CoV-2 Envelope (1-75)
Description
Ion Channel Activity
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The TMD forms a cation-selective pore permeable to Na⁺, K⁺, and Ca²⁺, facilitating viral assembly and release .
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Phe20-Phe23 distortion enables semi-independent responses to pH and membrane composition, modulating ion flux .
Host Protein Interactions
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The CTD’s PDZ-binding motif recruits human PALS1, disrupting lung epithelial tight junctions and promoting viral spread (Fig. 2) . Cryo-EM shows the DLLV motif binds a hydrophobic pocket in PALS1’s PDZ-SH3 domain .
Immune Modulation
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E protein activates TLR2, triggering NF-κB and inflammasome pathways, but induces prolonged immune tolerance in monocytes .
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Tolerant monocytes exhibit reduced cytokine responses to secondary stimuli (e.g., LPS), contributing to sepsis risk in severe COVID-19 .
Comparative Analysis with Other Viroporins
| Feature | SARS-CoV-2 E | Influenza M2 | HIV Vpu |
|---|---|---|---|
| Pore hydration | Low (dehydrated) | High | Moderate |
| Helix tilt | ~10° | ~30° | ~20° |
| Pore diameter | 4–6 Å | 8–10 Å | 5–7 Å |
| Primary ions | Na⁺, K⁺, Ca²⁺ | H⁺ | Cl⁻ |
The E protein’s rigid, narrow pore and unique lipid interactions distinguish it from other viroporins .
Inhibitors and Binding Sites
Mutational studies (e.g., p.V25F with compensatory p.L27S) highlight the E protein’s structural plasticity and challenges in drug design .
Research Advancements
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Structural Dynamics: Full-length E protein in micelles exhibits a flexible linker between TMD and CTD, enabling dual functionality in ion transport and protein recruitment .
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Pathogenic Mutations: Deletion of E protein reduces viral titers by 20–100×, confirming its role in virion assembly .
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Immune Evasion: TLR2-mediated tolerance mechanisms explain prolonged immunosuppression in severe COVID-19 .
Challenges and Future Directions
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Drug Resistance: Compensatory mutations (e.g., L27S) restore ion channel activity in E protein mutants, complicating inhibitor development .
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Structural Heterogeneity: The CTD’s conformational flexibility necessitates advanced techniques (e.g., cryo-EM with cellular mimics) to capture functional states .
Product Specs
The 2019 novel coronavirus (2019-nCoV), a human-infecting coronavirus responsible for causing viral pneumonia, was first identified in December 2019 in a fish market located in Wuhan, Hubei province, China.
Genetic analysis reveals that 2019-nCoV shares 87% of its identity with the bat-derived severe acute respiratory syndrome coronavirus 2018 (SARS-CoV-2), which was discovered in Zhoushan, eastern China. Despite some amino acid variations, the receptor-binding domain (RBD) structure of 2019-nCoV closely resembles that of 2018 SARS-CoV. This similarity suggests that 2019-nCoV may also target the angiotensin-converting enzyme 2 (ACE2) receptor protein in humans.
Bats are considered a likely natural reservoir for 2019-nCoV. However, researchers hypothesize that an intermediate animal host, potentially from those sold at the seafood market, played a role in transmitting the virus to humans. Notably, studies indicate that the 2019-nCoV genome is a product of recombination, particularly within the spike glycoprotein, involving a bat coronavirus and an unknown coronavirus.
This product consists of a recombinant protein derived from E. coli. It comprises the Envelope protein of the Coronavirus 2019 (CoV-2), specifically the Wuhan-Hu-1 strain, encompassing amino acids 1 to 75. The protein is fused with a GST-tag at the N-terminal and a His-tag at the C-terminal. Its calculated molecular weight is 36.8 kDa, and under reducing conditions, it migrates between 33-35 kDa on SDS-PAGE.
The CoV-2 Envelope protein is provided in a buffer solution containing 20mM Tris, 5mM EDTA, 0.5M Arginine at pH 8, and 10% sucrose.
The lyophilized CoV-2 Envelope protein remains stable at room temperature for up to 3 weeks. However, it is recommended to store it desiccated at a temperature below -18°C. Once reconstituted, the CoV2 Envelope protein should be stored at 4°C for 2-7 days. For long-term storage, it is advisable to store it below -18°C. To enhance stability during long-term storage, consider adding a carrier protein such as 0.1% HSA or BSA. Avoid repeated freeze-thaw cycles to maintain protein integrity.
To prepare a working stock solution, add deionized water to the lyophilized pellet to achieve a concentration of approximately 0.5mg/ml. Allow the pellet to dissolve completely before use.
Analysis by SDS-PAGE indicates that the protein purity is greater than 90%.
E.Coli
Purified by Metal-Afinity chromatographic technique.
Q&A
What is the structural composition of the SARS-CoV-2 envelope protein?
The SARS-CoV-2 envelope (E) protein is a 75-residue viroporin that forms a cation-selective channel across the ERGIC (Endoplasmic Reticulum-Golgi Intermediate Compartment) membrane . The protein contains a transmembrane (TM) domain that assembles into a pentameric ion channel . Structural analysis using nuclear magnetic resonance (NMR) has revealed that the TM domain forms a compact and rigid helical bundle with a helix distortion at residues Phe20–Phe23 . This structure differs significantly from equivalent viroporins of influenza and HIV-1 viruses in lipid bilayers, as the ETM helical bundle is more immobilized than M2 and Vpu helical bundles . The protein shows conformational plasticity that is likely sensitive to the membrane environment .
How does the lipid composition of the SARS-CoV-2 envelope differ from host cell membranes?
The lipid envelope of SARS-CoV-2 has a significantly different composition from host cell membranes, presenting potential targets for therapeutic intervention. Lipidomic analysis has revealed that the viral envelope comprises mainly phospholipids (PLs), with notably low levels of cholesterol and sphingolipids compared to host membranes . Unlike cellular membranes, procoagulant aminophospholipids (aPLs), such as phosphatidylethanolamine (PE) and phosphatidylserine (PS), are present on the external side of the viral envelope at levels exceeding those on activated platelets . This unique lipid profile results from the fact that coronaviruses bud from the endoplasmic reticulum (ER)/Golgi intermediate complex and exit via lysosomal secretion, rather than from the plasma membrane . The distinct lipid composition enables the viral particles to directly promote blood coagulation and potentially facilitate virion uptake via apoptotic cell mimicry .
What is the mutation rate of the SARS-CoV-2 envelope protein and what types of mutations have been identified?
The SARS-CoV-2 envelope protein is highly conserved with a mutation rate below 2%, making it one of the most stable proteins in the viral genome . In a study of 120 COVID-19 patients, 10 nucleotide changes were identified in the E gene, with 8 (80%) being silent mutations that do not alter the amino acid sequence . Only 2 (20%) missense mutations (amino acid altering) were found: L73F and S68F . These mutations are significant as they introduce new helix structures in the E protein mutants . The conservation of the E protein sequence across SARS-CoV-2 variants suggests its critical functional importance for viral replication and pathogenicity, making it a potential target for broad-spectrum antiviral development and diagnostics .
What methods are used to study the structure of the SARS-CoV-2 envelope protein?
Researchers employ several sophisticated techniques to determine the structure of the SARS-CoV-2 envelope protein:
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Nuclear Magnetic Resonance (NMR) Spectroscopy: This has been the primary method used to elucidate the molecular structure of the E protein . The process involves:
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Computational Modeling: Bioinformatics approaches are used to predict structural folding and map epitopes across the protein .
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Membrane Environment Comparison: Studies have examined structural differences between E protein in lipid bilayers versus micelle environments (such as LMPG and DPC micelles) . The bilayer-derived ETM structural model was calculated from 87 interhelical distance constraints, providing a more accurate representation than micelle-based models .
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Sequence Alignment Analysis: Comparative analysis of envelope sequences across different coronaviruses reveals areas of high sequence homology and structural conservation .
How does the SARS-CoV-2 envelope protein contribute to viral pathogenicity and host immune response?
The SARS-CoV-2 envelope protein plays multifaceted roles in viral pathogenicity and host immune responses. E protein mediates the budding and release of progeny viruses and activates the host inflammasome . In SARS-CoV-1, E protein deletion resulted in attenuated viruses, and mutations that abolished channel activity caused reduced virus pathogenicity, suggesting similar mechanisms in SARS-CoV-2 .
The protein's ion channel activity appears to be central to its pathogenic effects. This activity is blocked by compounds such as hexamethylene amiloride (HMA) and amantadine (AMT), which also inhibit viroporins of influenza A virus and HIV-1 . From an immunological perspective, immunoinformatic analysis has identified major immunogenic domains of the SARS-CoV-2 envelope protein that could be targeted for vaccine development .
Research has also revealed that mutations like S68F and L73F can significantly enhance the stability and binding affinity of protein E's C-terminal motif to the Protein Associated with LIN7 1, MAGUK P55 Family Member (PALS1) . This increased binding may promote local viral spread and infiltration of immune cells into lung alveolar spaces, potentially exacerbating disease severity .
What are the implications of the unique lipid composition of the SARS-CoV-2 envelope for therapeutic development?
The distinct lipid composition of the SARS-CoV-2 envelope presents novel opportunities for therapeutic intervention. The virus envelope's phospholipid-rich membrane with low cholesterol and sphingolipid content differs substantially from host cell membranes, potentially allowing for selective targeting without significant damage to host tissues . This selectivity is crucial for developing therapies with minimal side effects.
The presence of externalized aminophospholipids (aPLs) on the viral envelope, which contribute to coagulation activation, suggests potential mechanisms for addressing COVID-19-associated coagulopathy . In vitro studies have demonstrated that certain lipid-disrupting agents can effectively reduce viral infectivity. Specifically, oral rinses containing surfactant and polar components showed efficacy against SARS-CoV-2, with this effect confirmed in a randomized controlled clinical study in COVID-19 patients .
These findings indicate that lipid-targeting approaches represent an antiviral strategy that may be relatively resistant to viral mutation. As one study noted: "These studies demonstrate the accessibility and importance of lipids as a potential target for antiviral approaches, which is unlikely to be impacted by mutation of the virus" . This suggests that envelope-targeting therapeutics could maintain efficacy against emerging variants, addressing a critical challenge in COVID-19 treatment development.
How does the structure of the SARS-CoV-2 envelope protein compare with equivalent proteins in other viruses, and what are the functional implications?
The SARS-CoV-2 envelope protein structure exhibits both similarities and notable differences compared to equivalent proteins in other viruses, with significant functional implications:
Compared to influenza virus M2 and BM2 transmembrane domains:
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The SARS-CoV-2 ETM helical bundle is more compact and rigid
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Influenza viroporins have a higher percentage of polar residues (such as His and Ser)
Compared to HIV-1 Vpu transmembrane domain:
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Both have a high percentage of hydrophobic residues
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HIV-1 Vpu forms a shorter (~20 Å vertical length) pentameric helical bundle
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Vpu helices are more tilted (~20°) than SARS-CoV-2 E protein
Functionally, the SARS-CoV-2 E protein is more immobilized than M2 and Vpu helical bundles and does not undergo rigid-body fast uniaxial rotation at high temperatures . This immobilization suggests extensive interaction with lipids, which may influence the protein's ion channel properties and stability .
The helix distortion at residues Phe20–Phe23 is a unique feature that may cause the two halves of the protein to respond semi-independently to environmental factors such as pH, charge, membrane composition, and interactions with other viral and host proteins . This conformational flexibility could be linked to the protein's multiple functions in viral assembly, budding, and pathogenicity.
What experimental approaches are most effective for studying SARS-CoV-2 envelope protein mutations and their functional effects?
Research on SARS-CoV-2 envelope protein mutations requires a multifaceted approach combining molecular, structural, and functional analyses:
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Genomic Sequencing and Mutation Identification:
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Structural Analysis of Mutations:
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Functional Assessment:
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Comparative Analysis:
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In Vivo Assessment:
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Animal models can evaluate how specific mutations affect viral pathogenicity and immune responses
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These studies are critical for understanding the clinical significance of E protein mutations
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This comprehensive approach enables researchers to connect structural changes to functional outcomes and potential clinical implications of envelope protein mutations.
What is known about the immunogenic properties of the SARS-CoV-2 envelope protein and its potential as a vaccine target?
The SARS-CoV-2 envelope protein exhibits significant immunogenic properties that make it a potential vaccine target, though with important considerations:
Immunoinformatic analysis has successfully identified major immunogenic domains of the SARS-CoV-2 envelope protein . Researchers have mapped these domains among homologous proteins of coronaviruses with tropism for animal species that are closely interrelated with humans worldwide . This mapping revealed high sequence homology for some virus specimens, while structural mapping of epitopes showed interesting maintenance of structural folding and epitope sequence localization even in envelope proteins with lower alignment scores .
The highly conserved nature of the envelope protein (mutation rate <2%) is advantageous for vaccine development, as it suggests that immune responses targeting this protein might be effective against multiple variants . Following the One-Health approach, evidence provides a molecular structural rationale for a potential role of taxonomically related coronaviruses in conferring protection from SARS-CoV-2 infection .
Mutations in the envelope protein can potentially alter its immunogenic properties. The S68F and L73F mutations identified in clinical samples introduce new helix structures in the E protein mutants, which could impact immunogenicity . Molecular docking studies indicated that these mutations could enhance the stability and binding affinity of protein E's C-terminal motif to host proteins, potentially affecting viral pathogenicity .
For vaccine development targeting the E protein, both B-cell and T-cell epitopes should be considered, with emphasis on conserved regions that maintain structural integrity across variants. Targeting the ion channel function specifically might provide an alternative approach for vaccine-induced immunity against SARS-CoV-2.
How can the SARS-CoV-2 envelope protein be targeted for antiviral development, and what are the most promising approaches?
The SARS-CoV-2 envelope protein presents multiple targetable features for antiviral development:
The most promising approaches likely involve targeting the unique aspects of the E protein that differentiate it from host proteins, such as its ion channel function and distinctive lipid environment, while accounting for potential resistance mechanisms through combination therapies or targeting highly conserved regions.
Product Science Overview
The Coronavirus 2019 Envelope (E) protein, specifically the recombinant form encompassing amino acids 1-75, plays a crucial role in the life cycle of the virus. This protein is integral to the structure and function of the virus, contributing to its assembly, budding, and pathogenesis.
The E protein is a small, integral membrane protein that is involved in several critical aspects of the virus’s life cycle. It is known for its role in:
- Assembly: The E protein aids in the assembly of the virus particles.
- Budding: It is involved in the budding process, where new viral particles exit the host cell.
- Envelope Formation: The protein contributes to the formation of the viral envelope, which is essential for the virus’s infectivity.
- Pathogenesis: The E protein is also implicated in the pathogenesis of the virus, influencing its ability to cause disease .
Recent studies have expanded our understanding of the E protein’s structural motifs and topology. It functions as an ion-channelling viroporin, interacting with other coronavirus proteins and host cell proteins . For instance, the palmitoylation of the SARS-CoV-2 E protein at specific cysteine residues is crucial for its stability and interaction with other structural proteins, which is vital for the production of virus-like particles .
