Recombinant Aura virus Structural polyprotein
Description
Autoproteolytic Mechanism
The CP’s C-terminal domain functions as a serine protease with cis- and trans-cleavage activities:
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Catalytic triad: His145, Asp163, Ser218 (Aura virus numbering) .
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Cleavage site: Trp267-Ser268, conserved across alphaviruses .
Crystallographic studies of the truncated CP (AVCPΔ2, residues 110–265) resolved to 1.81 Å (PDB ID: 4UON) reveal:
Table 2: Enzymatic Parameters of Recombinant AVCPΔ2
| Parameter | Value |
|---|---|
| K<sub>m</sub> | 2.63 ± 0.62 µM |
| k<sub>cat</sub>/K<sub>m</sub> | 4.97 × 10<sup>4</sup> M<sup>−1</sup> min<sup>−1</sup> |
Applications in Antiviral Research
rAVSP is pivotal for:
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Drug discovery: FRET-based assays using fluorogenic substrates (e.g., Abz-EPQ↓SYYY-EDDnp) enable high-throughput screening of protease inhibitors .
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Structural studies: Cryo-EM and X-ray crystallography of recombinant CP elucidate mechanisms of capsid-glycoprotein interactions .
Challenges and Future Directions
Product Specs
Note: We will prioritize shipping the format currently in stock. However, if you have a specific format requirement, please indicate it during order placement. We will fulfill your request if possible.
Note: All our proteins are shipped with standard blue ice packs. If you require dry ice shipping, please inform us in advance. Additional fees may apply.
Generally, the shelf life of liquid forms is 6 months at -20°C/-80°C. The shelf life of lyophilized forms is 12 months at -20°C/-80°C.
Target Background
The E3/E2 precursor translocates to the host endoplasmic reticulum, driven by the signal sequence provided by the E3 protein. Furin cleavage of E3 results in its association with spike glycoprotein E1, contributing to pH protection of E1 during transport through the secretory pathway. Following virion release from the host cell, E3 is gradually released in the extracellular space.
The E2 protein plays a crucial role in viral attachment to the target host cell by binding to the cell receptor. It is synthesized as a p62 precursor, which is processed by furin at the cell membrane just before virion budding. This processing generates the E2-E1 heterodimer. The p62-E1 heterodimer remains stable, while E2-E1 is unstable and dissociates at low pH. p62 undergoes the final processing step, likely to prevent premature E1 fusion activation before its final export to the cell surface. The C-terminus of E2 contains a transitory transmembrane domain, which is disrupted by palmitoylation. This disruption reorients the C-terminal tail from the lumenal to the cytoplasmic side. This step is critical, as the E2 C-terminus interacts with capsid proteins during budding. This release of the E2 C-terminus into the cytoplasm occurs late in protein export, preventing premature particle assembly at the endoplasmic reticulum membrane.
The 6K protein is a constitutive membrane protein involved in virus glycoprotein processing, cell permeabilization, and budding of viral particles. It disrupts cellular calcium homeostasis, likely at the endoplasmic reticulum level, leading to elevated cytoplasmic calcium. Due to its lipophilic properties, 6K is postulated to influence lipid selection for interaction with the transmembrane domains of glycoproteins. This affects the deformability of the bilayer, crucial for the extreme curvature during budding. The 6K protein is present in virions at low levels, approximately 3% compared to viral glycoproteins.
The E1 protein is a class II viral fusion protein. Its fusion activity is inactive as long as E1 remains bound to E2 in the mature virion. After virus attachment to the target cell and endocytosis, acidification of the endosome induces dissociation of the E1/E2 heterodimer, accompanied by trimerization of the E1 subunits. This E1 trimer becomes fusion-active and promotes release of the viral nucleocapsid into the cytoplasm after fusion of the endosome and viral membranes. Efficient fusion requires the presence of cholesterol and sphingolipid in the target membrane. Optimal fusion occurs with a ratio of approximately one cholesterol molecule to two phospholipid molecules and is specific for sterols containing a 3-beta-hydroxyl group.
KEGG: vg:944526
Q&A
What is the composition of the Aura virus structural polyprotein?
The Aura virus structural polyprotein is encoded in the 3' one-third of the alphavirus genome and is translated from a 4.2-kb subgenomic mRNA. This polyprotein is subsequently cleaved into five distinct proteins: the nucleocapsid/capsid protein (CP) (~30 kDa), two envelope glycoproteins - E1 (~52 kDa) and E2 (~49 kDa), and two small peptides - E3 (~10 kDa) and 6K (~6 kDa) . The structural proteins of Aura virus share considerable sequence identity with those of Sindbis virus (SINV): 77% for CP, 56% for E2, and 61% for E1, resulting in an average identity of 62% . Understanding this composition is fundamental for any recombinant expression system design targeting these proteins.
How does the Aura virus capsid protein function in polyprotein processing?
The Aura virus capsid protein possesses a critical cis-proteolytic activity that is essential for its self-release from the nascent structural polyprotein. Following its autocatalytic release, the capsid protein participates in viral genome encapsidation and nucleocapsid core formation . Recent research has revealed that the capsid protease also demonstrates trans-proteolytic activity, which has been characterized using a FRET-based assay. Kinetic parameters for this activity include a Km value of 2.63 ± 0.62 μM and a kcat/Km value of 4.97 × 104 M−1min−1 . This dual proteolytic functionality makes the capsid protein a potential target for antialphaviral therapeutics that could inhibit both polyprotein processing and subsequent virus assembly.
What structural features characterize the Aura virus particles?
Cryoelectron microscopy and three-dimensional image reconstruction analysis have revealed that Aura virus particles exhibit a T=4 icosahedral structure similar to other alphaviruses . Despite previous studies with negative staining that suggested potential T=3 structures or size variants, higher-resolution analysis demonstrates that particles from both top and bottom components of sucrose gradients (designated Aura T and Aura B) have indistinguishable T=4 structures at 22-Å resolution . Comparative structural analyses between Aura virus and Sindbis virus have identified subtle differences, including a ~6° counterclockwise rotation of hexamers and pentamers in the core and transmembrane bundles of Aura virus relative to SINV, suggesting potential variations in CP-glycoprotein binding orientations .
What methodologies are recommended for recombinant expression of Aura virus structural polyprotein?
For successful recombinant expression of Aura virus structural polyprotein, researchers should consider self-replicating RNA systems based on alphavirus biology. These systems typically involve:
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DNA-launched replicon vectors: Constructing plasmids containing the Aura virus structural genes under the control of a cytomegalovirus (CMV) promoter enables efficient expression in mammalian cells .
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Two-component trans-replication system: This approach separates the nonstructural and structural components, allowing for controlled expression and functional studies. The system involves co-expression of P123 (nonstructural polyprotein) and nsP4 with a replication-competent template RNA containing reporter genes under genomic and subgenomic promoters .
| Expression System | Components | Applications | Advantages |
|---|---|---|---|
| DNA-launched replicon | CMV promoter, structural gene cassette | Protein production, vaccine development | High-level expression, self-amplification |
| Trans-replication system | P123 + nsP4 expression vectors, template RNA with reporters | Functional studies, inhibitor screening | Sensitive detection, mimics natural replication complexes |
When designing expression constructs, researchers should maintain the natural protease cleavage sites to ensure proper processing of the structural polyprotein. Expression in BHK cells has proven effective for producing viable Aura virus particles with proper structural organization .
How can structure-guided mutagenesis be employed to study Aura virus structural proteins?
Structure-guided mutagenesis represents a powerful approach for investigating the functional significance of specific structural features in Aura virus proteins. Based on recent structural studies, the following methodological framework is recommended:
This integrated approach enables researchers to establish structure-function relationships for specific residues and domains within the Aura virus structural polyprotein.
What are the conformational changes in the active site of Aura virus capsid protease during substrate binding?
The crystal structure of the trans-active form of Aura virus capsid protease (AVCP) at 1.81-Å resolution has revealed critical conformational changes associated with proteolytic activity . When comparing the active form with substrate-bound mutant and inactive blocked forms:
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Active site configuration: The catalytic triad (likely composed of His, Asp, and Ser residues based on serine protease homology) undergoes repositioning to facilitate nucleophilic attack during peptide bond hydrolysis .
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Oxyanion hole formation: Structural reorganization creates a stabilizing pocket for the negative charge that develops on the carbonyl oxygen during the transition state of proteolysis .
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Substrate specificity pocket dynamics: Residues forming the S1 and S1' pockets adapt to accommodate the P1 and P1' residues of the substrate, explaining the preference for specific amino acid sequences at the cleavage site .
These conformational changes provide critical insights for rational drug design targeting the capsid protease. Inhibitors that can lock the protease in an inactive conformation or that mimic the transition state would potentially block both cis- and trans-proteolytic activities, thereby inhibiting viral replication .
How does RNA content affect the structural organization of recombinant Aura virus particles?
Aura virus uniquely encapsidates both genomic RNA (11.8 kb) and subgenomic RNA (4.2 kb), resulting in virus particles that separate into two components in sucrose gradients . Despite this biochemical separation and apparent size differences observed in negative staining:
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Structural consistency: Cryoelectron microscopy reconstructions computed to resolutions of 17 Å (top component) and 21 Å (bottom component) revealed that both components maintain virtually identical T=4 icosahedral structures .
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Radial density comparison: Correlation coefficient analysis as a function of radius between Aura T and Aura B reconstructions demonstrated that both glycoprotein and nucleocapsid protein layers are almost identical, despite differences in RNA content .
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Comparative analysis with other alphaviruses: Difference maps and superimposed wire-frame representations comparing Aura virus with Sindbis virus revealed subtle structural variations, including a ~6° counterclockwise rotation of capsomeres in Aura virus .
These findings suggest that the T=4 organization is fundamentally robust and not significantly altered by differences in the encapsidated RNA. This structural stability has important implications for designing recombinant viruses with altered RNA content or chimeric genomes.
What screening methodologies exist for identifying inhibitors of Aura virus capsid protease?
The development of a FRET-based trans-proteolytic activity assay for Aura virus capsid protease (AVCP) has provided a valuable tool for screening potential protease inhibitors . This assay offers several methodological advantages:
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Assay principle: The FRET-based system utilizes fluorogenic peptide substrates containing specific cleavage sequences recognized by the capsid protease. Peptide cleavage separates the fluorophore from the quencher, resulting in measurable fluorescence increases proportional to proteolytic activity .
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Kinetic parameter determination: The assay enables precise measurement of enzyme kinetics, with established parameters for AVCP including a Km value of 2.63 ± 0.62 μM and a kcat/Km value of 4.97 × 104 M−1min−1 .
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Inhibitor screening workflow:
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Primary screening against a diverse compound library
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Dose-response analysis of hit compounds
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Selectivity profiling against related serine proteases
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Mechanism of action studies using kinetic analysis
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Structural characterization of inhibitor binding using X-ray crystallography
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This screening approach, combined with the available 1.81-Å resolution crystal structure of the trans-active form of AVCP, provides a robust platform for structure-based drug design targeting the capsid protease .
How can the dynamics of Aura virus structural proteins be characterized in solution?
Understanding the dynamic nature of Aura virus structural proteins requires complementary biophysical approaches. Based on successful studies of related alphavirus proteins, the following methodological framework is recommended:
These approaches can reveal critical insights into the conformational dynamics associated with various functions of the structural polyprotein, including autoproteolytic processing, RNA binding, and assembly interactions.
What are the key considerations for developing a trans-replication system for Aura virus?
The development of a trans-replication system for Aura virus would enable detailed studies of viral replication and transcription mechanisms. Based on successful systems for related alphaviruses, the following methodological considerations are important:
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Component design:
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P123 expression construct: Contains the coding sequence for nonstructural proteins 1-3
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nsP4 expression construct: Contains the coding sequence for the RNA-dependent RNA polymerase
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Template RNA: Incorporates the 5' and 3' untranslated regions of Aura virus along with reporter genes under the control of genomic and subgenomic promoters
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Reporter selection:
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Experimental validation:
This system offers exceptional sensitivity for detecting the effects of mutations or inhibitors on viral RNA synthesis, as demonstrated for Ross River virus . The approach separates replication from virus production, enabling the study of mutations that might be lethal in the context of an infectious clone.
How can structural comparisons between Aura virus and other alphaviruses inform recombinant virus design?
Structural comparison between Aura virus and other alphaviruses provides critical insights for rational design of recombinant viruses with desired properties. The methodological approach involves:
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Cryo-EM analysis and 3D reconstruction:
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Quantitative structural comparison:
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Structure-guided recombinant design:
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Identification of conserved structural elements essential for virus assembly
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Mapping of variable regions suitable for modification
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Rational design of chimeric viruses based on structural compatibility
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Specific findings from Aura virus studies reveal that despite high sequence identity with Sindbis virus structural proteins (average 62%), subtle structural differences exist, including a ~6° counterclockwise rotation of capsomeres . This understanding enables precise engineering of recombinant viruses with predictable structural properties.
How can researchers address challenges in expressing functional recombinant Aura virus structural polyprotein?
Expression of functional recombinant Aura virus structural polyprotein can present several challenges that researchers should be prepared to address:
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Proteolytic processing issues:
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Problem: Improper processing of the structural polyprotein
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Solution: Ensure intact protease domain in the capsid protein; verify that the C-terminal two residues crucial for protease activity are preserved
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Analysis method: Western blot analysis with antibodies against individual structural proteins to monitor processing
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Protein misfolding and aggregation:
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Problem: Recombinant structural proteins form insoluble aggregates
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Solution: Optimize expression conditions (temperature, induction parameters); consider fusion tags that enhance solubility; explore co-expression with chaperones
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Analysis method: Size-exclusion chromatography and dynamic light scattering to assess oligomeric state and aggregation
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RNA encapsidation efficiency:
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Problem: Poor RNA packaging in recombinant virus-like particles
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Solution: Verify the presence of packaging signals in template RNA; ensure proper ratio of structural proteins to RNA
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Analysis method: Quantitative RT-PCR of extracted RNA from purified particles
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Structural protein interactions:
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Problem: Inefficient assembly of structural proteins
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Solution: Ensure proper glycosylation of envelope proteins in the expression system; maintain natural cleavage sites between structural proteins
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Analysis method: Cryo-EM analysis to verify proper T=4 assembly structure
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These troubleshooting approaches are essential for successful expression and analysis of functional recombinant Aura virus structural proteins.
How can researchers differentiate between genomic and subgenomic RNA-containing Aura virus particles?
Given Aura virus's unique ability to encapsidate both genomic and subgenomic RNA, researchers may need to differentiate between these particle populations:
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Density gradient separation:
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Method: Sucrose or iodixanol gradient ultracentrifugation
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Analysis: Particles containing genomic RNA typically migrate to the upper component (Aura T), while a mixture of genomic and subgenomic RNA-containing particles is found in the lower component (Aura B)
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Validation: Analyze RNA content from each fraction using denaturing agarose gel electrophoresis
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RNA content analysis:
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Method: Phenol-chloroform extraction of RNA from purified virus particles
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Analysis: Northern blot or RT-PCR using probes/primers specific to genomic or subgenomic regions
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Quantification: Determine the ratio of genomic to subgenomic RNA by quantitative RT-PCR
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Structural characterization:
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Method: Cryo-electron microscopy and image reconstruction
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Analysis: Compare particles from different gradient fractions to identify potential structural differences
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Note: Previous studies have shown that despite differences in RNA content, Aura T and Aura B particles maintain virtually identical T=4 structures at current resolution limits
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These methodological approaches enable accurate characterization of heterogeneous Aura virus particle populations based on their RNA content.
How should researchers interpret structural differences between Aura virus and other alphaviruses?
When analyzing structural data comparing Aura virus with other alphaviruses like Sindbis virus (SINV) or Ross River virus (RRV), researchers should consider:
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Difference map interpretation:
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Radial correlation analysis:
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Rotational differences:
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Evolutionary implications:
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Structural differences despite high sequence identity (62% average) may reflect adaptation to different hosts or transmission mechanisms
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Compare with structural data from other alphaviruses to identify conserved vs. variable features across the genus
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Understanding these structural differences is crucial for rational design of recombinant viruses and for identifying potential targets for antiviral development.
What does the intrinsic disorder in alphavirus proteins reveal about structural polyprotein function?
Recent structural studies of alphavirus proteins, including nsP4 and capsid protease, have revealed significant intrinsic disorder that has functional implications:
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Functional flexibility:
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Hydrogen-deuterium exchange mass spectrometry (HDX-MS) and nuclear magnetic resonance (NMR) studies have shown that alphavirus nsP4 is highly dynamic with an intrinsically disordered N-terminal domain
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This flexibility likely facilitates interactions with multiple protein partners and RNA substrates during replication
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Regulated proteolysis:
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Conformational adaptability:
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Intrinsically disordered regions in structural proteins may allow for conformational adaptations during virus assembly
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These regions could facilitate the transition from free polyprotein to assembled virus particle
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Data interpretation guidelines:
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High B-factors in crystal structures suggest dynamic regions
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Rapid hydrogen-deuterium exchange indicates solvent-exposed, flexible regions
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Missing electron density in X-ray structures often corresponds to disordered segments
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Broadened or missing NMR signals indicate conformational exchange or disorder
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This intrinsic disorder represents an important consideration for recombinant expression systems and structural studies, as conditions that stabilize particular conformations may be necessary for successful analysis.
