Recombinant White clover mosaic virus Movement protein TGB2 (ORF3)
Description
Biochemical Properties
TGB2 demonstrates specific biochemical properties that are crucial for its function:
Research has demonstrated that TGB2 possesses RNA binding capabilities as shown in Northwestern gel blot experiments, suggesting its direct interaction with viral RNA during the movement process .
Expression Systems
The recombinant form of WClMV TGB2 has been successfully expressed in bacterial systems. The commercially available recombinant protein is typically produced in Escherichia coli with an N-terminal His-tag to facilitate purification . This expression system allows for efficient production of the protein for both research and commercial applications.
Subcellular Localization and Trafficking
One of the most significant aspects of TGB2 is its distinctive subcellular localization pattern. Fluorescently tagged TGB2 has been observed to:
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Initially associate with the endoplasmic reticulum (ER) network and membranes surrounding the nucleus
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Localize to motile granules that utilize the ER-actin network for intracellular movement
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Later in the expression cycle, incorporate into vesicular structures with sizes ranging from approximately 0.5 to 4 μm
These vesicular structures appear to be associated with the plasma membrane and often move by cytoplasmic streaming, frequently becoming closely associated with the nuclear envelope . Importantly, TGB2 can associate with these vesicular structures independently, without requiring other viral proteins .
Interaction with the Endocytic Pathway
A notable discovery is that TGB2-containing vesicles are labeled with FM4-64, a marker for plasma membrane internalization and components of the endocytic pathway . Furthermore, TGB2 colocalizes in vesicles with Ara7, a Rab5 ortholog that marks the early endosome . This evidence strongly suggests that TGB2 interacts with the endocytic pathway during viral movement.
Protein interaction analysis has revealed that recombinant TGB2 interacts with a tobacco protein belonging to the highly conserved RME-8 family of J-domain chaperones, which are essential for endocytic trafficking in organisms like Caenorhabditis elegans and Drosophila melanogaster . This interaction further reinforces the involvement of the endocytic pathway in viral intracellular movement.
Function in the TGB Transport Complex
The Triple Gene Block consists of three proteins (TGB1, TGB2, and TGB3) that work cooperatively to facilitate viral RNA movement. While TGB1 appears to function as the primary movement protein that directly interacts with viral RNA and travels between cells, TGB2 plays a distinct supporting role .
Studies with White clover mosaic virus have demonstrated that TGB2 is essential for cell-to-cell movement but does not itself move between cells . In experiments where TGB proteins were transiently expressed to complement defective genes in viral clones, TGB2 only facilitated movement of the defective virus to adjacent cells, unlike TGB1 which enabled movement across several cell layers .
Interaction with TGB3
TGB2 and TGB3 exhibit a coordinated relationship in subcellular targeting. Both proteins colocalize in motile granules that use the ER-actin network for intracellular movement . Interestingly, while TGB3 can accumulate at plasmodesmata (the intercellular channels that connect plant cells) in the absence of TGB2, TGB3 requires TGB2 to incorporate into vesicular structures .
This interaction was demonstrated in plants infected with Potato mop-top virus (PMTV), where fluorescently tagged TGB3 was incorporated into vesicles only in the presence of virus-expressed TGB2, indicating that TGB2 recruits TGB3 to these structures .
Model for TGB-Mediated Viral Movement
Based on the collective evidence, a model for how the TGB proteins facilitate viral movement can be proposed:
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TGB1 functions as the main movement protein that binds viral RNA to form a ribonucleoprotein complex with the viral coat protein
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TGB2 and TGB3 serve as membrane anchors that direct the ribonucleoprotein complex to plasmodesmata
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TGB2 associates with the ER and later with vesicular structures involved in the endocytic pathway
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TGB3 accumulates at plasmodesmata and is recruited to vesicles by TGB2
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Together, these proteins increase the size exclusion limit of plasmodesmata to allow passage of the viral ribonucleoprotein complex
This coordinated action enables the virus to move from cell to cell without requiring the transport of intact virions, particularly for Group 1 viruses like WClMV where coat protein is not required for cell-to-cell movement .
Applications in Research
The recombinant TGB2 protein has significant value in research applications:
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As a tool for studying viral movement mechanisms
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For investigating plant cell membrane biology and trafficking pathways
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In developing potential antiviral strategies targeting viral movement
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For exploring the interaction between viruses and the plant endocytic pathway
The availability of purified recombinant TGB2 enables researchers to conduct detailed biochemical and structural studies that would otherwise be challenging with native viral proteins .
Product Specs
Note: We prioritize shipping the format currently in stock. However, if you have specific format requirements, please indicate them in your order. We will accommodate your request whenever possible.
Note: All proteins are shipped with standard blue ice packs by default. If dry ice shipment is required, please communicate this 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
KEGG: vg:944399
Q&A
What is the structure and function of White clover mosaic virus Movement protein TGB2 (ORF3)?
White clover mosaic virus Movement protein TGB2 (ORF3), also known as Triple gene block 2 protein (TGBp2), is a 116 amino acid viral protein with the sequence MPLTPPPNPQKTYQIAILALGLVLLAFVLISDHSPKVGDHLHNLPFGGEYKDGTKSIKYF QRPNQHSLSKTLAKSHNTTIFLLILGLIVTLHGLHYFNNNRRVSSSLHCVLCQNKH . It functions as an integral membrane protein that plays a critical role in viral cell-to-cell movement.
TGB2 is part of the triple gene block that encodes three proteins required for viral movement. The current model suggests that TGB2 helps localize viral ribonucleoprotein (vRNP) movement complexes to the plasma membrane and plasmodesmata, facilitating viral spread between cells . Unlike some other viral movement proteins, WCMV TGB2 can bind RNA in a sequence non-specific manner but is not required for RNA replication .
Methodology for structural analysis: For researchers investigating TGB2 structure, a combination of X-ray crystallography, NMR spectroscopy, and predictive modeling based on amino acid sequence is recommended. The hydrophobic domains suggest membrane-spanning regions that can be analyzed through hydropathy plotting and transmembrane prediction algorithms.
How does TGB2 facilitate viral cell-to-cell movement?
TGB2 contains vesicle-targeting signals that enable association with components of the endocytic pathway . Research indicates that TGB2 and TGB3 co-localize in cellular membranes and mobile granules, utilizing the actin-ER network to facilitate movement to the cell periphery and plasmodesmata .
TGB2 can independently increase the size exclusion limit (SEL) of plasmodesmata, though there is no evidence it can traffic between cells by itself . This function is crucial for allowing larger viral complexes to move through the plasmodesmata channels.
Experimental approach: To study this function, researchers should consider using fluorescently tagged TGB2 (such as mRFP-TGB2) expressed in plant cells, followed by visualization with confocal microscopy. Complementation assays with movement-defective viral mutants can confirm functionality. For example, experiments have shown that mRFP-TGB2 fusion protein could complement a TGB2 deletion in PMTV reporter constructs, restoring cell-to-cell movement capabilities .
What expression systems are most effective for producing recombinant TGB2?
For producing recombinant WCMV TGB2, E. coli expression systems have proven effective . The protein can be expressed with an N-terminal His-tag for purification purposes. When designing expression constructs, researchers should account for the hydrophobic nature of TGB2 which may affect solubility.
Recommended methodology:
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Clone the full-length TGB2 sequence (amino acids 1-116) into a prokaryotic expression vector with an N-terminal His-tag
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Transform into E. coli expression strains (BL21 or similar)
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Induce expression with IPTG under optimized conditions
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Lyse cells and purify using immobilized metal affinity chromatography (IMAC)
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Conduct buffer exchange to remove imidazole
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Store as lyophilized powder or in solution with 50% glycerol at -20°C/-80°C
Buffer considerations: For storage and reconstitution, Tris/PBS-based buffer with 6% Trehalose, pH 8.0 has been successfully used . Aliquoting is necessary to avoid repeated freeze-thaw cycles.
What techniques can be used to study TGB2 interaction with cellular membranes?
As an integral membrane protein that associates with the endocytic pathway, TGB2's interaction with cellular membranes is crucial to its function.
Methodological approaches:
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Protein-lipid interaction assays: These can reveal TGB2's association with specific lipids, providing insight into membrane targeting mechanisms .
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Confocal microscopy with co-localization markers: Express fluorescently tagged TGB2 alongside markers for different cellular compartments (ER, Golgi, endosomes). For example, studies have used transgenic Nicotiana benthamiana plants expressing ER-targeted GFP (35S::mGFP5ER-HDEL) to visualize ER co-localization .
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Subcellular fractionation: Separate cellular components through differential centrifugation to determine TGB2 localization biochemically.
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Fluorescence recovery after photobleaching (FRAP): To study membrane dynamics of TGB2.
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Bimolecular fluorescence complementation (BiFC): To visualize protein-protein interactions within membrane compartments.
How can researchers investigate the role of TGB2 in viral RNA trafficking?
TGB2 binds RNA in a sequence non-specific manner , suggesting it plays a role in trafficking viral RNA. Studies of similar movement proteins indicate they form ribonucleoprotein complexes crucial for systemic virus movement.
Experimental design recommendations:
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RNA binding assays: Electrophoretic mobility shift assays (EMSA) using purified recombinant TGB2 and labeled viral RNA fragments.
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UV crosslinking: To identify direct RNA-protein interactions.
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RNA immunoprecipitation (RIP): Using antibodies against TGB2 to pull down associated viral RNA.
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Viral complementation studies: Engineer virus constructs with fluorescently tagged RNA and monitor movement in the presence of wild-type or mutated TGB2.
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Phase separation analysis: Based on findings with similar viral movement proteins, investigate whether TGB2 undergoes phase separation with viral RNA to form droplets or membraneless compartments . In vitro assays can be used to visualize droplet formation with fluorescently labeled components.
What approaches are effective for studying TGB2 association with chloroplasts?
Evidence suggests WCMV infection induces chloroplast abnormalities and that viral components including TGB2 may associate with chloroplasts, potentially as sites of virus replication and encapsidation .
Methodological approaches:
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Confocal microscopy: Using chloroplast autofluorescence and fluorescently tagged TGB2 to visualize co-localization.
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Chloroplast isolation: Purify chloroplasts from infected tissue and analyze by Western blotting for TGB2 presence.
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Immunogold electron microscopy: For ultrastructural localization of TGB2 in relation to chloroplasts.
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Chloroplast proteomics: Compare protein profiles of chloroplasts from healthy versus infected tissue.
| Technique | Application | Advantages | Limitations |
|---|---|---|---|
| Confocal microscopy | Real-time visualization | Non-destructive, allows temporal analysis | Limited resolution |
| Electron microscopy | Ultrastructural analysis | High resolution visualization | Complex sample preparation |
| Biochemical fractionation | Quantitative analysis | Allows multiple assays | Potential contamination |
| Proteomics | Interaction networks | Comprehensive analysis | Complex data interpretation |
How do mutations in TGB2 affect its function in viral movement?
Understanding structure-function relationships through mutational analysis provides valuable insights into TGB2 mechanisms.
Experimental approach:
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Site-directed mutagenesis: Target conserved motifs, membrane-spanning regions, or charged residues. Studies of similar movement proteins show that mutating basic residues (R/K-G) can block phase separation and prevent systemic virus movement, while mutating acidic residues (D/E-G) can affect nucleolar trafficking .
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Viral movement assays: Introduce mutations into full-length viral clones or movement-complementation systems.
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Complementation experiments: Test whether mutated TGB2 can rescue movement of TGB2-deficient virus constructs. For example, a similar experimental design showed that mRFP-TGB2 fusion protein could complement a TGB2 deletion in PMTV reporter constructs .
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Protein localization studies: Examine whether mutations alter TGB2 subcellular localization using fluorescent protein fusions.
What methods can determine if TGB2 undergoes phase separation similar to other viral movement proteins?
Recent research shows that some viral movement proteins undergo phase separation to form membraneless compartments that concentrate biomolecules, which is critical for their function . While not directly demonstrated for WCMV TGB2, this property could be investigated based on findings with similar proteins.
Recommended methodology:
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In vitro droplet formation assays: Mix purified TGB2 with RNA under various buffer conditions to visualize potential droplet formation.
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Fluorescence recovery after photobleaching (FRAP): To determine the fluid properties of TGB2 condensates.
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Mutation analysis: Based on studies of other viral movement proteins, charged residues often mediate electrostatic interactions critical for phase separation . Test whether altering these residues affects TGB2 function.
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Co-localization with phase separation markers: Examine whether TGB2 partitions into known membraneless compartments like stress granules, as observed with other viral movement proteins .
What are the optimal conditions for storing and handling recombinant TGB2?
Proper handling of recombinant TGB2 is crucial for experimental reproducibility.
Recommended storage protocol:
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Store lyophilized protein at -20°C/-80°C upon receipt
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For reconstitution, centrifuge the vial briefly before opening
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Reconstitute in deionized sterile water to 0.1-1.0 mg/mL
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Add glycerol to a final concentration of 50% for long-term storage
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Aliquot to avoid repeated freeze-thaw cycles
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For working stocks, store aliquots at 4°C for up to one week
Troubleshooting guidance: If protein activity decreases, check for:
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Repeated freeze-thaw cycles
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Improper pH of storage buffer
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Protein aggregation (can be assessed by dynamic light scattering)
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Oxidation of critical residues
How can researchers design effective experiments to study TGB2-host protein interactions?
Understanding TGB2 interactions with host factors is crucial for elucidating the mechanism of viral movement.
Methodological approaches:
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Yeast two-hybrid screening: Identify potential host interactors.
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Co-immunoprecipitation: Confirm direct protein-protein interactions.
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Mass spectrometry: Identify TGB2-associated protein complexes from infected plant tissue.
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BiFC or FRET analysis: Visualize interactions in plant cells.
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Virus-induced gene silencing (VIGS): Knockdown identified host factors to determine their role in TGB2 function.
Based on studies of similar proteins, potential host interactors might include fibrillarin (Fib2), components of the endocytic pathway, and RNA-binding proteins that may antagonize viral infection (like G3BP in other systems) .
How should researchers analyze contradictory data regarding TGB2 function?
When facing contradictory results in TGB2 studies, consider:
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Host species differences: TGB2 may function differently in various host plants. Studies should specify whether experiments were conducted in natural hosts or experimental systems like Nicotiana benthamiana.
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Experimental conditions: Temperature, light cycles, and plant age can affect viral movement protein functions.
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Protein expression levels: Overexpression from the 35S promoter may yield different results than expression from viral subgenomic promoters in a virus context .
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Potential redundancy: Other viral proteins may compensate for TGB2 mutations in some experimental systems.
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Technical considerations: Protein tags may affect function or localization in some contexts but not others.
What statistical approaches are appropriate for analyzing TGB2 localization data?
For quantitative analysis of microscopy data:
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Co-localization analysis: Calculate Pearson's or Manders' coefficients to quantify the degree of overlap between TGB2 and cellular markers.
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Particle tracking: For mobile TGB2-containing granules, analyze velocity, directionality, and association with cytoskeletal elements.
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Fluorescence intensity measurements: Quantify relative distribution across cellular compartments.
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Sample size determination: For cellular phenotypes, analyze at least 50-100 cells across 3 independent experiments for statistical robustness.
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Appropriate statistical tests: Use non-parametric tests when data doesn't follow normal distribution, which is common in localization studies.
What emerging technologies could advance our understanding of TGB2 function?
Several cutting-edge approaches could provide new insights:
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Cryo-electron microscopy: To determine high-resolution structures of TGB2 in membrane environments.
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Single-molecule tracking: To follow individual TGB2 molecules in live cells.
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Optogenetics: To control TGB2 localization or function with light.
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CRISPR-based screening: To identify host factors required for TGB2 function.
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Liquid-liquid phase separation (LLPS) analysis: To investigate whether TGB2 forms membraneless organelles similar to other viral movement proteins .
How might comparative analysis of TGB2 across different viruses inform functional understanding?
Cross-species comparison can reveal:
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Conserved functional domains: Alignments of TGB2 proteins from different viruses could identify critical regions.
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Host-specific adaptations: Differences in TGB2 sequences may reflect adaptations to different host plants.
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Evolutionary insights: Phylogenetic analysis could reveal how TGB2 evolved in relation to host resistance mechanisms.
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Functional predictions: Features shared with well-characterized TGB2 proteins (like those from potato mop-top virus) could suggest functions not yet demonstrated for WCMV TGB2 .
This comparative approach is particularly valuable given the evidence for subtle differences in subcellular localizations of TGB proteins between the hordei-, pomo-, and potex-like groups, which may indicate differences in functional roles .
