Recombinant Hepatitis B virus genotype G Large envelope protein (S)
Description
Introduction to HBV Envelope Proteins
Hepatitis B virus encodes three envelope proteins that form the viral surface: large (L), middle (M), and small (S). These proteins are essential for viral assembly, infectivity, and host interactions. The large envelope protein, which is the focus of this report, is translated from 2.4-kb RNA and is detected in Western blotting as p39 (unglycosylated form) and gp42 (glycosylated form) . These envelope proteins share the same C-terminal S-domain but differ in their N-terminal extensions.
The L protein contains three domains: pre-S1 (N-terminal), pre-S2 (middle), and S (C-terminal). Research has demonstrated that the pre-S1 domain is particularly critical for viral infectivity and host cell receptor binding. Studies investigating the hepatitis delta virus (HDV), which utilizes HBV envelope proteins for its infectious cycle, have shown that only particles containing all three envelope proteins (S, M, and L) demonstrate infectivity, with the L protein being essential for this process .
The specific structure and functionality of these envelope proteins vary across the ten recognized HBV genotypes (A through J), each with distinct geographical distributions and clinical implications. The genotype G Large envelope protein exhibits unique characteristics that contribute to its specific virological properties.
Structure and Expression
The Large envelope protein consists of approximately 400 amino acids, with the recombinant form of genotype G Large envelope protein spanning amino acids 2-399 . When expressed recombinantly with N-terminal His-tags in systems like E. coli, the protein can be purified through affinity chromatography techniques for research applications.
The expression of the Large envelope protein is regulated by Surface promoter I (SPI), which controls the transcription of the 2.4-kb mRNA. Interestingly, different HBV genotypes show variations in promoter activity, which affects protein expression levels . These differences in expression regulation contribute to the distinct virological characteristics observed across genotypes.
Recombination Patterns
Genotype G frequently participates in intergenotypic recombination events, creating complex variants with mixed genetic characteristics. A notable example is the A/C/G intergenotypic recombinant identified in patients with chronic HBV infection in southern China . Phylogenetic analysis based on the S gene initially suggested this recombinant to be genotype G, but extended genotyping using the complete genome revealed it to be an A/C/G intergenotype more closely related to genotype C .
Breakpoint analysis demonstrated that this recombinant contained a complex arrangement of genomic fragments from genotypes A, G, A, and C . Interestingly, while typical genotype G strains are often associated with HBeAg-negative status, patients infected with this A/C/G recombinant were HBeAg-positive and demonstrated high viral loads, indicating competent viral replication capacity .
Comparative Analysis with Other Genotypes
Sequence analysis reveals significant variability across HBV genotypes, with divergence ranging from 6% to 15% in regulatory regions like the Core promoter . These genetic differences translate to functional variations in viral replication, protein expression, and secretion patterns.
Different genotypes exhibit varying preferences for viral lifecycle strategies. For example, genotypes B2 and F1b appear to favor the recycling of viral particles back to the nucleus to increase the cccDNA pool, while genotypes A2 and C1 seem to prioritize the secretion of viral particles . These strategic differences may influence disease progression and response to antiviral therapies.
Functional Properties of the Large Envelope Protein
The Large envelope protein plays critical roles in the HBV lifecycle, particularly in viral assembly and entry into host cells. Understanding these functions is essential for developing targeted interventions against HBV infection.
Role in Viral Infectivity
Research examining HDV, which requires HBV envelope proteins for its infectious cycle, has provided valuable insights into the function of the Large envelope protein. Studies have demonstrated that only HDV particles coated with all three envelope proteins (S, M, and L) showed evidence of infectivity in experimental systems .
More specifically, the pre-S1 domain of the L protein has been identified as critical for infectivity. Particles lacking the L protein or containing only S and M proteins failed to demonstrate infectious capacity, indicating that the M protein, despite containing a binding site for polymerized albumin in its pre-S2 domain, is insufficient for initiating infection .
Effect of Mutations on Protein Function
Mutations in the pre-S1 region can significantly alter the expression and function of the Large envelope protein. Experimental studies have shown that certain point mutations that prevent L protein expression can result in the production of a P-L fusion protein (p41/gp44) instead of the normal p39/gp42 forms .
The effect of mutations varies depending on their specific location. For instance, the Q3* nonsense mutation in genotype D and the G23* mutation in genotype A led to the production of p41/p44 doublets, while the W52* mutation in genotype A and K38* mutation in genotype D eliminated this production entirely . These findings highlight the complex relationship between genetic alterations and protein function, which can influence viral pathogenesis and disease outcomes.
Recombinant Production Systems
The production of recombinant HBV envelope proteins provides valuable tools for research, diagnostics, and potential therapeutic applications. Various expression systems and purification techniques have been employed to obtain functional recombinant proteins.
Expression in E. coli
One common approach for producing recombinant HBV genotype G Large envelope protein involves expression in E. coli systems. The protein can be engineered with fusion tags, such as N-terminal His-tags, to facilitate purification and detection . The availability of the recombinant protein (Q9IBI3) spanning amino acids 2-399 demonstrates the feasibility of this approach .
Purification Methods and Quality Control
Purification of His-tagged recombinant proteins typically employs affinity chromatography with nickel or cobalt resins, followed by additional purification steps as needed. Quality control measures often include SDS-PAGE analysis, Western blotting with specific antibodies, and mass spectrometry to confirm protein identity and purity.
The purified recombinant proteins can then be characterized for their structural integrity and functional properties through various biochemical and biophysical techniques. These analyses provide insights into the protein's behavior and potential applications in research and clinical settings.
Applications in Research and Diagnostics
Recombinant HBV genotype G Large envelope protein has numerous applications across basic research, diagnostics, and therapeutic development.
Studies of Viral Entry Mechanisms
The recombinant Large envelope protein serves as a valuable tool for studying the mechanisms of HBV entry into host cells. Research has established that the pre-S1 domain is crucial for viral infectivity, making it an important target for mechanistic studies . By investigating the interactions between the recombinant protein and cellular receptors, researchers can gain insights into the molecular details of viral attachment and entry.
These studies contribute to our understanding of host-virus interactions and may reveal potential targets for antiviral interventions. The availability of recombinant proteins from different genotypes, including genotype G, enables comparative analyses that can highlight genotype-specific aspects of the infection process.
Development of Diagnostic Assays
Recombinant viral proteins are widely used in developing serological assays for detecting antibodies against HBV in patient samples. The genotype G Large envelope protein, with its unique characteristics, may offer advantages in developing diagnostic tests that can distinguish between different HBV genotypes or identify specific recombinant strains.
Such diagnostics could provide more detailed information about the infecting virus, potentially guiding treatment decisions and improving patient management. The high purity and defined composition of recombinant proteins make them ideal reagents for these applications.
Comparative Virological Properties
Different HBV genotypes exhibit distinct virological characteristics, including variations in replication efficiency, antigen expression, and secretion patterns. These differences contribute to genotype-specific disease profiles and treatment responses.
Replication and Secretion Patterns
Studies comparing different HBV genotypes have revealed interesting differences in their replication strategies. While genotypes A2 and C1 showed lower levels of cccDNA, pgRNA, and intracellular HBV DNA compared to genotypes B2 and F1b, similar levels of extracellular DNA were observed across all genotypes .
This paradoxical finding suggests that genotypes with lower replication capacity, like genotype C, may compensate with more efficient virion secretion, potentially leading to rapid viral spread without eliciting a strong immune response . Such a strategy could contribute to the establishment of persistent infections, influencing disease progression and clinical outcomes.
Antigen Expression and Secretion
The expression and secretion of viral antigens also vary significantly across genotypes. For instance, genotype C1 demonstrated the highest levels of HBeAg expression and secretion, despite its relatively low replication rate . Conversely, genotypes D1 and F1b showed the lowest levels of HBeAg.
Interestingly, the relationship between mRNA levels and protein expression is not always straightforward. While genotypes A2 and D1 had higher levels of Precore mRNA, this did not directly correlate with HBeAg expression, suggesting that post-translational factors also influence antigen production and secretion .
Genotype A2 showed a unique pattern of retaining approximately 50% of expressed HBeAg intracellularly, which may contribute to immune modulation and viral persistence . The intracellular retention of HBeAg has been associated with suppression of immune responses, providing a mechanism that favors chronic infection.
Clinical Implications of Genotype G Infections
The unique characteristics of HBV genotype G and its recombinants have important implications for clinical outcomes and patient management. Understanding these implications is essential for developing effective strategies for prevention, diagnosis, and treatment.
Virological Features of Genotype G Recombinants
The A/C/G intergenotypic recombinant identified in southern China displayed virological features distinct from typical genotype G strains . Unlike pure genotype G infections, which are often associated with HBeAg-negative status, patients infected with this recombinant were HBeAg-positive and maintained high viral loads (>2×106 IU/ml) .
Analysis of viral replication capacity demonstrated that these recombinant strains had competent replication similar to genotypes B and C . This finding highlights the impact of recombination on viral behavior and suggests that recombinant strains may exhibit characteristics different from either parental genotype.
Implications for Disease Management
The altered virological properties of genotype G recombinants may influence disease progression and response to antiviral therapies. The presence of competent replication in recombinant strains suggests they may cause persistent infections with potentially different clinical courses compared to pure genotype infections.
Understanding the characteristics of these recombinant viruses is crucial for developing effective diagnostic tools and treatment strategies. The high similarity between recombinants found in different Asian countries (e.g., 98-99% similarity between the Guilin and Vietnam recombinants) suggests potential transmission routes and epidemiological connections that warrant further investigation .
Product Specs
Note: We prioritize shipping the format currently in stock. However, if you have specific format requirements, please indicate them when placing your order and we will accommodate your request.
Note: All of our proteins are shipped with standard blue ice packs by default. If dry ice shipping is required, please communicate with us in advance, as additional fees will apply.
Generally, the shelf life of the liquid form is 6 months at -20°C/-80°C. The shelf life of the lyophilized form is 12 months at -20°C/-80°C.
Target Background
Q&A
Basic Research Questions
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How does Hepatitis B virus genotype G differ from other HBV genotypes in terms of its envelope proteins?
HBV genotype G has several distinctive characteristics compared to other genotypes:
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It contains a 36 bp insertion in the core gene, which affects viral replication
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It has mutations preventing HBeAg expression
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It typically requires coinfection with another HBV genotype (primarily HBV/A) for effective replication
Studies have shown that HBV/G infections occur predominantly in males (92%) and are primarily associated with male homosexual sex (67%). All patients with HBV/G are typically infected with HBV/A or recombinant HBV/A/G strains . Canadian HBV/G strains display increased sequence divergence (1.57±0.62%) compared to other known HBV/G sequences .
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What post-translational modifications occur in Hepatitis B virus genotype G Large envelope protein?
The HBV envelope proteins undergo several post-translational modifications:
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N-linked glycosylation: All three envelope proteins have a potential N-glycosylation site at N146 of the S domain. LHBs exists in two forms due to glycosylation: p39 (non-glycosylated) and gp42 (glycosylated)
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N-terminal myristoylation: The N-terminus is myristoylated at glycine 2, which is essential for infection
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O-linked glycosylation: HBV genotypes C and D have an O-linked glycosylation site at T34 of the preS2 domain, though this may differ in genotype G
Interestingly, only approximately 50% of HBV envelope proteins bear N146-linked glycans. This coexistence of nonglycosylated and glycosylated N146 at the surface of HBV appears to reflect the dual function of this determinant in infectivity and immune escape .
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What expression systems are commonly used for producing Recombinant Hepatitis B virus genotype G Large envelope protein?
Several expression systems have been documented for producing recombinant HBV envelope proteins:
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E. coli: Used for producing non-glycosylated forms, particularly for structural studies
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HEK293 cells: Human cell lines provide proper post-translational modifications including glycosylation
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Recombinant adenoviral vectors: Enable expression of large envelope proteins in various cell types
For experimental purposes, researchers should select an expression system based on their specific requirements. If glycosylation patterns are critical, mammalian expression systems are preferred. For high yield of non-glycosylated protein, bacterial systems may be more suitable .
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Advanced Research Applications
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What methodologies can be used to study the interaction between Hepatitis B virus genotype G Large envelope protein and viral core proteins?
Several methodological approaches have been documented:
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Co-immunoprecipitation: Used to study direct protein-protein interactions between envelope and core proteins. This method identified several core amino acids essential for direct interaction with L proteins, including residue Y132 (crucial for capsid formation) and residues L60, L95, K96, and I126
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Confocal microscopy: Enables visualization of protein colocalization in cellular contexts. Studies have shown that L protein constitutes a molecular platform for recruiting S and core proteins in a perinuclear environment
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Mutagenesis studies: Site-directed mutagenesis of the translation initiation codon ATG of each envelope protein has revealed that mutant genomes unable to produce one or two of these proteins cannot form Dane particles (infectious HBV virions)
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Pulse-chase experiments: Used to track protein synthesis, interaction, and degradation over time. Metabolic labeling with [35S]Cys followed by immunoprecipitation can monitor the dynamics of envelope protein interactions
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How does coinfection of HBV genotype G with genotype A affect the functionality of the Large envelope protein?
HBV/G typically requires coinfection with HBV/A for effective replication and viral production. The dynamics of this relationship include:
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Coinfecting genotypic prevalence fluctuates over time, with periods of HBV/G monoinfection in some patients
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Novel Ae/G recombinants have been identified in Japanese HIV-1-positive men who have sex with men (MSM). These recombinants were found to be coinfected with HBV/Ae in a recombinant-dominant fashion
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The core gene of recombinant strains shows high sequence similarity to HBV/G
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No major drug-resistant mutations have been found in newly identified HBV Ae/G recombinants
This complex relationship suggests that envelope proteins from both genotypes may complement each other's functions, potentially through structural contributions or interaction with host factors .
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What experimental approaches can be employed to analyze the role of HBV genotype G Large envelope protein in viral assembly?
Several experimental techniques have proven valuable:
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Transient transfection systems: Producing mutant or wild-type L, S, or core proteins separately or in combination in Huh7 cells allows analysis of protein interactions required for virion formation
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Immunoblotting analysis: Detection of HBV envelope proteins can be achieved using monoclonal antibodies (such as H166) or polyclonal antibodies (such as R247)
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PNGase F treatment: This enzyme removes N-linked glycans, allowing distinction between glycosylated and non-glycosylated forms of envelope proteins
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Virion production assays: Measurement of HDV RNA by Northern blotting or HBV DNA by Southern blotting after anti-pre-S1 antibody immunoprecipitation can quantify successful virion assembly
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Cell fractionation: Separating cytoplasmic fractions from membrane fractions helps determine the localization and trafficking of envelope proteins
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What are the structural determinants in HBV genotype G Large envelope protein that contribute to viral infectivity?
Several structural elements have been identified as crucial for infectivity:
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PreS1 domain: Critical for binding to the hepatocyte receptor sodium taurocholate cotransporting polypeptide (NTCP)
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N-terminal myristoylation: Essential for infection, likely by facilitating membrane interactions
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"a" determinant: An antigenic domain in the S region that is exposed on the outside of the envelope and serves as a major target for neutralizing antibodies
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Transmembrane domains: The S domain contains four transmembrane domains that are essential for proper protein folding and envelope formation
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Cytosolic loops: Studies have identified cytosolic loops I and II (CYL-I and CYL-II) as important for viral assembly. Specifically, tryptophan residues at positions 196, 199, and 201 in CYL-II exert a matrix function for assembly
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How can structure-guided approaches be used to develop inhibitors targeting HBV genotype G Large envelope protein?
Structure-guided drug discovery approaches include:
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Virtual high-throughput screening: After modeling the three-dimensional structure of LHBs, virtual screening against compound databases can identify potential inhibitors. One study using the ZINC database identified four compounds (ZINC11882026, ZINC19741044, ZINC00653293, and ZINC15000762) showing appreciable binding affinity with LHBs protein
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Targeting key interaction residues: Focusing on residues essential for direct interaction between core and L proteins (Y132, L60, L95, K96, and I126) could yield effective inhibitors of viral assembly
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Rational design targeting PreS domains: The PreS1 and PreS2 domains of LHBs play crucial roles in viral morphogenesis, infection, and propagation, making them promising targets for antivirals
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Modifying glycosylation patterns: Since alterations in glycosylation affect both virion assembly and immune escape, compounds that interfere with specific glycosylation events could serve as effective antivirals
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What methodological challenges exist in studying HBV genotype G envelope proteins, and how can they be addressed?
Several methodological challenges and their potential solutions include:
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Coinfection complexity: HBV/G typically coinfects with HBV/A, making it difficult to study G-specific properties. Solution: Use of recombinant systems expressing only genotype G proteins, or carefully designed deconvolution experiments
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Low prevalence: HBV/G is rare worldwide, limiting sample availability. Solution: Development of robust recombinant expression systems and molecular clones
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Lack of structural data: The complete structure of LHBs has not been fully elucidated. Solution: Computational modeling combined with experimental validation using techniques like cryo-electron microscopy
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Post-translational modifications: The complex glycosylation patterns of envelope proteins are difficult to recapitulate in vitro. Solution: Use of mammalian expression systems like HEK293 cells instead of bacterial systems when studying glycosylated forms
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Functional assays: Testing infectivity requires specialized cell lines permissive to HBV infection. Solution: Use of HepaRG cells or primary human hepatocytes for in vitro infection assays
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How does Hepatitis B virus genotype G Large envelope protein interact with the host immune system?
Research into immune interactions reveals:
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The "a" determinant in the S domain is a major target of neutralizing antibodies, making it critical for both vaccine development and viral immune escape
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The coexistence of glycosylated and non-glycosylated forms of the envelope proteins at position N146 appears to reflect a dual function in infectivity and immune escape
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Subviral particles (SVPs) containing L/M/SHBs are released in large amounts from infected hepatocytes and may facilitate escape from the immune system
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Therapeutic approaches targeting immune responses include:
Understanding these interactions provides the foundation for developing more effective immunotherapeutic strategies against chronic HBV infection.
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What recombinant forms of HBV genotype G have been identified, and what are their implications for research?
Several recombinant forms have been documented:
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Novel Ae/G recombinants identified in Japanese HIV-1-positive MSM, where the core gene had high sequence similarity to HBV/G
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HBV A/G recombinants in Canadian HIV-1-positive individuals, showing increased sequence divergence (1.57±0.62%) compared to previously described HBV/G sequences
Research implications include:
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These recombinants may represent adaptation mechanisms that enhance viral fitness during coinfection
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They provide natural tools for studying which domains of HBV/G envelope proteins are functionally critical
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The association with HIV-1 coinfection suggests potential interactions between these viruses that warrant further investigation
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The pathogenicity of novel HBV Ae/G recombinants requires longitudinal studies, especially in HIV-1-positive individuals
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