Recombinant Shigella boydii serotype 4 Putative leucine efflux protein (leuE)
Description
Definition and Biological Context
The Recombinant Shigella boydii Serotype 4 Putative Leucine Efflux Protein (LeuE) is a 191-amino-acid polypeptide (aa 1–191) expressed in heterologous systems such as Escherichia coli, yeast, or mammalian cells . This protein originates from Shigella boydii serotype 4 (strain Sb227), a Gram-negative pathogen responsible for shigellosis, a diarrheal disease affecting primates . LeuE is implicated in leucine transport, though its exact mechanistic role in Shigella physiology remains understudied .
Key Features:
-
Sequence Homology: Shares >99% amino acid similarity with LeuE homologs across Shigella species (e.g., S. dysenteriae, S. flexneri) .
-
Expression Systems: Primarily produced in E. coli with N-terminal His-tags for purification .
Comparative Analysis of LeuE Across Shigella Species:
| Species | Amino Acid Range | Expression Host | Key Application |
|---|---|---|---|
| S. boydii serotype 4 | 1–191 | E. coli | Vaccine development |
| S. dysenteriae | 1–212 | E. coli | Pathogenicity studies |
Production and Purification Workflow
Recombinant LeuE is generated through standardized protocols :
-
Cloning: LeuE gene (NCBI Reference: WP_148722086.1) is inserted into plasmids (e.g., pRSETA for E. coli BL21 systems) .
-
Induction: Protein expression is induced using IPTG, yielding inclusion bodies.
-
Purification: Nickel-affinity chromatography under denaturing conditions (8 M urea), followed by dialysis for refolding .
-
Quality Control:
Functional Role and Pathogenic Implications
While direct evidence linking LeuE to Shigella virulence is limited, genomic studies suggest its role in nutrient uptake and stress response :
-
Leucine Efflux: Hypothesized to regulate intracellular leucine levels, potentially influencing bacterial survival in host environments .
-
Clade-Specific Variation: S. boydii genomes segregate into three phylogenomic clades, but LeuE is conserved across all clades, indicating functional essentiality .
Immunogenicity and Vaccine Development Potential
LeuE is marketed as a component for experimental vaccine formulations, though peer-reviewed data on its efficacy are sparse . Comparative studies of Shigella antigens highlight challenges:
-
Antigenic Competition: Dominant immune responses in Shigella target proteins like IpaB, VirG, or OmpA .
-
Cross-Reactivity: No studies confirm LeuE-specific antibody responses in humans or animal models.
Immunogenicity of Select Shigella Antigens:
| Antigen | Molecular Weight | Immune Response Observed | Cross-Reactivity |
|---|---|---|---|
| LeuE | ~22 kDa | Not reported | Unknown |
| IpaB | 62 kDa | Strong IgG/IgA | High |
| VirGα | 76 kDa | Protective in mice | Limited |
Research Gaps and Future Directions
-
Functional Validation: LeuE’s role in leucine transport or virulence requires direct experimental evidence (e.g., knockout studies).
-
Immunogenicity Profiling: Preclinical trials evaluating LeuE-specific antibody titers and protective efficacy are needed.
-
Structural Studies: Crystal structures or cryo-EM data would clarify LeuE’s mechanistic role.
Product Specs
Note: While we prioritize shipping the format currently in stock, please specify your preferred format in order notes for customized preparation.
Note: Standard shipping includes blue ice packs. Dry ice shipping requires prior arrangement and incurs additional charges.
The tag type is determined during production. If you require a specific tag, please inform us; we will prioritize its development.
Target Background
KEGG: sbo:SBO_1292
Q&A
What is the Shigella boydii serotype 4 leuE protein and what is its function?
The leuE protein (UniProt ID: Q321T8) is a putative leucine efflux protein found in Shigella boydii serotype 4. It consists of 191 amino acids and is believed to function in the transport of leucine across bacterial membranes. As a membrane protein, it likely plays a role in amino acid homeostasis and possibly contributes to bacterial survival mechanisms. The protein contains multiple transmembrane domains characteristic of transport proteins, suggesting its involvement in substrate translocation across cellular membranes .
What is the epidemiological significance of Shigella boydii serotype 4?
Shigella boydii serotype 4 represents 9.2% of S. boydii isolates identified in Bangladesh, making it the third most prevalent serotype among the 20 serotypes of S. boydii in the region. This contextualizes the importance of studying proteins like leuE in this particular serotype. The Global Enteric Multicenter Study (GEMS) has identified S. boydii in approximately 5.4% of all Shigella infections, with specific serotypes showing regional prevalence patterns . Understanding serotype-specific proteins may contribute to targeted interventions against shigellosis.
What are the optimal conditions for expressing recombinant Shigella boydii serotype 4 leuE protein in E. coli?
For optimal expression of recombinant leuE protein in E. coli, several parameters need careful optimization. The commercially available recombinant protein is expressed with an N-terminal His tag in E. coli . For laboratory expression, the following conditions typically yield good results:
| Parameter | Recommended Conditions |
|---|---|
| Expression vector | pET-based vectors with T7 promoter |
| E. coli strain | BL21(DE3) or Rosetta(DE3) for rare codon optimization |
| Induction | 0.5-1.0 mM IPTG when OD600 reaches 0.6-0.8 |
| Temperature | 16-20°C post-induction for membrane proteins |
| Duration | 16-18 hours post-induction |
| Media | LB supplemented with appropriate antibiotics |
Since leuE is a membrane protein, expression at lower temperatures post-induction helps reduce inclusion body formation and improves proper membrane integration .
What purification strategies are most effective for isolating high-purity recombinant leuE protein?
Purification of recombinant His-tagged leuE protein can be achieved using a multi-step approach:
-
Initial cell lysis using either sonication or pressure-based methods in a buffer containing mild detergents (e.g., 1% n-dodecyl β-D-maltoside or 1% Triton X-100) to solubilize membrane proteins
-
Immobilized metal affinity chromatography (IMAC) using Ni-NTA or Co-NTA resins
-
Size exclusion chromatography for further purification and buffer exchange
The commercial preparation achieves >90% purity as determined by SDS-PAGE . For research applications requiring ultra-high purity, additional ion-exchange chromatography may be employed as a polishing step. The choice of detergents is critical throughout the purification process to maintain protein stability and native conformation.
How should researchers optimize storage conditions to maintain leuE protein stability and activity?
Based on manufacturer recommendations for the recombinant protein, the following storage guidelines ensure optimal stability:
-
Store lyophilized protein at -20°C/-80°C upon receipt
-
After reconstitution, add glycerol to a final concentration of 50% for long-term storage at -20°C/-80°C
-
For working stocks, store aliquots at 4°C for up to one week
-
Avoid repeated freeze-thaw cycles as they significantly reduce protein stability
-
Store in Tris/PBS-based buffer containing 6% Trehalose at pH 8.0
For reconstitution, it is recommended to briefly centrifuge the vial prior to opening, then reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL. The addition of protease inhibitors may further enhance stability for sensitive applications.
How can the recombinant leuE protein be utilized in studying bacterial membrane transport mechanisms?
The recombinant leuE protein serves as a valuable model for investigating bacterial membrane transport mechanisms through several experimental approaches:
-
Liposome reconstitution assays to directly measure leucine transport rates and substrate specificity
-
Site-directed mutagenesis of conserved residues to identify functional domains involved in substrate recognition and translocation
-
Protein-protein interaction studies to identify potential partners in transport complexes
-
Structural studies using X-ray crystallography or cryo-EM to determine three-dimensional conformation
These approaches can provide insights into the bioenergetics of transport, substrate specificity, and regulatory mechanisms of bacterial amino acid efflux systems. The purified recombinant protein enables controlled in vitro systems that would be difficult to achieve in whole-cell studies .
What role might leuE play in antibiotic resistance mechanisms in Shigella boydii?
Though not directly implicated in conventional antibiotic resistance, efflux proteins like leuE may contribute to bacterial adaptation mechanisms that indirectly affect antimicrobial susceptibility. Several possible mechanisms include:
Research on Shigella species has revealed multiple independent acquisitions of antimicrobial resistance (AMR) determinants at a local level . While the specific contribution of leuE to AMR has not been established, membrane transporters often play supportive roles in bacterial stress responses that could enhance survival under antibiotic pressure.
What insights can leuE studies provide about Shigella boydii pathogenesis and host-pathogen interactions?
Studies of leuE can contribute to understanding Shigella boydii pathogenesis through several research avenues:
-
Investigation of how amino acid transport affects bacterial survival in host environments
-
Analysis of leuE expression patterns during different stages of infection
-
Examination of potential roles in acid resistance mechanisms during gastric passage
-
Exploration of leuE contribution to intracellular survival in macrophages or epithelial cells
Genomic studies of S. boydii have revealed distinct virulence profiles among different serotypes . The specific contribution of leuE to serotype 4 virulence remains to be fully characterized, but transport proteins often play supporting roles in bacterial adaptation to host environments.
What are common challenges in working with recombinant membrane proteins like leuE and how can they be addressed?
Membrane proteins present several technical challenges that researchers should anticipate:
| Challenge | Recommended Solution |
|---|---|
| Low expression yields | Optimize codon usage, use specialized expression strains, lower induction temperature |
| Protein aggregation | Screen different detergents for solubilization, use fusion tags that enhance solubility |
| Loss of native conformation | Include appropriate lipids in buffers, use mild detergents like DDM or LMNG |
| Functional assessment difficulties | Develop liposome reconstitution protocols, establish clear functional assays |
| Protein precipitation during concentration | Add stabilizers like glycerol or trehalose, determine optimal protein concentration range |
When working specifically with leuE, maintaining a Tris/PBS-based buffer system with 6% trehalose at pH 8.0 has been shown to enhance stability . Additionally, expression as a fusion protein with solubility-enhancing tags may improve yields and handling properties.
How can researchers troubleshoot poor reconstitution results with lyophilized leuE protein?
When encountering difficulties with protein reconstitution, consider the following troubleshooting approaches:
-
Ensure complete dissolution by gentle agitation rather than vigorous vortexing
-
Centrifuge the vial before opening to bring all lyophilized material to the bottom
-
Use the recommended reconstitution buffer (deionized sterile water) initially, then adjust conditions if needed
-
Allow adequate time for complete rehydration (15-30 minutes at room temperature)
-
Filter the reconstituted protein through a 0.22 μm filter if visible particulates persist
-
Add glycerol gradually while gently mixing to avoid precipitation when preparing for long-term storage
If precipitation occurs despite these precautions, try reconstituting at a lower concentration initially (0.1 mg/mL) and gradually concentrating if necessary.
How might comparative genomic approaches advance our understanding of leuE evolution and function across Shigella species?
Comparative genomic analysis of leuE across Shigella species and serotypes could reveal evolutionary patterns and functional adaptations. With genomic data becoming increasingly available for Shigella isolates , researchers can:
-
Trace the evolutionary history of leuE genes across the Shigella genus
-
Identify conserved domains that suggest functional importance
-
Detect signatures of positive selection that might indicate adaptation to specific niches
-
Compare leuE variants between serotypes to correlate with pathogenicity patterns
Such analyses could determine whether leuE variants contribute to the distinct epidemiological profiles observed among Shigella species, where S. boydii demonstrates patterns of long-term colonization in endemic regions, similar to pathogenic E. coli variants .
What novel approaches could be developed for using leuE as a diagnostic or therapeutic target?
Innovative approaches for leveraging leuE in diagnostics or therapeutics might include:
-
Development of serotype-specific antibodies against unique epitopes of the leuE protein for diagnostic applications
-
Design of small-molecule inhibitors targeting leuE function as potential antimicrobial adjuvants
-
Exploration of leuE as a vaccine component, particularly if surface-exposed epitopes are identified
-
Incorporation of leuE detection in phage-based diagnostic systems, similar to approaches developed for other Shigella serotypes
While phage-based diagnostics have been developed for S. boydii type 1 , expanding such approaches to include markers for serotype 4 could enhance diagnostic capabilities, particularly in regions where this serotype is prevalent.
How might structural biology techniques advance our understanding of leuE function and regulation?
Advanced structural biology techniques could provide critical insights into leuE function:
-
Cryo-electron microscopy to visualize the three-dimensional arrangement of leuE within the membrane
-
X-ray crystallography to determine high-resolution structures, potentially in different conformational states
-
Hydrogen-deuterium exchange mass spectrometry to map dynamic regions involved in substrate binding
-
Molecular dynamics simulations to model transport mechanisms and substrate interactions
Structural determination would be particularly valuable for understanding the transport cycle, substrate specificity determinants, and potential sites for inhibitor binding. Such information could guide rational design of molecules targeting this transport system in pathogenic Shigella strains.
