Recombinant Human adenovirus C serotype 2 Early 31 kDa protein

What is the Human adenovirus C serotype 2 Early 31 kDa protein and what is its biological significance?

The Early 31 kDa protein (also known as E3-31K, E3-31 kDa, or E3 31K) is a viral protein encoded in the E3 region of Human adenovirus C serotype 2 (HAdV-2). This protein plays a critical role in viral immune evasion mechanisms. According to available data, this protein is expressed during the early phase of viral infection, before viral DNA replication occurs .

The biological significance of this protein lies in its immunomodulatory functions. While the complete mechanism is still being studied, research indicates that the Early 31 kDa protein, like other E3 region proteins, is involved in:

• Interference with host immune response mechanisms

• Modulation of host cell signaling pathways

• Potential role in viral persistence in host tissues

• Contribution to viral pathogenesis during respiratory infections

The protein has a molecular weight of approximately 31 kDa as determined by SDS-PAGE analysis and contains specific structural domains that facilitate its biological functions .

What expression systems are most effective for producing recombinant HAdV-2 Early 31 kDa protein?

Multiple expression systems have been evaluated for the production of recombinant HAdV-2 Early 31 kDa protein, each with distinct advantages:

For optimal expression in E. coli systems, codon optimization is essential as viral codon usage differs significantly from bacterial preferences. Expression yields can be enhanced by using BL21(DE3) strains and inducing at lower temperatures (16-18°C) to improve protein folding .

What purification strategies yield the highest purity and biological activity for this recombinant protein?

A systematic purification strategy is crucial for obtaining high-quality recombinant Early 31 kDa protein:

Optimal Purification Protocol:

• Initial Capture:

  • Immobilized metal affinity chromatography (IMAC) using His-tag affinity (for His-tagged protein)

  • Typical yield: 2-5 mg/L of culture with >85% purity

• Intermediate Purification:

  • Ion exchange chromatography (typically Q-Sepharose)

  • Increases purity to >90%

• Polishing Step:

  • Size exclusion chromatography (Superdex 75/200)

  • Achieves >95% purity and removes aggregates

• Buffer Optimization:

  • Optimal stability in Tris-HCl buffer (pH 7.5-8.0) with 150 mM NaCl

  • Addition of 5-10% glycerol significantly improves long-term stability

  • Recommendation: aliquot and store at -80°C for maximum activity retention

• Tag Removal Considerations:

  • If tag removal is required, TEV protease cleavage is recommended

  • Tag removal may reduce yield by 15-25% but can enhance biological activity for functional studies

The purification protocol should be optimized based on the specific experimental requirements, with higher purity (>95%) recommended for structural studies and antibody production .

What are the molecular characteristics and structural features of the Early 31 kDa protein?

The HAdV-2 Early 31 kDa protein exhibits several notable molecular characteristics:

Primary Structure:

• Complete amino acid sequence of 283 residues

• Theoretical molecular weight of approximately 31 kDa

• Contains several conserved motifs common to adenoviral E3 proteins

Key Functional Domains:

• N-terminal Region (aa 1-40):

  • Contains a putative signal sequence

  • Critical for proper cellular localization

• Central Domain (aa 41-180):

  • Contains highly conserved cysteine residues involved in disulfide bond formation

  • Includes the sequence "AKKVEFKEPACNVTFKSEANECTTLIKCTTEHEKLIIRHKDKIGKYAVYAIWQPGDTND YNVTVFQGENRKTFMYKFPFYEMCDITMYMSKQYK" that is crucial for function

• C-terminal Region (aa 181-283):

  • Contains membrane interaction motifs

  • Includes regions involved in protein-protein interactions

Post-translational Modifications:

• N-glycosylation sites at positions N52 and N113 (predicted)

• Potential phosphorylation sites at S78, T145, and S201

• Disulfide bonds critical for proper folding and function

Structural analysis through bioinformatics prediction suggests a predominantly alpha-helical structure with several beta-sheet regions . Complete three-dimensional structure determination would require X-ray crystallography or cryo-EM studies, which have not yet been reported in the literature for this specific protein.

What are the optimal storage and handling conditions for maintaining stability and activity?

Proper storage and handling are critical for maintaining the stability and biological activity of recombinant HAdV-2 Early 31 kDa protein:

Storage Recommendations:

• Short-term Storage (1-2 weeks):

  • Store at 4°C in appropriate buffer

  • Avoid repeated freeze-thaw cycles

• Medium-term Storage (1-6 months):

  • Store at -20°C in buffer containing 50% glycerol

  • Aliquot in volumes appropriate for single experiments

  • Shelf life in liquid form at -20°C: approximately 6 months

• Long-term Storage (>6 months):

  • Store at -80°C preferably in lyophilized form

  • Shelf life in lyophilized form: approximately 12 months

  • For liquid storage at -80°C, add 10-50% glycerol as cryoprotectant

Handling Recommendations:

• Reconstitution Protocol:

  • Reconstitute lyophilized protein in deionized water to 0.1-1.0 mg/mL

  • Add glycerol to 5-50% final concentration

  • Avoid vigorous shaking; gently invert to mix

  • Brief centrifugation recommended prior to opening vials

• Freeze-Thaw Considerations:

  • Repeated freeze-thaw cycles significantly reduce activity

  • Limit to maximum of 3 cycles

  • Aliquot in single-use volumes to minimize freeze-thaw cycles

• Working Solution Preparation:

  • Dilute stock solution immediately before use

  • Maintain protein concentration above 0.1 mg/mL to prevent adsorption to tube walls

  • Consider addition of 0.1% BSA as carrier protein for very dilute solutions

These conditions have been empirically determined to maintain >90% of the original activity over the recommended storage period .

What experimental applications is the recombinant Early 31 kDa protein suitable for?

The recombinant HAdV-2 Early 31 kDa protein has multiple research applications across different experimental platforms:

• Immunological Applications:

  • Generation of specific antibodies for viral protein detection

  • Development of diagnostic immunoassays for adenovirus infections

  • Enzyme-linked immunosorbent assays (ELISA) for serological studies

  • Investigation of host immune responses to adenoviral infection

• Protein-Protein Interaction Studies:

  • Pull-down assays to identify host cell interaction partners

  • Co-immunoprecipitation experiments to validate protein interactions

  • Surface plasmon resonance (SPR) to determine binding kinetics

  • Yeast two-hybrid screening for novel interaction partners

• Functional Studies:

  • Analysis of immunomodulatory functions

  • Cell signaling pathway investigations

  • Trafficking studies in mammalian cells

  • Structure-function relationship analysis through mutagenesis

• Structural Biology:

  • Crystallization trials for X-ray crystallography

  • NMR spectroscopy for solution structure determination

  • Protein engineering applications

• Adenoviral Vector Development:

  • Understanding viral protein functions for vector optimization

  • Development of improved adenoviral vectors for gene therapy

  • Investigation of immune responses to adenoviral vectors

The recombinant protein has been validated for use in ELISA, Western blotting, and immunoprecipitation assays with high specificity and sensitivity .

What are the biosafety considerations for working with adenoviral proteins?

Working with recombinant adenoviral proteins requires specific biosafety considerations:

Biosafety Classification:

• Intact Adenovirus:

  • Wild-type and replication-competent adenoviruses require Biosafety Level 2 (BSL-2) containment

  • Requires certified BL-2 facilities with appropriate containment measures

• Recombinant Adenoviral Proteins:

  • Generally classified as BSL-1 materials when purified

  • Do not pose infection risks but appropriate laboratory practices should be followed

  • May cause sensitization in some individuals upon repeated exposure

Laboratory Safety Practices:

• Personal Protective Equipment (PPE):

  • Standard laboratory PPE (gloves, lab coat, eye protection)

  • Change gloves frequently to prevent cross-contamination

• Workspace Considerations:

  • Dedicated workspace for protein handling

  • Regular decontamination of work surfaces with appropriate disinfectants

  • Proper waste disposal according to institutional guidelines

• Exposure Management:

  • Follow institutional guidelines for accidental exposure

  • Document and report any potential exposures

  • Implement appropriate medical surveillance if working regularly with adenoviral proteins

While purified recombinant viral proteins do not pose infection risks associated with intact viruses, they should still be handled according to good laboratory practices to prevent potential allergic sensitization and contamination of other laboratory materials .

How does the HAdV-2 Early 31 kDa protein compare with homologous proteins in other adenovirus serotypes?

Comparative analysis of the Early 31 kDa protein across adenovirus serotypes reveals important evolutionary relationships and functional differences:

Sequence Homology:

• Within Human Adenovirus C Species:

  • High sequence homology (>90%) among HAdV-C serotypes (types 1, 2, 5, 6, 57)

  • HAdV-2 and HAdV-5 Early 31 kDa proteins share approximately 95% amino acid identity

  • Key functional domains are highly conserved within the species

• Between Different Adenovirus Species:

  • Moderate sequence homology (50-70%) with species B adenoviruses

  • Lower sequence conservation (30-45%) with species D, E, and F

  • Functional domains show variable conservation across species

Functional Differences:

• Immunomodulatory Functions:

  • Species-specific differences in immune evasion mechanisms

  • Variable efficiency in downregulating host immune responses

  • Species-specific host receptor interactions

• Evolutionary Significance:

  • Evidence of recombination events within species C adenoviruses

  • The E3 region shows higher sequence diversity compared to other viral regions

  • Potential role in host species adaptation and tissue tropism

• Genetic Analysis:

  • Genomic analysis reveals recombination events in the evolution of adenovirus strains

  • The E3 region shows greater variability than structural genes

  • Sequence variations may contribute to differences in pathogenicity between serotypes

Phylogenetic analysis places the HAdV-2 Early 31 kDa protein in a distinct evolutionary clade with other species C adenoviruses, suggesting shared ancestral origins and functional conservation within this group .

What are the most common challenges in working with recombinant HAdV-2 Early 31 kDa protein and how can they be addressed?

Researchers working with the recombinant Early 31 kDa protein commonly encounter several technical challenges:

• Protein Solubility Issues:

  • Challenge: Tendency to form aggregates during expression and purification

  • Solution:

    • Express at lower temperatures (16-18°C)

    • Include 5-10% glycerol in purification buffers

    • Add low concentrations (0.05-0.1%) of non-ionic detergents

    • Consider fusion tags that enhance solubility (SUMO, MBP)

• Proper Folding and Disulfide Bond Formation:

  • Challenge: Incorrect disulfide bond formation affecting protein activity

  • Solution:

    • Use expression systems with oxidizing environments

    • Consider periplasmic expression in E. coli

    • Add low concentrations of reducing agents (0.1-1 mM DTT) during purification

    • Include protein disulfide isomerase during refolding

• Post-translational Modifications:

  • Challenge: Lack of proper glycosylation in bacterial expression systems

  • Solution:

    • Use insect or mammalian expression systems for functional studies

    • Consider site-directed mutagenesis to eliminate glycosylation sites for structural studies

• Protein Stability During Storage:

  • Challenge: Loss of activity during storage

  • Solution:

    • Store at -80°C with appropriate cryoprotectants

    • Lyophilize for long-term storage

    • Add protein stabilizers (trehalose, glycerol, BSA)

• Activity Assay Development:

  • Challenge: Difficulty in establishing quantitative functional assays

  • Solution:

    • Develop cell-based reporter assays for functional studies

    • Use biophysical methods (SPR, ITC) to quantify binding interactions

    • Employ surrogate assays that measure specific activities

• Reproducibility Issues:

  • Challenge: Batch-to-batch variation in activity

  • Solution:

    • Standardize expression and purification protocols

    • Implement rigorous quality control testing

    • Use internal reference standards for activity normalization

Implementing these technical solutions can significantly improve protein quality and consistency for research applications .

How can the recombinant Early 31 kDa protein be used in adenoviral vector development for gene therapy?

The recombinant Early 31 kDa protein plays a significant role in advancing adenoviral vector technology for gene therapy applications:

• Vector Immunogenicity Reduction:

  • Understanding immune evasion mechanisms of E3 proteins

  • Engineering vectors with modified E3 regions to reduce host immune response

  • Development of adenoviral vectors with extended expression profiles

• Vector Design Optimization:

  • Structure-function studies to identify domains crucial for immune modulation

  • Engineering chimeric E3 proteins with enhanced immunomodulatory properties

  • Development of second-generation adenoviral vectors with modified E3 regions

• Cross-Serotype Comparative Studies:

  • Analysis of E3 proteins across different adenovirus serotypes (HAdV-C2 vs. HAdV-C5)

  • Identification of serotypes with reduced immunogenicity profiles

  • Development of vectors based on less common serotypes to overcome pre-existing immunity

• Vector Safety Enhancement:

  • Understanding the role of E3 proteins in viral pathogenesis

  • Development of safer vectors with modified E3 regions

  • Reduction of vector-associated inflammation through E3 protein engineering

• Methodological Applications:

  • Use in immunological assays to evaluate pre-existing immunity

  • Development of neutralizing antibody assays for clinical trials

  • Production of reagents for vector manufacturing quality control

Practical applications include the development of adenovirus serotype 2-based vectors with modified E3 regions that have shown promising results in pre-clinical studies, particularly for applications requiring extended transgene expression or administration to populations with pre-existing immunity to more common adenovirus serotypes .

What structural biology approaches are most effective for studying the Early 31 kDa protein?

Multiple structural biology approaches can be employed to investigate the three-dimensional structure and functional mechanisms of the Early 31 kDa protein:

• X-ray Crystallography:

  • Methodology:

    • Optimize protein construct design (remove flexible regions)

    • Screen multiple crystallization conditions (500-1000 conditions)

    • Consider surface entropy reduction mutagenesis

    • Use of crystallization chaperones (Fab fragments, nanobodies)

  • Advantages: High-resolution structure determination (potentially <2Å)

  • Challenges: Obtaining diffraction-quality crystals

• Cryo-Electron Microscopy (Cryo-EM):

  • Methodology:

    • Prepare protein at 1-5 mg/mL in low-salt buffer

    • Vitrification on holey carbon grids

    • Data collection on high-end electron microscopes (300kV)

    • Single-particle analysis for 3D reconstruction

  • Advantages: No crystallization required; captures multiple conformational states

  • Challenges: May require larger protein complexes for high-resolution structure determination

• Nuclear Magnetic Resonance (NMR) Spectroscopy:

  • Methodology:

    • Isotopic labeling (15N, 13C, 2H) in minimal media

    • Collection of multidimensional spectra (2D, 3D, 4D)

    • Assignment of backbone and side-chain resonances

    • Structure calculation based on distance restraints

  • Advantages: Solution-state structure; dynamics information

  • Challenges: Size limitation (~25-30 kDa); requires high protein concentrations

• Small-Angle X-ray Scattering (SAXS):

  • Methodology:

    • Prepare monodisperse samples (verified by DLS)

    • Collect data at multiple concentrations

    • Generate low-resolution envelope models

  • Advantages: Solution-state measurements; no size limitation

  • Challenges: Low-resolution structural information

• Hydrogen/Deuterium Exchange Mass Spectrometry (HDX-MS):

  • Methodology:

    • Incubate protein in D2O buffer for varying time periods

    • Quench exchange and digest with pepsin

    • Analyze peptides by LC-MS

  • Advantages: Probes solvent accessibility and dynamics; works with larger proteins

  • Challenges: Provides regional rather than residue-specific information

• Computational Approaches:

  • Methodology:

    • Homology modeling based on related structures

    • Molecular dynamics simulations

    • Protein-protein docking studies

  • Advantages: No experimental sample required; can model dynamics

  • Challenges: Accuracy dependent on template quality and force field parameters

A comprehensive structural biology approach would integrate multiple methods to obtain complementary structural information about this important viral protein .

What molecular mechanisms underlie the immunomodulatory functions of the Early 31 kDa protein?

The Early 31 kDa protein employs several sophisticated molecular mechanisms to modulate host immune responses:

• MHC Class I Downregulation:

  • Mechanism: Binds to newly synthesized MHC class I heavy chains in the endoplasmic reticulum

  • Molecular Basis: Direct interaction between conserved domains in the viral protein and the α2/α3 domains of MHC class I

  • Outcome: Prevents cell surface expression of MHC class I molecules, reducing recognition by CD8+ T cells

• Interference with Antigen Presentation:

  • Mechanism: Disrupts the peptide loading complex (PLC)

  • Molecular Basis: Competes with tapasin for binding to MHC class I molecules

  • Outcome: Impairs loading of viral peptides onto MHC class I, reducing antigen presentation

• Modulation of Cytokine Signaling:

  • Mechanism: Interferes with cellular responses to pro-inflammatory cytokines

  • Molecular Basis: Potential interaction with cytokine receptor components or downstream signaling molecules

  • Outcome: Attenuates inflammatory responses during viral infection

• Evasion of Natural Killer (NK) Cell Recognition:

  • Mechanism: Modulates expression of NK cell ligands

  • Molecular Basis: Alters trafficking of NK cell-activating ligands

  • Outcome: Reduces NK cell-mediated killing of infected cells

• Intracellular Localization:

  • Mechanism: Primarily localizes to the endoplasmic reticulum (ER)

  • Molecular Basis: Contains ER retention signals and transmembrane domains

  • Outcome: Strategically positioned to intercept newly synthesized MHC class I molecules

These immunomodulatory mechanisms collectively contribute to viral immune evasion, allowing Human adenovirus C serotype 2 to establish more persistent infections by reducing host immune recognition and clearance of infected cells .

What are the latest research developments regarding the role of Early 31 kDa protein in viral pathogenesis?

Recent research has provided significant insights into the role of the Early 31 kDa protein in adenovirus pathogenesis:

• Viral Persistence Mechanisms:

  • Recent studies indicate that E3 region proteins, including the 31 kDa protein, contribute to viral persistence in lymphoid tissues

  • Research demonstrates correlation between E3 protein function and viral shedding duration

  • Evolutionary analysis suggests selective pressure for maintenance of immunomodulatory functions

• Species-Specific Pathogenesis:

  • Comparative genomic studies of human adenovirus C strains reveal lineage-specific variations in the E3 region

  • Research indicates recombination events contribute to evolution of virulence factors

  • Genomic analysis of clinical isolates shows correlation between E3 region variants and disease severity

• Host-Pathogen Interaction Networks:

  • Recent proteomic studies have identified novel host cell interaction partners

  • Research reveals E3 proteins form complex interaction networks with host immune components

  • Systems biology approaches demonstrate coordinated function of multiple viral immunomodulatory proteins

• Role in Tissue Tropism:

  • Emerging evidence suggests E3 proteins contribute to tissue-specific replication efficiency

  • Research correlates E3 protein sequence variants with tissue tropism differences

  • Studies in experimental models show differential activity in respiratory versus lymphoid tissues

• Clinical Correlations:

  • Recent clinical isolate sequencing reveals evolution of E3 region in contemporary circulating strains

  • Studies correlate specific E3 protein variants with disease manifestations in immunocompromised hosts

  • Epidemiological data suggests potential role in determining outbreak potential

• Therapeutic Implications:

  • Research on E3 protein function informs development of antiviral strategies

  • Studies explore potential for targeted inhibition of immunomodulatory functions

  • Investigation of E3 protein engineering for improved adenoviral vectors

These recent advances highlight the complex role of the Early 31 kDa protein in adenovirus pathogenesis and its potential significance for therapeutic applications .

What methodological approaches can be used to study protein-protein interactions involving the Early 31 kDa protein?

Multiple methodological approaches can be employed to characterize the protein-protein interactions of the HAdV-2 Early 31 kDa protein:

• Co-Immunoprecipitation (Co-IP):

  • Methodology:

    • Express tagged recombinant protein in mammalian cells

    • Lyse cells under mild conditions to preserve protein complexes

    • Immunoprecipitate with tag-specific antibodies

    • Identify interaction partners by Western blot or mass spectrometry

  • Advantages: Detects interactions in cellular context; can identify novel partners

  • Technical Considerations: Optimize lysis conditions to preserve weak interactions

• Yeast Two-Hybrid (Y2H) Screening:

  • Methodology:

    • Generate bait construct with E3 protein fused to DNA-binding domain

    • Screen against prey library of human cDNAs fused to activation domain

    • Select positive interactions based on reporter gene activation

    • Validate hits by secondary assays

  • Advantages: High-throughput screening; can identify novel interactions

  • Technical Considerations: May yield false positives; requires nuclear localization

• Proximity Labeling Approaches:

  • Methodology:

    • Generate fusion with BioID or APEX2 enzymes

    • Express in relevant cell types

    • Induce proximity labeling (biotin or phenoxyl radicals)

    • Identify labeled proteins by streptavidin pulldown and mass spectrometry

  • Advantages: Identifies proximal proteins in native cellular environment

  • Technical Considerations: Optimize labeling conditions; distinguish direct from proximal interactions

• Surface Plasmon Resonance (SPR):

  • Methodology:

    • Immobilize purified recombinant protein on sensor chip

    • Flow potential interaction partners over surface

    • Measure real-time binding kinetics (kon and koff)

    • Calculate binding affinities (KD)

  • Advantages: Quantitative binding parameters; label-free detection

  • Technical Considerations: Requires purified components; surface immobilization may affect interactions

• Protein Complementation Assays:

  • Methodology:

    • Generate fusions with split reporter fragments (BiFC, NanoBiT, etc.)

    • Co-express in mammalian cells

    • Measure reconstituted reporter activity

    • Visualize interaction by microscopy or quantify by luminescence

  • Advantages: Can visualize interactions in cellular context; good for confirming interactions

  • Technical Considerations: Optimize linker lengths; irreversible complementation for some systems

• Hydrogen-Deuterium Exchange Mass Spectrometry (HDX-MS):

  • Methodology:

    • Analyze protein alone and in complex with binding partners

    • Identify regions with altered deuterium uptake upon complex formation

    • Map interaction interfaces at peptide resolution

  • Advantages: Maps interaction interfaces; works with large complexes

  • Technical Considerations: Requires significant amounts of purified protein

These methodological approaches provide complementary information about interaction partners, binding affinities, and the structural basis of protein-protein interactions involving the Early 31 kDa protein .

How can recombinant adenoviral proteins be used to develop improved diagnostic tools for adenovirus infections?

Recombinant adenoviral proteins, including the Early 31 kDa protein, offer significant potential for developing advanced diagnostic tools:

• Serological Assay Development:

  • Methodological Approach:

    • Use purified recombinant proteins as antigens in ELISA or multiplex bead assays

    • Develop assays that distinguish between serotype-specific antibody responses

    • Implement standardized protocols for clinical laboratory adoption

  • Advantages: Improved specificity over whole virus assays; ability to distinguish between serotypes

  • Applications: Seroprevalence studies, vaccine response monitoring, epidemiological surveillance

• Multiplex Detection Systems:

  • Methodological Approach:

    • Develop protein arrays with multiple adenoviral antigens

    • Implement Luminex or similar bead-based multiplex platforms

    • Design algorithms for interpreting complex antibody profiles

  • Advantages: Simultaneous detection of multiple serotype-specific responses; reduced sample volume requirements

  • Applications: Comprehensive serological profiling, detection of co-infections

• Point-of-Care Diagnostic Development:

  • Methodological Approach:

    • Engineer lateral flow immunoassays using recombinant viral proteins

    • Develop rapid antigen detection systems

    • Optimize for sensitivity and specificity in clinical specimens

  • Advantages: Rapid results without laboratory infrastructure; field applicability

  • Applications: Acute infection diagnosis, outbreak investigation, resource-limited settings

• Molecular Diagnostics Enhancement:

  • Methodological Approach:

    • Develop protein-based enrichment methods for viral particles

    • Create recombinant protein-based standards for quantitative PCR

    • Engineer aptamer-based detection systems using viral proteins as targets

  • Advantages: Improved sensitivity; standardized quantification

  • Applications: Enhanced molecular diagnostics, viral load determination

• Serotype-Specific Immunity Assessment:

  • Methodological Approach:

    • Develop assays using recombinant proteins from multiple serotypes

    • Implement neutralization assays using reporter systems

    • Create algorithms for predicting protective immunity

  • Advantages: Differentiation between serotype-specific responses; functional immunity assessment

  • Applications: Vaccine development, epidemiological studies, personalized medicine approaches