BP-Ara4N) from the cytoplasmic face to the periplasmic face of the inner membrane. This translocation is a critical step in the process of lipid A modification, as it positions the Ara4N donor in the periplasm where it can be transferred to lipid A by the ArnT transferase.
Methods for Recombinant Protein Production
Recombinant protein technology allows for the isolation and production of specific proteins outside their native organisms. For the production of recombinant Y. pseudotuberculosis ArnE, molecular cloning techniques would typically involve isolating the arnE gene, inserting it into an expression vector, and introducing this construct into a suitable host organism, often E. coli.
Similar approaches have been used with other Yersinia proteins, such as YopT, which was cloned and expressed as a glutathione S-transferase fusion protein for functional studies . The recombinant expression system provides a means to produce sufficient quantities of the protein for structural analyses, functional assays, and potential therapeutic applications.
Potential Applications in Vaccine Development
Research into recombinant attenuated Y. pseudotuberculosis strains has shown promise for vaccine development. For example, a Y. pseudotuberculosis PB1+ strain (χ10069) with ΔyopK ΔyopJ Δasd triple mutations has been engineered to deliver Y. pestis fusion proteins as protective antigens against yersiniosis and plague .
While the search results do not specifically address the use of recombinant ArnE in vaccine development, its role in antimicrobial resistance suggests potential applications. Understanding the structure and function of ArnE could lead to the development of inhibitors targeting this protein, potentially restoring susceptibility to antimicrobial peptides in resistant strains.
Comparison with Related Bacterial Species
The arn operon components, including ArnE, appear to be functionally conserved across various Gram-negative bacterial species. For instance, the search results indicate that similar flippase subunits exist in Salmonella paratyphi A . The conservation of this pathway across different bacterial species highlights its evolutionary importance in bacterial survival and adaptation to environmental stresses, particularly exposure to antimicrobial compounds.
Studies with E. coli have demonstrated that the arn pathway is regulated by environmental factors, such as the presence of Fe³⁺, which promotes the accumulation of BP-Ara4N and BP-Ara4FN . Similar regulatory mechanisms likely exist in Y. pseudotuberculosis, although the specific details may vary between species.
The Role of ArnE in Polymyxin Resistance
Polymyxins are cyclic cationic antimicrobial peptides that disrupt bacterial membranes by binding to the negatively charged lipopolysaccharides. The modification of lipid A with Ara4N, facilitated by the Arn pathway including ArnE, reduces this negative charge and consequently decreases polymyxin binding.
Table 2: Comparison of ArnE-Related Antimicrobial Resistance in Different Bacterial Species
| Bacterial Species | Resistance Mechanism | Role of ArnE/Arn Pathway | Environmental Trigger |
|---|---|---|---|
| Y. pseudotuberculosis | LPS modification with Ara4N | BP-Ara4N translocation | Low Mg²⁺, Fe³⁺ exposure |
| E. coli | LPS modification with Ara4N | BP-Ara4N translocation | Fe³⁺ exposure |
| Salmonella paratyphi A | LPS modification with Ara4N | BP-Ara4N translocation | PhoP/PhoQ activation |
Gaps in Current Knowledge
Despite the importance of ArnE in antimicrobial resistance, several aspects of its function and regulation remain to be fully elucidated. Key areas for future research include:
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Detailed structural characterization of the ArnE/ArnF flippase complex
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Specific regulatory mechanisms controlling arnE expression in Y. pseudotuberculosis
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Potential interactions between ArnE and other components of the Arn pathway
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Development of specific inhibitors targeting ArnE function
Therapeutic Applications and Drug Development
The central role of ArnE in antimicrobial resistance makes it an attractive target for novel therapeutic strategies. Inhibition of ArnE function could potentially restore bacterial susceptibility to existing antimicrobial peptides, addressing a critical need in the face of increasing antibiotic resistance.
Furthermore, understanding the immunogenic properties of recombinant ArnE could contribute to vaccine development strategies. Similar approaches have been successfully employed with other Yersinia proteins, as demonstrated by the use of recombinant attenuated Y. pseudotuberculosis strains for vaccination against yersiniosis and plague .
Product Specs
Note: We will prioritize shipping the format currently in stock. However, if you have specific format requirements, please indicate them when placing your order, and we will accommodate your request.
Note: All our proteins are shipped with standard blue ice packs. If you require dry ice shipping, please communicate with us in advance, as additional fees will apply.
Generally, the shelf life of liquid form is 6 months at -20°C/-80°C. The shelf life of lyophilized form is 12 months at -20°C/-80°C.
Target Background
KEGG: ypb:YPTS_2400
Q&A
What is the functional role of ArnE in Y. pseudotuberculosis?
ArnE functions as a subunit of the flippase complex responsible for translocating 4-amino-4-deoxy-L-arabinose-phosphoundecaprenol across bacterial membranes. Similar to the P4-ATPase lipid flippases described in eukaryotes, these bacterial flippases maintain membrane asymmetry by facilitating the movement of specific lipid molecules from one leaflet to another within the membrane bilayer . In Y. pseudotuberculosis, this activity contributes to lipopolysaccharide (LPS) modification, which affects bacterial surface properties and interactions with host immune systems .
How does ArnE relate to other known bacterial flippases?
ArnE belongs to a family of membrane transport proteins that share functional similarities with eukaryotic P4-ATPases, although their structures differ significantly. While eukaryotic flippases like Drs2p-Cdc50p primarily transport phospholipids such as phosphatidylserine and phosphatidylethanolamine , bacterial flippases like ArnE specialize in translocating lipid A modifications such as 4-amino-4-deoxy-L-arabinose. These modifications are crucial for bacterial resistance to cationic antimicrobial peptides and certain antibiotics.
What genomic context surrounds the arnE gene in Y. pseudotuberculosis?
The arnE gene in Y. pseudotuberculosis is typically found within an operon containing other genes involved in LPS modification. These genes often include those responsible for the biosynthesis of 4-amino-4-deoxy-L-arabinose and its incorporation into lipid A. Understanding this genomic context is essential for designing targeted mutagenesis strategies and interpreting phenotypic changes when manipulating arnE expression .
What are effective strategies for creating arnE knockouts in Y. pseudotuberculosis?
Creating arnE knockouts in Y. pseudotuberculosis can be efficiently achieved using PCR-based procedures without cloning steps. The optimal approach involves generating PCR fragments carrying an antibiotic resistance gene flanked by regions homologous to the arnE locus (typically 500 bp for highest efficiency). These fragments can then be electroporated into Y. pseudotuberculosis strains expressing the homologous recombination system encoded by plasmid pKOBEG-sacB . Selection of transformants on antibiotic-containing media followed by PCR verification efficiently identifies successful knockout mutants. This method eliminates the need for suicide vector construction and multiple subcloning steps, significantly accelerating the mutagenesis process.
How can one express recombinant ArnE protein for functional studies?
Expression of recombinant ArnE requires careful consideration of membrane protein challenges. For Y. pseudotuberculosis proteins, a recommended approach involves constructing expression vectors containing the arnE gene with appropriate tags (His-tag or FLAG-tag) for purification. These constructs can be transformed into Y. pseudotuberculosis strains using electroporation methods as described for strain construction in previous studies . For expression, cultures should be grown at 28°C (optimal for Y. pseudotuberculosis) until reaching logarithmic phase (OD600 0.4-0.6), followed by induction with an appropriate inducer depending on the vector system used. Membrane fractions containing ArnE can be isolated using ultracentrifugation at 120,000 × g for 2 hours at 4°C, similar to protocols used for outer membrane vesicle isolation .
What control strains should be included when studying ArnE function?
When investigating ArnE function, multiple control strains should be included: 1) Wild-type Y. pseudotuberculosis expressing native levels of ArnE; 2) ArnE knockout strains (ΔarnE); 3) Complemented strains where the wild-type arnE gene is reintroduced into the knockout strain; and 4) Strains expressing site-directed mutants of key residues in ArnE. For constructing these strains, electrical conversion methods followed by antibiotic selection (typically using chloramphenicol at 50 μg/mL) and sucrose screening (LB agar with 10% sucrose) have proven effective for Y. pseudotuberculosis .
What approaches are recommended for determining ArnE topology and membrane integration?
Determining ArnE membrane topology requires a multi-faceted approach. Begin with computational prediction of transmembrane segments using algorithms like TMHMM and TopPred. These predictions should be experimentally validated using approaches such as: 1) Cysteine-scanning mutagenesis with membrane-impermeable thiol-reactive reagents; 2) Fusion reporter proteins (PhoA/LacZ) at various positions; and 3) Epitope insertion followed by immunofluorescence microscopy under permeabilized and non-permeabilized conditions. By comparing ArnE topology to characterized flippases like P4-ATPases, researchers can identify conserved structural features potentially involved in substrate recognition and translocation .
How can ArnE flippase activity be measured experimentally?
Measuring ArnE flippase activity presents considerable challenges due to the complex nature of its substrate. Recommended approaches include: 1) Reconstituting purified ArnE into proteoliposomes containing fluorescently labeled lipid analogs of 4-amino-4-deoxy-L-arabinose-phosphoundecaprenol; 2) Monitoring translocation using fluorescence quenching assays; and 3) Employing lipid mass spectrometry to track the movement of native substrates across membrane leaflets. When designing these assays, researchers should consider the structural features identified in other flippases, such as the importance of transmembrane segments 4 and 5, which contain residues crucial for substrate interaction in P4-ATPases (like Ile508, Lys1018 in Drs2p) .
What role does ArnE play in antimicrobial resistance mechanisms?
ArnE likely contributes to antimicrobial resistance by facilitating LPS modifications that reduce the negative charge of the bacterial outer membrane. This alteration decreases the binding affinity of cationic antimicrobial peptides and certain antibiotics to the bacterial surface. To study this function, researchers should conduct minimum inhibitory concentration (MIC) assays comparing wild-type, ΔarnE, and complemented strains against various antimicrobials. Additionally, membrane permeability assays using fluorescent dyes and outer membrane vesicle (OMV) analysis can provide insights into how ArnE-mediated lipid flipping affects membrane properties .
How can cryo-electron microscopy be applied to determine ArnE structure?
Cryo-electron microscopy (cryo-EM) represents a powerful approach for determining ArnE structure at near-atomic resolution. The methodology should follow protocols similar to those used for P4-ATPase structural studies : 1) Express and purify ArnE in complex with potential interacting partners using affinity chromatography and gel filtration; 2) Stabilize the protein in detergent micelles (LMNG has proven effective for membrane proteins) or nanodiscs; 3) Prepare vitrified samples on holey carbon grids; and 4) Collect and process data using 3D reconstruction techniques. For optimal results, researchers should consider capturing ArnE in different functional states using substrate analogs or ATP/ADP to understand the conformational changes associated with the flippase mechanism.
What approaches can identify ArnE interaction partners in the bacterial membrane?
Identifying ArnE interaction partners requires complementary approaches: 1) In vivo cross-linking with membrane-permeable crosslinkers followed by affinity purification and mass spectrometry; 2) Bacterial two-hybrid systems adapted for membrane proteins; and 3) Co-immunoprecipitation studies using epitope-tagged ArnE. Mass spectrometry analysis of purified complexes should employ stringent criteria (p-value filtering) to identify true interactions, followed by bioinformatic analysis to predict subcellular localization of identified proteins using tools like Gneg-mPLoc . These approaches will help determine whether ArnE functions independently or as part of a larger complex, similar to the Drs2p-Cdc50p interaction observed in eukaryotic P4-ATPases .
How can regulatory mechanisms controlling arnE expression be characterized?
To characterize regulatory mechanisms controlling arnE expression, researchers should implement: 1) Reporter gene fusions (lacZ, gfp) to the arnE promoter region to measure expression under various environmental conditions; 2) Chromatin immunoprecipitation (ChIP) to identify transcription factors binding to the arnE promoter; 3) RNA-seq analysis comparing transcriptomes under conditions that may trigger arnE expression (e.g., antimicrobial exposure, pH changes, host-like environments); and 4) CRISPR interference (CRISPRi) to systematically identify genes affecting arnE expression. These approaches will reveal how Y. pseudotuberculosis regulates arnE in response to environmental cues, potentially uncovering new therapeutic targets.
How can outer membrane vesicles (OMVs) be used to study ArnE function?
Outer membrane vesicles (OMVs) provide a valuable tool for studying ArnE function in a near-native environment. To apply this approach: 1) Generate Y. pseudotuberculosis strains with wild-type or modified arnE; 2) Extract OMVs using ultracentrifugation protocols (120,000 × g, 4°C for 2 hours) after initial bacterial removal by filtration through 0.22-μm filters; 3) Characterize OMVs by transmission electron microscopy (80kV, 25000X magnification) with negative staining (1-2% phosphotungstic acid); and 4) Analyze lipid composition using mass spectrometry . Comparing OMVs from wild-type versus arnE-modified strains can reveal how ArnE influences membrane composition and organization.
What animal models are appropriate for studying ArnE's role in virulence?
When studying ArnE's role in Y. pseudotuberculosis virulence, researchers should consider both mouse infection models and cell culture systems. For in vivo studies, compare colonization, dissemination, and survival rates between wild-type and ΔarnE strains following oral or intravenous inoculation. Complementary in vitro approaches should examine bacterial adhesion to epithelial cells, resistance to macrophage killing, and immune stimulation profiles. Importantly, researchers should assess how ArnE-dependent LPS modifications affect the immunostimulatory properties of Y. pseudotuberculosis and its OMVs, particularly regarding their ability to elicit protective immune responses against subsequent challenges .
How might ArnE inhibitors be designed and evaluated for therapeutic potential?
Developing ArnE inhibitors requires a systematic approach: 1) Perform in silico screening against structural models based on cryo-EM data or homology models derived from related flippases; 2) Evaluate promising compounds using in vitro flippase assays with reconstituted ArnE; 3) Assess cellular effects by measuring changes in LPS modification, membrane permeability, and antimicrobial susceptibility; and 4) Test synergy with existing antibiotics. When developing these inhibitors, researchers should consider targeting unique features of bacterial flippases that distinguish them from eukaryotic counterparts, similar to how the unique topology and regulatory mechanisms of P4-ATPases provide specific targeting opportunities .
What are the critical knowledge gaps in understanding ArnE function?
Despite advances in bacterial membrane biology, significant knowledge gaps remain regarding ArnE function: 1) The precise molecular mechanism of substrate recognition and translocation; 2) The energetics driving the flipping process (ATP-dependent vs. secondary active transport); 3) Regulatory networks controlling arnE expression in response to environmental cues; and 4) The full spectrum of physiological roles beyond antimicrobial resistance. Addressing these gaps will require combining structural biology, genetic manipulation, biochemical analyses, and in vivo infection models to build a comprehensive understanding of this important membrane protein.
How can high-throughput approaches accelerate ArnE research?
High-throughput approaches can significantly accelerate ArnE research through: 1) CRISPR-based genome-wide screens to identify genetic interactions with arnE; 2) Chemical genetic screens to discover small molecules affecting ArnE function; 3) Systematic mutagenesis combined with activity assays to map functional residues; and 4) Comparative genomics across Yersinia species and strains to understand evolutionary conservation and specialization. The PCR-based mutagenesis techniques described for Y. pseudotuberculosis are particularly amenable to high-throughput applications, allowing rapid and efficient large-scale mutagenesis of chromosomal targets .
