Recombinant Cricetulus griseus CD44 antigen (CD44)

How does CD44 from Cricetulus griseus compare to human CD44 in research applications?

The human CD44 gene contains 20 exons, with the standard form (CD44s) composed of exons 1-5 and 16-20 spliced together . While the core protein structure is conserved across species, species-specific variations exist particularly in the variable regions, affecting binding affinities and interaction profiles with hyaluronic acid and other ligands.

For cross-species applications, it's important to consider:

• Epitope conservation: Antibodies raised against human CD44 may have variable reactivity with hamster CD44

• Binding domain differences: Subtle sequence variations may affect binding studies

• Post-translational modification patterns: Glycosylation patterns may differ between species

When studying specific binding interactions or developing diagnostic tools, researchers should carefully evaluate whether human or hamster CD44 is more appropriate, particularly when translational applications are intended. Human CD44 variants (particularly CD44v) have been extensively studied in cancer research, while hamster CD44 may be preferred for certain fundamental binding studies or when working with hamster cell lines .

What expression systems are commonly used for producing Recombinant Cricetulus griseus CD44, and what are their relative advantages?

Multiple expression systems can be used to produce Recombinant Cricetulus griseus CD44, each with distinct advantages for different research applications:

According to available data, Recombinant Cricetulus griseus CD44 protein has been successfully produced in E. coli, particularly for the full-length mature protein (amino acids 23-362) with N-terminal His tags . The choice of expression system should align with the intended experimental objectives, balancing factors such as protein authenticity, yield requirements, and cost considerations .

What challenges exist in designing experiments with CD44 variant isoforms, and how can researchers address them?

Working with CD44 variant isoforms presents several significant challenges due to the complexity and heterogeneity of these proteins. CD44 undergoes extensive alternative splicing, particularly in the variable region encoded by exons 6-15 (v1-v10), leading to multiple variant isoforms with tissue-specific and context-dependent expression patterns .

Major challenges include:

• Isoform Specificity: Standard detection methods often fail to distinguish between specific CD44 variants. Researchers must design isoform-specific primers or antibodies that target unique variant exon junctions.

• Protein Complexity: CD44 variants undergo extensive post-translational modifications including glycosylation, which affects their molecular weight, solubility, and binding properties.

• Experimental Design: When designing recombinant CD44 variant constructs, researchers must carefully select which domains to include based on the specific research question.

Methodological solutions:

To overcome these challenges, researchers have successfully employed several approaches:

• Domain-specific construct design: As demonstrated in recent research, selecting specific amino acid residues from various areas of the CD44 extracellular domain regions to create synthetic proteins with desired properties. For example, one study designed a recombinant protein that included approximately 100 amino acids from the variable component of the CD44 extracellular domain to develop a diagnostic tool for breast cancer .

• Bioinformatic optimization: Using tools like Clustal W for sequence alignment to identify conserved regions, ProtParam for physicochemical characterization, and GOR-IV and I-TASSER for secondary and tertiary structure predictions before expression .

• Expression system selection: For variant isoforms with complex structures, mammalian expression systems often provide the most authentic post-translational modifications, though E. coli systems can work for certain applications where glycosylation is less critical .

• Validation protocols: Implementing multiple validation techniques including western blotting with isoform-specific antibodies, ELISA, and functional assays to confirm both the identity and activity of the recombinant variant .

The selection of appropriate controls, including both positive controls (known variant isoforms) and negative controls (standard CD44 isoforms lacking the variant of interest), is critical for experimental validation.

How can researchers effectively validate the biological activity of purified Recombinant CD44?

Validating the biological activity of purified Recombinant CD44 requires a multi-faceted approach to confirm both structural integrity and functional capacity. The following comprehensive validation strategy ensures that the recombinant protein accurately represents native CD44 activity:

1. Structural Validation:

• SDS-PAGE and Western Blotting: Confirm protein size and identity using antibodies against either CD44 epitopes or fusion tags (His-tag). A purified recombinant CD44 protein should show bands at the expected molecular weight (approximately 85-90 kDa for standard isoform or 12 kDa for synthetic constructs with specific domains) .

• Mass Spectrometry: Verify protein sequence and post-translational modifications.

• Circular Dichroism: Assess secondary structure elements to confirm proper protein folding.

2. Functional Validation:

• Hyaluronic Acid Binding Assays: As CD44's primary function involves binding to hyaluronic acid, solid-phase binding assays using immobilized hyaluronic acid can verify functionality.

• Cell Adhesion Assays: Test the ability of the recombinant protein to inhibit CD44-mediated cell adhesion when added in solution.

• Competitive Binding Assays: Measure displacement of labeled ligands by the recombinant protein.

3. Immunological Recognition:

• ELISA: Develop sandwich or competitive ELISA assays to measure binding activity and specificity. Recent research successfully employed ELISA to detect antibodies against recombinant CD44v protein in patient serum, demonstrating the utility of properly validated recombinant proteins .

• Immunoprecipitation: Confirm that the recombinant protein can be recognized and pulled down by relevant antibodies.

4. Application-Specific Validation:
For cancer research applications, validation may include:

• Binding to Cancer Cell Lines: Confirm binding to cell lines known to express CD44 receptors.

• Competitive Inhibition: Demonstrate that the recombinant protein can block binding of anti-CD44 antibodies to cancer cells.

• Diagnostic Potential: Evaluate correlation between recombinant CD44 reactivity and disease state in patient samples. Research has shown a significant link between CD44v serum levels and breast cancer prevalence, suggesting properly validated recombinant CD44 constructs have diagnostic value .

A comprehensive validation protocol reported in recent literature involved western blotting to confirm recombinant CD44v expression, followed by ELISA and immunohistochemistry assays to validate functionality in clinical samples. This multi-method approach established that the recombinant protein maintained stable structure with exposed antigenic domains .

How can researchers design recombinant CD44 constructs for targeted disease diagnostics?

Designing recombinant CD44 constructs for disease diagnostics, particularly for cancer detection, requires careful consideration of protein domains, expression systems, and validation methods. Recent research provides a methodological framework for creating effective diagnostic tools using CD44 variants:

Step 1: Domain Selection and Construct Design

• Identify disease-specific CD44 variant isoforms through literature review and expression data analysis

• Select specific regions of interest, particularly focusing on the variable component of the extracellular domain (CD44v)

• Design constructs containing approximately 100 amino acid residues from targeted regions

• Include appropriate fusion tags (e.g., His-tag) to facilitate purification

A successful approach demonstrated in recent research involved selecting a short common section of variable area exons from the extracellular domain of human CD44 containing the N-terminal 100 amino acid residues (441-540) with six His amino acids as a fusion tag at the C-terminus .

Step 2: Bioinformatic Analysis and Optimization

• Retrieve CD44 variant sequences from protein databases like UniProt

• Align sequences using software such as Clustal W to identify conserved regions

• Analyze physicochemical properties using tools like ProtParam (ExPASy server)

• Predict secondary and tertiary structures using GOR-IV and I-TASSER respectively

• Ensure that antigenic residues have VaxiJen cutoff values >0.5 for immunogenicity

Step 3: Expression and Purification

• Clone the designed sequence into an appropriate expression vector (e.g., pET28a)

• Transform into expression hosts (commonly E. coli BL21(DE3) for diagnostics)

• Express and purify using affinity chromatography (e.g., Ni-NTA for His-tagged proteins)

• Confirm purity by SDS-PAGE (typically 15% gels for smaller constructs)

Step 4: Validation for Diagnostic Applications

• Confirm identity by western blotting using antibodies against the fusion tag

• Develop ELISA methods to detect antibodies against the recombinant protein in patient samples

• Validate with immunohistochemistry to confirm recognition of the target in patient tissues

• Correlate diagnostic results with clinical outcomes to establish sensitivity and specificity

Research has demonstrated that assessing anti-CD44v antibodies with properly designed recombinant CD44v constructs can serve as a useful tool for identifying breast cancer in its early stages . One study showed that a 12 kDa fusion protein with a pI of 5.65 and high fraction of random coils (83.18%) was effective for diagnostic purposes, with exposed immunogenic regions that could interact with patient antibodies .

What are the optimal approaches for studying CD44-ligand interactions using recombinant proteins?

Studying CD44-ligand interactions requires specialized techniques that can capture both the specificity and kinetics of these molecular interactions. Here are the most effective methodological approaches when using recombinant CD44 proteins:

Surface Plasmon Resonance (SPR)

• Methodology: Immobilize purified recombinant CD44 (particularly the extracellular domain) on a sensor chip and flow potential ligands over the surface

• Advantages: Provides real-time binding kinetics (kon and koff rates), affinity constants (KD), and doesn't require ligand labeling

• Considerations: Ensure proper orientation of the immobilized CD44 to maintain native binding sites; the extracellular domain is critical as it interacts with the external microenvironment and senses external stimuli

Solid-Phase Binding Assays

• Methodology: Coat ELISA plates with recombinant CD44 or ligands (e.g., hyaluronic acid), then detect binding using labeled antibodies

• Advantages: Relatively simple, quantitative, and amenable to high-throughput screening

• Considerations: May not accurately reflect solution-phase binding dynamics

Fluorescence-Based Techniques

• Methodology: Label recombinant CD44 or ligands with fluorophores and measure binding through Fluorescence Resonance Energy Transfer (FRET) or Fluorescence Polarization (FP)

• Advantages: Can be performed in solution, providing more physiologically relevant conditions

• Considerations: Labeling may interfere with binding interfaces

Isothermal Titration Calorimetry (ITC)

• Methodology: Directly measure heat changes upon binding of CD44 to its ligands

• Advantages: Provides complete thermodynamic profile (ΔH, ΔS, and ΔG) without requiring labeling or immobilization

• Considerations: Requires relatively large amounts of purified protein

Cellular Binding Assays

• Methodology: Compete labeled natural ligands with recombinant CD44 for binding to cell surface receptors

• Advantages: More physiologically relevant than purely in vitro systems

• Considerations: Complex interpretation due to multiple potential interaction partners on cell surfaces

Optimizing Experimental Conditions:
When designing CD44-ligand interaction studies, several factors significantly impact experimental outcomes:

• Buffer composition: CD44-hyaluronic acid interactions are particularly sensitive to salt concentration; physiological conditions (150 mM NaCl) are recommended

• pH considerations: Maintain pH between 7.0-7.4 to reflect physiological conditions

• Protein presentation: For recombinant CD44, ensuring the extracellular domain is properly folded is critical since this domain interacts with the external microenvironment

• Construct design: For ligand specificity studies, standard CD44 (sCD44) and variant isoforms (CD44v) may exhibit different binding properties due to their structural differences

Recent studies have successfully employed combinations of these methods to characterize CD44-ligand interactions, with particular emphasis on understanding how the different domains contribute to binding specificity and affinity .

What are the most common challenges in expressing and purifying Recombinant Cricetulus griseus CD44, and how can researchers overcome them?

Expression and purification of Recombinant Cricetulus griseus CD44 present several technical challenges that researchers need to address for successful protein production. Here are the most common issues and effective solutions:

Challenge 1: Poor Solubility and Inclusion Body Formation
When expressed in E. coli, CD44 (particularly full-length protein) often forms inclusion bodies due to its transmembrane domains and complex folding requirements.

Solutions:

• Express only the extracellular domain to improve solubility

• Use solubility-enhancing fusion tags (SUMO, MBP, or TRX) in addition to His-tags

• Optimize induction conditions (reduce temperature to 16-18°C, use lower IPTG concentrations)

• For inclusion bodies, develop effective refolding protocols using gradual dialysis with decreasing concentrations of denaturants

Challenge 2: Low Expression Yields
CD44 can exhibit low expression levels in various systems, limiting purification yields.

Solutions:

• Optimize codon usage for the expression host

• Screen multiple expression strains (BL21(DE3), BL21(DE3)pLysS, Rosetta)

• For E. coli systems, consider using specialized media like Terrific Broth to enhance yield

• Use controlled expression systems with tunable promoters to balance expression level and solubility

Challenge 3: Protein Degradation
CD44 may undergo proteolytic degradation during expression and purification.

Solutions:

• Add protease inhibitors during all purification steps

• Keep samples cold (4°C) throughout the purification process

• Consider using protease-deficient expression strains

• Minimize purification time by optimizing protocols

Challenge 4: Purification Challenges with Ni-NTA Affinity Chromatography
His-tagged CD44 purification can be complicated by non-specific binding and elution issues.

Solutions:

• Include low concentrations of imidazole (10-20 mM) in binding and wash buffers to reduce non-specific binding

• Use gradient elution rather than step elution to improve purity

• Consider dual affinity tags for enhanced purity

• Follow affinity purification with additional polishing steps (ion exchange, size exclusion)

• Transform expression construct (e.g., pET28a-CD44) into E. coli BL21(DE3) using standard heat shock protocols

• Culture in enriched media (e.g., Terrific Broth) at 37°C until OD600 reaches 0.6-0.8

• Induce with IPTG at reduced temperature (18-25°C) for 16-18 hours

• Harvest cells and lyse with appropriate buffer containing protease inhibitors

• Purify using Ni-NTA affinity chromatography with optimized imidazole gradient

• Confirm purity by SDS-PAGE (typically using 15% gels for smaller constructs)

• Validate protein identity by western blotting using anti-His antibodies

This approach has successfully yielded fusion proteins with >85% purity as determined by SDS-PAGE .

How can researchers effectively use Recombinant Cricetulus griseus CD44 in cancer research models?

Recombinant Cricetulus griseus CD44 serves as a valuable tool in cancer research models, particularly for studying cell adhesion, migration, and the development of diagnostic approaches. Here are methodological approaches for effectively utilizing this recombinant protein in cancer research:

Development of Diagnostic Tools

CD44, especially its variant isoforms (CD44v), has shown significant potential as a cancer biomarker. Researchers can develop diagnostic tools using recombinant CD44 through:

• ELISA-based detection systems: Coating plates with recombinant CD44 to detect anti-CD44 antibodies in patient serum. Recent research demonstrated a significant correlation between CD44v serum antibody levels and breast cancer prevalence .

• Immunohistochemistry (IHC) applications: Developing detection systems using antibodies raised against recombinant CD44 to identify CD44-expressing cells in tissue samples. Polyclonal antibodies obtained from mice immunized with recombinant CD44v have successfully detected CD44v antigen in breast cancer patient tissues through IHC .

Cancer Stem Cell Research

CD44 serves as a tumor-associated marker and can be used to detect cancer stem cells, particularly in breast cancer :

• Competitive binding assays: Using recombinant CD44 to compete with cell surface CD44 for antibody or ligand binding

• In vitro models: Developing systems to study the role of CD44 in maintaining stemness properties

• Flow cytometry applications: Using labeled recombinant CD44 or anti-CD44 antibodies validated against recombinant protein to isolate CD44-positive cancer stem cell populations

Functional Studies of CD44-Mediated Processes

Recombinant CD44 enables mechanistic studies of CD44's role in cancer:

• Migration and invasion assays: Using recombinant CD44 to block endogenous CD44-ligand interactions

• Signal transduction studies: Examining how CD44 engagement affects downstream signaling pathways

• Adhesion inhibition: Blocking CD44-mediated adhesion to components of the extracellular matrix

Development of Therapeutic Strategies

Recombinant CD44 can facilitate the development of CD44-targeted therapies:

• Antibody screening: Identifying antibodies with high specificity and affinity for CD44

• Peptide development: Designing peptides that mimic CD44 binding domains

• Drug screening: Identifying small molecules that disrupt CD44-ligand interactions

Methodological Considerations:

When using recombinant CD44 in cancer research, several factors should be considered to optimize experimental outcomes:

• Isoform selection: CD44 standard isoform (CD44s) and variant isoforms (CD44v) may have different roles in cancer progression. For breast cancer studies specifically, CD44v has demonstrated greater diagnostic potential .

• Domain-specific effects: The extracellular domain of CD44 interacts with the external microenvironment and is critical for most cancer-related functions .

• Species considerations: While Cricetulus griseus (Chinese hamster) CD44 shares significant homology with human CD44, researchers should consider species-specific differences when translating findings to human cancer models.

• Validation protocols: All applications should include appropriate controls and validation steps, such as western blotting to confirm protein identity and ELISA to verify functional activity .

Research has demonstrated that assessments using recombinant CD44v can serve as a useful tool for identifying breast cancer in its early stages, potentially leading to better clinical outcomes .

What emerging applications of Recombinant CD44 show the most promise for advancing cancer diagnostics and therapeutics?

Recombinant CD44 research is evolving rapidly, with several promising directions that could significantly advance cancer diagnostics and therapeutics. Based on current research trends, these approaches show particular potential:

Multi-Epitope Diagnostic Platforms

Next-generation diagnostic tools combining multiple CD44 variant-specific domains in single recombinant constructs could enhance diagnostic sensitivity and specificity:

• Customized variant combinations: Designing recombinant proteins containing multiple CD44v domains specific to different cancer types

• Multiplexed detection systems: Developing panels that simultaneously detect antibodies against multiple CD44 variants

• Cancer subtype discrimination: Creating diagnostic tools that not only detect cancer but also help classify tumor subtypes based on CD44 variant expression patterns

Current research has demonstrated that recombinant proteins including the variable component of the CD44 extracellular domain can effectively detect antibodies in breast cancer patient serum . Future extensions of this approach could significantly enhance early cancer detection.

Therapeutic Targeting Strategies

Recombinant CD44 variants can serve as platforms for developing targeted cancer therapeutics:

• Decoy receptors: Engineering soluble CD44 ectodomains to act as molecular decoys, preventing ligand binding to cell-surface CD44

• CAR-T cell development: Using insights from recombinant CD44 binding studies to design chimeric antigen receptors targeting cancer-specific CD44 variants

• Antibody-drug conjugate (ADC) screening: Utilizing recombinant CD44 to identify antibodies with optimal binding properties for ADC development

Biomarker-Driven Personalized Medicine

Incorporating CD44 variant profiling into personalized medicine approaches:

• Treatment response prediction: Correlating CD44 variant expression patterns with therapeutic outcomes

• Recurrence monitoring: Developing liquid biopsy approaches using anti-CD44v antibodies as markers for minimal residual disease

• Combination biomarkers: Integrating CD44v with other cancer markers for improved prognostic accuracy

Research has shown that polyclonal antibodies against recombinant CD44v can detect the antigen in both patient serum and tissue samples, suggesting potential for minimally invasive monitoring .

Structural Biology and Drug Design

Advanced structural studies of recombinant CD44:

• Structure-guided therapeutics: Using high-resolution structures of CD44 variants to design small molecule inhibitors of specific CD44-ligand interactions

• Allosteric modulators: Identifying binding sites distant from the primary ligand-binding domain that could modulate CD44 function

• Domain-specific targeting: Designing drugs that selectively target cancer-specific CD44 domains while sparing normal tissue functions

Methodological Innovations:

Several technical advances will likely accelerate these applications:

• Enhanced protein engineering: Using computational design to optimize CD44 constructs for specific applications

• Advanced glycoengineering: Controlling post-translational modifications to create more homogeneous recombinant proteins

• In vivo models: Developing better animal models to test CD44-targeted therapies

Current research has already demonstrated that properly designed recombinant CD44v constructs with exposed antigenic domains can effectively interact with patient antibodies . These findings provide a foundation for the development of more sophisticated diagnostic and therapeutic approaches targeting CD44 in cancer.

The methodological approaches outlined in recent studies, including bioinformatic design, expression system optimization, and multi-modal validation, establish a framework that can be extended to these emerging applications .

What are the recommended validation methods for confirming the identity and activity of recombinant CD44 proteins?

A comprehensive validation strategy for recombinant CD44 proteins should include methods to confirm protein identity, purity, structural integrity, and functional activity. The following technical recommendations provide a systematic approach:

Identity and Purity Validation:

• SDS-PAGE Analysis

  • Run purified protein on 15% gels for smaller constructs or 10% gels for full-length proteins

  • Expected molecular weight: ~12 kDa for engineered constructs with selected domains or 85-90 kDa for standard CD44

  • Purity threshold: ≥85% as determined by densitometric analysis

• Western Blotting

  • Primary detection: Use antibodies against the fusion tag (e.g., anti-His tag)

  • Secondary confirmation: Use CD44-specific antibodies if available

  • Protocol details: Transfer to PVDF membrane, block with 5% BSA, incubate with appropriate antibodies, and develop using standard detection methods

• Mass Spectrometry

  • Method: MALDI-TOF or LC-MS/MS

  • Analysis: Peptide mass fingerprinting for identity confirmation

  • Applications: SDS-PAGE , Mass Spectrometry

Structural Validation:

• Secondary Structure Analysis

  • Circular Dichroism (CD) spectroscopy

  • Expected profile for recombinant CD44v: High fraction of random coils (83.18%) and low extended strand (16.82%)

• Tertiary Structure Assessment

  • Size Exclusion Chromatography (SEC) to confirm monomeric state

  • Dynamic Light Scattering (DLS) for hydrodynamic radius determination

  • Thermal stability assays (DSF/DSC) to assess folding quality

Functional Validation:

• Binding Assays

  • ELISA-based detection of interactions with known ligands

  • Surface Plasmon Resonance (SPR) for binding kinetics

  • Recommended controls: Include positive controls (known CD44 ligands) and negative controls (non-binding proteins)

• Immunological Recognition

  • ELISA to detect antibodies against the recombinant protein in relevant samples

  • Protocol: Coat plates with recombinant CD44, incubate with serum samples, detect with labeled secondary antibodies

  • Validation metric: Statistically significant difference between patient and control samples

• Tissue Binding Studies

  • Immunohistochemistry to confirm binding to relevant tissues

  • Recommended approach: Use antibodies raised against the recombinant protein to stain tissue sections

Validation Data Example:

A comprehensive validation protocol reported in recent literature for a recombinant CD44v construct included:

• SDS-PAGE and western blotting with anti-His antibodies

• ELISA to detect antibodies against the recombinant protein in patient serum

• Immunohistochemistry to confirm recognition of the target in patient tissues

This multi-modal approach confirmed both structural integrity and functional activity of the recombinant protein .

What bioinformatic tools and resources are most valuable for designing optimized CD44 constructs?

Designing optimized CD44 constructs requires sophisticated bioinformatic analysis to predict structure, function, and immunogenicity. The following tools and resources provide a comprehensive workflow for construct design:

Sequence Analysis and Domain Identification:

• UniProt (www.uniprot.org)

  • Primary resource for retrieving CD44 protein sequences (e.g., Human CD44: P16070)

  • Provides annotated information on domain organization and post-translational modifications

  • Used successfully in recent CD44v construct design

• Clustal W/Clustal Omega

  • Multiple sequence alignment for identifying conserved regions across species or isoforms

  • Essential for designing constructs with cross-species applications

  • Effectively used to find conserved areas of human CD44 in previous research

• BLAST (Basic Local Alignment Search Tool)

  • Homology searching to identify related sequences

  • Useful for comparing Cricetulus griseus CD44 with human counterparts

  • Helps avoid regions with high similarity to other proteins

Structural Prediction and Analysis:

• GOR-IV

  • Secondary structure prediction algorithm

  • Successfully used to predict secondary structure of recombinant CD44v, validating high fraction of random coils (83.18%) and low extended strand (16.82%)

• I-TASSER

  • Tertiary structure prediction through iterative threading

  • Provides multiple structural models with confidence scores

  • Effectively used to verify that immunogenic regions of designed constructs were exposed

• SWISS-MODEL

  • Homology modeling based on experimental structures

  • Particularly useful when templates with high sequence identity are available

Physicochemical Properties and Stability Analysis:

• ProtParam (ExPASy server)

  • Calculates physicochemical parameters (molecular weight, pI, extinction coefficient)

  • Provides stability estimates through aliphatic index and GRAVY values

  • Used to determine properties of recombinant CD44v (MW: 12 kDa, pI: 5.65, aliphatic index: 36.45)

• FoldX or Rosetta

  • Estimate protein stability changes upon mutation

  • Useful for optimizing solubility and stability

Immunogenicity and Epitope Prediction:

• VaxiJen

  • Antigen prediction based on physicochemical properties

  • Recommended cutoff value: >0.5 for immunogenic regions

  • Successfully applied in recombinant CD44v design to ensure antigenic residues were properly exposed

• BepiPred/DiscoTope

  • B-cell epitope prediction tools

  • Useful for designing immunogenic constructs for antibody production

Codon Optimization:

• GenScript OptimumGene™ or similar tools

  • Optimize codon usage for the selected expression system

  • Improve translation efficiency and expression levels

  • Particularly important for E. coli expression systems

Integrated Design Workflow:

Based on successful approaches in recent literature, an effective design workflow includes:

• Retrieve CD44 sequences from UniProt and align using Clustal W

• Identify regions of interest (e.g., variable component of extracellular domain)

• Select approximately 100 amino acid residues from target regions

• Analyze physicochemical properties using ProtParam

• Predict secondary structure using GOR-IV and tertiary structure using I-TASSER

• Validate immunogenicity using VaxiJen (cutoff >0.5)

• Add appropriate fusion tags (e.g., 6xHis) for purification

• Optimize codons for the selected expression system

• Verify final construct design for absence of internal restriction sites