Recombinant Human adenovirus B serotype 3 Early E3B 14.5 kDa protein
Description
Primary Structure and Domains
The E3B 14.5 kDa protein contains an N-terminal signal sequence that directs its insertion into cellular membranes. For the related adenovirus type 5 protein, this signal sequence undergoes cleavage predominantly between Cys-18 and Ser-19 during protein maturation . The C-terminal two-thirds of the protein exhibits a highly structured region predicted to consist of five β-strands and one α-helix, which is crucial for maintaining the protein's functional integrity . This region appears to be responsible for binding to putative cellular receptors, mediating the protein's immunomodulatory effects . The mature protein adopts a type I bitopic membrane orientation, with its N-terminus positioned in the lumen and C-terminus in the cytoplasm .
Oligomeric State and Stability
Studies on the E3-14.7K protein from adenovirus type 5 have demonstrated that it exists as a stable high-order oligomeric structure in solution, specifically as a nonamer . This oligomerization may contribute significantly to its functional properties and stability. Such structural arrangement suggests a complex mechanism of action that might involve multiple interaction sites for host cellular proteins, potentially enhancing its immunomodulatory efficacy .
Metal Binding Properties
The E3-14.7K protein demonstrates metal binding capabilities that appear essential for its biological activity. Research has shown that cysteine/serine mutants lacking these metal binding properties also lack in vivo antiapoptotic activity, suggesting a critical role for metal coordination in the protein's function . This characteristic likely extends to the serotype 3 E3B 14.5 kDa protein given the high conservation of functional domains across adenovirus serotypes.
Functional Mechanisms and Cellular Interactions
The E3B 14.5 kDa protein plays crucial roles in viral defense against host immune responses, primarily through interactions with specific cellular pathways.
Inhibition of Apoptosis
Similar to its homologs, the E3B 14.5 kDa protein likely functions as an inhibitor of programmed cell death (apoptosis). The adenovirus E3-14.7K protein has been identified as an inhibitor of cell death mediated by tumor necrosis factor (TNF) and FasL receptor pathways . This antiapoptotic activity serves to protect virus-infected cells from premature destruction, allowing completion of the viral replication cycle .
Receptor Downregulation
In conjunction with another adenoviral protein (E3 10.4K), the E3 14.5 kDa protein forms a functional complex that downregulates the epidermal growth factor receptor (EGFR) in infected cells . This downregulation represents a sophisticated viral strategy to modulate host cell signaling pathways that might otherwise contribute to antiviral responses. The protein complexes operate within cytoplasmic membranes, which serve as the primary site of action for these immunomodulatory functions .
Prevention of TNF-Mediated Cytolysis
The E3 14.5 kDa protein, working in concert with E3 10.4K, prevents cytolysis by tumor necrosis factor in most cell lines . This protective effect is particularly important for virus-infected cells expressing adenovirus E1A proteins, which otherwise become susceptible to TNF-mediated killing . The protein has been characterized as a general inhibitor of TNF-mediated cytolysis, highlighting its broad protective capabilities against host immune defenses .
Expression and Recombinant Production
The recombinant form of Human adenovirus B serotype 3 Early E3B 14.5 kDa protein is produced using advanced biotechnological approaches to ensure structural and functional fidelity to the native viral protein.
Expression Systems
While specific expression systems for the serotype 3 protein are not detailed in the search results, research on similar adenoviral proteins indicates challenging aspects of recombinant production. For the E3-14.7K protein from adenovirus type 5, fusion to maltose-binding protein (MBP) proved most effective at generating soluble protein for biophysical characterization . This approach might similarly be employed for producing the recombinant serotype 3 variant.
Comparative Analysis with Other Adenoviral Proteins
The E3B 14.5 kDa protein exists within a broader context of adenoviral immunomodulatory proteins that collectively represent a sophisticated viral strategy for immune evasion.
Conservation Across Serotypes
The E3 14.5-14.7K proteins are highly conserved across multiple adenovirus serotypes, indicating their fundamental importance to adenoviral biology . This conservation suggests selective pressure to maintain these proteins' structures and functions throughout adenoviral evolution, likely due to their critical roles in counteracting host immune responses .
Functional Relationships with Other E3 Proteins
The E3B 14.5 kDa protein functions cooperatively with other adenoviral proteins, particularly E3 10.4K. Together, these proteins form a complex that mediates downregulation of cell surface receptors and prevents TNF-mediated cytolysis . This functional interdependence illustrates the integrated nature of adenoviral immune evasion mechanisms, with multiple viral proteins working in concert to subvert host defenses.
Research Applications and Significance
The recombinant E3B 14.5 kDa protein represents a valuable tool for various research applications in virology, immunology, and biotechnology.
Study of Viral Immune Evasion
This protein serves as a model for understanding how viruses evade host immune responses. Its ability to inhibit TNF-mediated cell death and modulate cellular receptor expression provides insights into sophisticated viral strategies for persistence within host organisms . Research using this recombinant protein can illuminate fundamental aspects of virus-host interactions.
Technical Considerations for Research Applications
When working with Recombinant Human adenovirus B serotype 3 Early E3B 14.5 kDa protein, several technical considerations affect experimental outcomes and interpretation.
Protein Solubility and Handling
Based on research with similar proteins, maintaining solubility can present challenges during recombinant expression and experimental handling. The use of fusion partners (such as MBP) has proven effective for increasing solubility while preserving functional properties . Appropriate buffer conditions and storage protocols are essential for maintaining protein integrity during experimental procedures.
Functional Assays
Assessing the biological activity of the E3B 14.5 kDa protein typically involves specialized assays for measuring anti-apoptotic effects, receptor downregulation, or protection from TNF-mediated cytolysis . These functional assays require careful design and appropriate cellular models to accurately reflect the protein's physiological activities.
Future Research Directions
Several promising avenues exist for advancing our understanding of the Recombinant Human adenovirus B serotype 3 Early E3B 14.5 kDa protein and its potential applications.
Serotype-Specific Properties
While much is known about E3 14.5-14.7K proteins generally, specific investigations of serotype 3 variants would help clarify potential functional differences between adenovirus groups. Such research could reveal unique properties that might be exploited for biotechnological or therapeutic purposes.
Host Interaction Partners
Comprehensive identification and characterization of cellular proteins that interact with the E3B 14.5 kDa protein would illuminate its mechanisms of action in greater detail. Proteomics approaches and interaction mapping could reveal previously unrecognized pathways through which this viral protein modulates host cellular functions .
Product Specs
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Target Background
Q&A
What is the structural composition of the adenovirus B serotype 3 early E3B 14.5 kDa protein?
The adenovirus B serotype 3 early E3B 14.5 kDa protein is encoded by an open reading frame in the E3 transcription unit. The full-length mature protein spans amino acids 22-134, with its initiation codon positioned 16 codons into the upstream 12.5K gene and its stop codon located seven codons into the downstream gp19K gene . The C-terminal region of this protein exhibits limited homology to the Ad2 and Ad5 6.7K protein, suggesting some conserved functional domains across different adenovirus subgroups . When expressed as a recombinant protein, it can be produced with a His-tag, maintaining its full-length structure when expressed in E.coli systems .
How is the adenovirus B serotype 3 early E3B 14.5 kDa protein detected in experimental settings?
Detection of the 14.5 kDa protein typically involves immunoprecipitation followed by SDS-PAGE analysis. Researchers have successfully developed specific antisera against this protein, which can be used to immunoprecipitate the protein from infected cells . For enhanced specificity, synthetic peptides representing residues 14 to 27 of the predicted protein have been used to generate rabbit antisera, which effectively immunoprecipitate the [35S]Cys-labeled protein from Ad3- or Ad7-infected cells . Western blot analysis following immunoprecipitation provides additional confirmation of protein identity and expression levels . When analyzing expression patterns, it's important to note that the Ad3 version migrates slightly faster than the Ad7 version during SDS-PAGE, despite their nearly identical sequences .
What is the relationship between adenovirus B serotype 3 early E3B 14.5 kDa protein and other E3 region proteins?
The E3B region of human adenoviruses codes for three highly conserved proteins: 10.4K, 14.5K, and 14.7K . The 14.5K protein functions in close association with the 10.4K protein, with which it forms a physical complex . This protein complex is functionally distinct from the 14.7K protein, as demonstrated through selective gene inactivation studies . Expression levels of these proteins can be affected by mutations in the E3 region, as deletions can profoundly alter splicing patterns, potentially increasing 10.4/14.5K expression while severely reducing expression of other E3 proteins, particularly E3/19K . Therefore, when designing experiments to study the 14.5K protein, researchers should carefully consider potential effects on the expression of neighboring genes.
What cellular localization pattern does the adenovirus B serotype 3 early E3B 14.5 kDa protein exhibit?
The adenovirus B serotype 3 early E3B 14.5 kDa protein has been characterized as a membrane protein that is synthesized during both early and late stages of viral infection . This membrane association is consistent with its functional role in modulating cell surface receptor expression. Subcellular fractionation studies and immunofluorescence microscopy can be employed to precisely determine its distribution pattern within infected cells. When designing experiments to analyze its localization, researchers should consider using membrane fraction isolation techniques and membrane protein-specific extraction buffers to ensure optimal recovery and detection of this protein.
What are the functional implications of the adenovirus E3/10.4K-14.5K protein complex in modulating host immune responses?
The E3/10.4K-14.5K protein complex plays a crucial role in viral immune evasion by down-regulating the apoptosis receptor CD95 (Fas, APO-1) on the cell surface . Transfection experiments have demonstrated that both proteins are required for this Fas suppression, as mutation of either gene restores Fas expression . This down-modulation of cell surface receptors represents a sophisticated viral strategy to prevent infected cells from undergoing apoptosis, thereby extending the window for viral replication. Methodologically, researchers investigating this function should employ flow cytometry to quantify cell surface receptor levels, combined with selective gene inactivation approaches to confirm the specific contribution of each protein component . Experimental designs should include appropriate controls with mutated versions of each protein (E3/10.4K*, E3/14.5K*, and E3/14.7K*) to distinguish their individual contributions to the observed phenotype.
What methodological approaches can be used to investigate the interaction between E3/10.4K and 14.5K proteins?
The physical interaction between E3/10.4K and 14.5K proteins can be investigated through several complementary approaches. Co-immunoprecipitation followed by Western blot analysis has been successfully employed to demonstrate this interaction . For more detailed characterization, researchers might consider:
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Proximity ligation assays to visualize protein interactions in situ
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Fluorescence resonance energy transfer (FRET) analysis with tagged protein variants
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Yeast two-hybrid or mammalian two-hybrid systems to map interaction domains
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Cross-linking studies followed by mass spectrometry to identify specific contact residues
When conducting these experiments, it is important to ensure that tagged versions of the proteins maintain their functional properties, as verified by their ability to down-regulate Fas expression. Control experiments should include mutations in key domains to identify regions essential for complex formation versus those required for effector functions.
How does the expression pattern of adenovirus B serotype 3 early E3B 14.5 kDa protein differ across infection stages?
The 14.5 kDa protein is synthesized at both early and late stages of infection , suggesting a temporal regulation that may correspond to different functional requirements during the viral life cycle. To investigate this expression pattern, researchers can employ a combination of:
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Time-course experiments with metabolic labeling ([35S]Cys or [35S]Met) followed by immunoprecipitation
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Real-time quantitative PCR to measure mRNA levels at different infection time points
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Western blot analysis of protein expression using specific antisera
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Pulse-chase experiments to determine protein turnover rates
Comparison of expression patterns between different adenovirus serotypes may provide insights into serotype-specific differences in pathogenesis. When designing such comparative studies, researchers should carefully control for variables such as multiplicity of infection, cell type, and detection sensitivity to ensure valid comparisons.
What is the comparative analysis of adenovirus B serotype 3 early E3B 14.5 kDa protein across different adenovirus subgroups?
Comparative analysis across adenovirus subgroups reveals important structural and functional differences. The C-terminal region of the adenovirus B serotype 3 early E3B 14.5 kDa protein has limited homology to that of the Ad2 and Ad5 6.7K protein . In contrast to subgroup B (Ad3 and Ad7), subgroup C adenoviruses (Ad2 and Ad5) have gaps of 409 and 367 bp, respectively, between the 12.5K and 6.7K genes . This region contains an open reading frame for a 14-kDa protein, although it lacks an initiation codon (ATG) . The potential protein encoded by this ORF shows homology to the N-terminal portion of the 16K protein with patchy homology elsewhere .
These differences may contribute to the distinct disease manifestations associated with different adenovirus subgroups. Methodologically, researchers investigating these differences should employ sequence alignment tools, structural prediction software, and functional assays to correlate sequence variations with biological activities. Recombinant expression systems can be used to produce chimeric proteins, allowing the identification of domains responsible for subgroup-specific functions.
