Recombinant Yersinia pestis Probable 4-amino-4-deoxy-L-arabinose-phosphoundecaprenol flippase subunit ArnE (arnE)
Description
Introduction to Yersinia pestis and Membrane Modification Systems
Yersinia pestis, the causative agent of plague, has severely affected human health since ancient times and remains endemic in regions of Africa, Asia, and the Americas. This Gram-negative bacterium transmits bubonic plague through infected flea bites, with the potential to develop into pneumonic plague, which is considered uniformly fatal . The remarkable virulence and historical impact of this pathogen have made it a significant focus of microbiological and infectious disease research.
Y. pestis employs sophisticated mechanisms to survive within host environments, including specific membrane modifications that contribute to immune evasion. Membrane remodeling is a hallmark of Y. pestis pathogenesis, particularly as it alternates between mammalian hosts (37°C) and the ambient temperatures (21-26°C) of arthropod transmission vectors or external environments . These temperature-dependent modifications affect the lipopolysaccharide (LPS) structure, specifically the lipid A portion, which is recognized by host immune receptors.
Role of Two-Component Systems in Y. pestis Virulence
Research has demonstrated that several two-component gene regulatory systems (TCSs) play crucial roles in Y. pestis survival within host environments. Among these systems, PhoPQ has been identified as particularly important for resistance to neutrophil bactericidal activity . The PhoPQ system contributes to Y. pestis survival in human neutrophils through a mechanism involving 4-amino-4-deoxy-L-arabinose (4-aminoarabinose) modification of lipid A . This modification represents a critical mechanism through which the bacterium resists antimicrobial peptides and survives immune cell attack.
The Arn Pathway and Lipid A Modification
The Arn (4-aminoarabinose) pathway consists of several enzymes that work collectively to synthesize and incorporate 4-aminoarabinose into lipid A. Within this pathway, ArnE functions specifically in the membrane translocation step, facilitating the flipping of 4-aminoarabinose-phosphoundecaprenol from the cytoplasmic to the periplasmic face of the inner membrane, where it becomes available for subsequent incorporation into lipid A.
| Protein | Function in Arn Pathway | Regulation |
|---|---|---|
| ArnA | Bifunctional enzyme: formyltransferase and decarboxylase activities | Regulated by PhoPQ TCS |
| ArnB | Aminotransferase | Regulated by PhoPQ TCS |
| ArnC | Undecaprenyl phosphate-aminoarabinose transferase | Regulated by PhoPQ TCS |
| ArnD | Deformylase | Regulated by PhoPQ TCS |
| ArnE | Flippase subunit (membrane translocation) | Regulated by PhoPQ TCS |
| ArnF | Flippase subunit (works with ArnE) | Regulated by PhoPQ TCS |
| ArnT | Aminoarabinose transferase (adds aminoarabinose to lipid A) | Regulated by PhoPQ TCS |
Contribution to Antimicrobial Peptide Resistance
The 4-aminoarabinose modification of lipid A, facilitated by ArnE and other components of the Arn pathway, significantly contributes to Y. pestis resistance against cationic antimicrobial peptides. This resistance mechanism is particularly important for survival within phagocytic cells such as neutrophils, which deploy various antimicrobial compounds to eliminate invading pathogens .
Relationship to PhoPQ Regulatory System
The PhoPQ two-component system has been identified as crucial for Y. pestis resistance to neutrophil bactericidal activity . The relationship between PhoPQ and ArnE is significant, as PhoPQ regulates the expression of the Arn pathway genes, including arnE. Research suggests that PhoP is important for Y. pestis survival in human neutrophils through mechanisms involving 4-aminoarabinose modification of lipid A . This modification represents a critical adaptation that enhances bacterial survival within host environments.
Evolutionary Context and Adaptation
Y. pestis has evolved numerous adaptations from its ancestor Yersinia pseudotuberculosis, including modifications to its membrane structure that promote immune evasion. While specific evolutionary changes in the ArnE protein have not been extensively characterized, research on related membrane remodeling systems in Y. pestis has revealed significant adaptations. For example, a single-nucleotide polymorphism in the lipid A acyltransferase pagP results in a premature stop in translation, yielding a truncated, nonfunctional enzyme that contributes to the synthesis of a "stealthy," hypoacylated lipid A structure absent in other Yersiniaceae . These evolutionary changes collectively contribute to Y. pestis pathogenicity and host immune evasion.
Recombinant Production and Availability
Recombinant Yersinia pestis Probable 4-amino-4-deoxy-L-arabinose-phosphoundecaprenol flippase subunit ArnE is commercially available through suppliers such as CUSABIO TECHNOLOGY LLC . These recombinant proteins serve as valuable research tools for studying bacterial membrane modifications, antimicrobial resistance mechanisms, and potential therapeutic targets.
Vaccine Research and Development
Research on recombinant Y. pestis antigens has shown significant promise for vaccine development. Studies have demonstrated that plant-derived purified recombinant plague antigens, when administered to guinea pigs, generate systemic immune responses and provide protection against aerosol challenges with virulent Y. pestis . While these studies have primarily focused on F1 and V antigens rather than ArnE specifically, they highlight the potential value of recombinant Y. pestis proteins for preventive medicine applications.
Genetic Manipulation and Functional Analysis
Understanding the role of ArnE in Y. pestis pathogenesis typically involves genetic manipulation approaches, including gene deletion and complementation studies. By generating arnE mutant strains and assessing their susceptibility to antimicrobial peptides and survival within immune cells, researchers can elucidate the specific contributions of this protein to bacterial virulence.
Product Specs
Please note that we will prioritize shipping the format currently available in stock. However, if you have a specific format preference, kindly indicate it in your order remarks and we will fulfill your request.
All our proteins are shipped with standard blue ice packs by default. If you require dry ice shipment, please communicate this to us in advance as additional fees will apply.
Generally, liquid forms have a shelf life of 6 months at -20°C/-80°C, while lyophilized forms have a shelf life of 12 months at -20°C/-80°C.
The tag type will be determined during the production process. If you have a specific tag type requirement, please inform us and we will prioritize developing the specified tag.
Target Background
KEGG: ypp:YPDSF_0733
Q&A
What is the functional role of ArnE in Yersinia pestis?
ArnE (previously known as PmrM) functions as a subunit of an undecaprenyl phosphate-α-L-Ara4N flippase. Its primary role involves transporting undecaprenyl phosphate-α-L-Ara4N across the inner membrane as part of the lipid A modification pathway. This modification with 4-amino-4-deoxy-L-arabinose (L-Ara4N) is required for resistance to polymyxin and cationic antimicrobial peptides, representing a critical bacterial defense mechanism. The modification process occurs on the outer surface of the inner membrane, with ArnE working together with ArnF (previously PmrL) to facilitate this transport function .
How does ArnE relate to the L-Ara4N modification pathway?
ArnE operates within a complex pathway that modifies lipid A with L-Ara4N. The pathway begins with UDP-glucose conversion to UDP-glucuronic acid, followed by oxidative decarboxylation by ArnA to generate UDP-4-ketopentose. ArnB then transaminated this intermediate to generate UDP-β-L-Ara4N, which is subsequently N-formylated by ArnA. ArnC transfers the N-formylated L-Ara4N to undecaprenyl phosphate, followed by deformylation by ArnD. At this point, ArnE and ArnF (the flippase subunits) transport the undecaprenyl phosphate-L-Ara4N to the outer surface of the inner membrane, where ArnT transfers the L-Ara4N group to lipid A .
How do ArnE and ArnF cooperate as flippase subunits?
The cooperation between ArnE and ArnF as flippase subunits involves a complex interaction that facilitates the translocation of undecaprenyl phosphate-α-L-Ara4N across the inner membrane. Research suggests these proteins function as a heterodimeric or potentially heteromultimeric complex. Experimental evidence using N-hydroxysulfosuccinimidobiotin labeling has implicated both ArnE (PmrM) and ArnF (PmrL) in this transport process, while ArnT is not involved in this specific membrane translocation step. Their functional relationship likely involves complementary domains that form a channel or flip-flop mechanism to move the lipid-linked substrate from the cytoplasmic leaflet to the periplasmic leaflet of the inner membrane .
What is the impact of ArnE mutations on antimicrobial resistance phenotypes?
Mutations in ArnE would likely disrupt the transport of undecaprenyl phosphate-α-L-Ara4N across the inner membrane, thereby preventing the modification of lipid A with L-Ara4N. Without this modification, Y. pestis would demonstrate increased susceptibility to polymyxin and other cationic antimicrobial peptides. Researchers investigating this phenomenon should employ site-directed mutagenesis targeting conserved residues in ArnE, followed by antimicrobial susceptibility testing using minimum inhibitory concentration (MIC) assays. Additionally, mass spectrometry analysis of lipid A would likely reveal a reduction or absence of L-Ara4N modifications in ArnE mutants compared to wild-type strains .
How does the expression of ArnE correlate with environmental stimuli?
The expression of ArnE and related proteins in the L-Ara4N modification pathway is likely regulated by environmental signals that indicate hostile conditions requiring increased antimicrobial resistance. These signals may include low Mg²⁺ concentrations, acidic pH, or the presence of cationic antimicrobial peptides. The regulation probably occurs through two-component systems such as PmrA/PmrB or PhoP/PhoQ. Researchers investigating this regulatory network should employ quantitative PCR (qPCR) to measure arnE transcript levels under various environmental conditions, complemented by reporter gene assays using the arnE promoter region fused to a reporter such as luciferase or GFP to visualize expression patterns in response to different stimuli .
What are the optimal conditions for reconstitution and storage of recombinant ArnE?
For optimal reconstitution of lyophilized recombinant ArnE, researchers should first centrifuge the vial briefly to collect the contents at the bottom. The protein should then be reconstituted in deionized sterile water to a concentration of 0.1-1.0 mg/mL. For long-term storage, it is recommended to add glycerol to a final concentration of 5-50% (with 50% being the standard recommendation) and create aliquots to avoid repeated freeze-thaw cycles. These aliquots should be stored at -20°C/-80°C, with an expected shelf life of approximately 12 months for lyophilized forms and 6 months for liquid forms. For working stocks, store aliquots at 4°C for no more than one week to maintain protein stability .
How can researchers effectively analyze ArnE-mediated flippase activity in vitro?
Analyzing ArnE-mediated flippase activity in vitro presents significant challenges due to the membrane-associated nature of the process. A recommended approach involves reconstituting purified ArnE and ArnF proteins into liposomes with fluorescently labeled lipid analogs that mimic undecaprenyl phosphate-α-L-Ara4N. Researchers can then monitor fluorescence changes as the labeled lipids are flipped from the inner to outer leaflet of the liposome. Alternative approaches include:
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Radiolabeled substrate tracking
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Mass spectrometry to detect substrate translocation
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FRET-based assays using appropriately labeled donor and acceptor molecules
The experimental setup should include negative controls (liposomes without ArnE/ArnF) and positive controls (liposomes with known flippases) .
What expression systems are most effective for producing functional recombinant ArnE?
| Expression System | Advantages | Limitations | Recommended for |
|---|---|---|---|
| Yeast (e.g., P. pastoris) | Post-translational modifications, proper folding of membrane proteins | Slower growth, complex media requirements | Functional studies requiring authentic protein structure |
| E. coli | Rapid growth, high yield, simple media | May form inclusion bodies, lacks some PTMs | Structural studies, antibody production |
| Insect cells | Advanced eukaryotic PTMs, good for toxic proteins | Higher cost, technical complexity | Complex membrane proteins requiring specific modifications |
| Mammalian cells | Most authentic PTMs and folding | Highest cost, lowest yield | Proteins requiring mammalian-specific modifications |
For membrane proteins like ArnE, detergent solubilization protocols must be optimized regardless of the expression system chosen. Initial screening with mild detergents such as DDM, LMNG, or Brij-35 is recommended .
How should researchers interpret discrepancies between in vitro and in vivo ArnE activity?
When encountering discrepancies between in vitro and in vivo ArnE activity, researchers should systematically evaluate several factors:
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Membrane environment differences: The artificial membrane environment in vitro may lack specific lipids or proteins that are essential for optimal ArnE function in vivo. Consider supplementing in vitro systems with extracted bacterial lipids or co-factors.
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Protein partners: ArnE functions with ArnF as a flippase complex and may interact with other proteins in the Arn pathway. Ensure that necessary protein partners are included in in vitro assays.
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Post-translational modifications: Verify whether ArnE undergoes post-translational modifications in vivo that might be absent in recombinant systems.
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Assay limitations: In vitro assays may not fully recapitulate the complexity of the bacterial membrane environment or the kinetics of substrate availability.
Researchers should employ complementary approaches, such as genetic complementation of arnE mutants with the recombinant protein, to bridge the gap between in vitro observations and in vivo functionality .
What analytical techniques best characterize the interaction between ArnE and ArnF?
To thoroughly characterize the interaction between ArnE and ArnF, researchers should employ multiple complementary techniques:
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Co-immunoprecipitation (Co-IP): Using antibodies against one protein to pull down potential complexes, followed by western blotting to detect the partner protein.
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Förster Resonance Energy Transfer (FRET): Tagging ArnE and ArnF with appropriate fluorophores to detect proximity-dependent energy transfer, indicative of protein-protein interaction.
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Bimolecular Fluorescence Complementation (BiFC): Splitting a fluorescent protein between ArnE and ArnF, with fluorescence only occurring upon interaction.
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Surface Plasmon Resonance (SPR): Measuring the binding kinetics and affinity between purified ArnE and ArnF proteins.
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Cross-linking coupled with mass spectrometry: Identifying specific residues involved in the interaction interface.
A comprehensive analysis would integrate data from multiple techniques to build a model of how these proteins interact to form a functional flippase unit .
How can researchers quantitatively assess the impact of ArnE-mediated lipid A modification on antimicrobial resistance?
To quantitatively assess the impact of ArnE-mediated lipid A modification on antimicrobial resistance, researchers should implement a multi-faceted approach:
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Minimum Inhibitory Concentration (MIC) Assays: Compare MIC values for polymyxin and other cationic antimicrobial peptides between wild-type, arnE knockout, and complemented strains. Calculate fold-changes in susceptibility.
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Time-Kill Kinetics: Measure bacterial survival over time when exposed to antimicrobials, comparing wild-type and arnE mutant strains.
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Mass Spectrometry Analysis: Quantify the percentage of lipid A molecules modified with L-Ara4N in different strains using MALDI-TOF or LC-MS/MS.
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Membrane Permeability Assays: Measure uptake of fluorescent dyes (e.g., propidium iodide) to assess membrane integrity after antimicrobial peptide treatment.
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Correlation Analysis: Plot the percentage of L-Ara4N-modified lipid A against MIC values to establish a quantitative relationship between modification levels and resistance.
This comprehensive analysis provides robust data on how ArnE function quantitatively impacts antimicrobial resistance through its role in lipid A modification .
