Recombinant Vaccinia virus Protein OPG190 (OPG190), partial

What is OPG190 and what are its structural characteristics?

OPG190 (also known as Protein B5, Plaque-size/host range protein, OPG19, PS/HR, VACWR187, or B5R) is a vaccinia virus protein that plays critical roles in viral membrane dynamics and host cell entry.

Key structural characteristics:

• Molecular weight: 31.4-33.2 kDa (depending on the construct)

• Available as recombinant protein with N-terminal 6xHis-tag

• Typically produced as a partial protein fragment (amino acids 17-279)

• Associated with UniProt IDs: Q01227 and P24083

• Gene ID: 75279723

OPG190 is a membrane protein that localizes to the outermost envelope of extracellular virions. Its structure facilitates both the wrapping of intracellular mature virions (IMV) and the dissolution of the external membrane during host cell entry .

What expression systems are used for producing recombinant OPG190?

The primary expression system used for producing recombinant OPG190 is E. coli. The production methodology typically involves:

• Cloning the OPG190 gene into an appropriate expression vector (such as pRB21 or similar)

• Transformation into E. coli competent cells

• Induction of protein expression (typically using IPTG for T7 promoter-based systems)

• Purification via affinity chromatography using the N-terminal His-tag

The expressed protein demonstrates >90% purity when analyzed by SDS-PAGE . The recombinant protein is typically formulated and lyophilized in a buffer containing PBS (pH 7.4), 0.02% NLS, 1mM EDTA, 4% Trehalose, and 1% Mannitol to enhance stability .

How does OPG190 function in vaccinia virus infection?

OPG190 serves multiple critical functions during the vaccinia virus lifecycle:

• Virion Membrane Dynamics: OPG190 participates in the wrapping of intracellular mature virions (IMV) to form intracellular enveloped virions (IEV)

• Host Cell Entry: The protein facilitates the dissolution of the outermost membrane of extracellular enveloped virions (EEV), which is a crucial step for the virus to enter host cells

• Host Range Determination: As indicated by its synonym "Plaque-size/host range protein," OPG190 influences viral tropism and the efficiency of infection in different cell types

• Evolutionary Adaptability: Recent research suggests OPG190 may be involved in the "genomic accordion" evolutionary strategy employed by orthopoxviruses, potentially allowing for adaptive genetic flexibility

What methodologies are recommended for reconstitution and storage of recombinant OPG190?

For optimal handling of recombinant OPG190:

Reconstitution Protocol:

• Always centrifuge tubes before opening to collect material at the bottom

• Reconstitute to a concentration greater than 100 μg/ml in distilled water

• Avoid vortexing or vigorous pipetting during reconstitution

• Aliquot the reconstituted solution to minimize freeze-thaw cycles

Storage Recommendations:

• Ship with dry ice to maintain stability

• Store at -20°C/-80°C upon receipt

• Avoid repeated freezing and thawing

• For long-term storage, maintain aliquots at -80°C

How can recombinant OPG190 be used to study virus-host interactions?

Recombinant OPG190 serves as a valuable tool for investigating several aspects of virus-host interactions:

Experimental Approaches:

• Protein-Protein Interaction Studies:

  • Use purified recombinant OPG190 in pull-down assays to identify host cellular binding partners

  • Employ yeast two-hybrid or mammalian two-hybrid systems to validate interactions

  • Perform co-immunoprecipitation experiments in infected cells

• Functional Assays:

  • Competitive inhibition experiments using recombinant OPG190 to block native protein function

  • Cell entry assays comparing wild-type vs. OPG190-depleted virions

  • Membrane fusion assays to assess the role of OPG190 in membrane dynamics

• Structural Biology Applications:

  • X-ray crystallography of OPG190 to determine three-dimensional structure

  • Cryo-electron microscopy of OPG190 in the context of viral particles

  • Epitope mapping to identify functionally important regions

These approaches can provide insights into the molecular mechanisms by which OPG190 mediates viral entry and membrane fusion events, potentially revealing novel targets for antiviral intervention .

What techniques are effective for generating recombinant vaccinia virus expressing modified OPG190?

The generation of recombinant vaccinia virus expressing modified OPG190 involves a multi-step process:

Detailed Methodology:

• Construction of Targeting Vectors:

  • Clone the modified OPG190 gene into an appropriate shuttle vector (e.g., pRB21)

  • Incorporate desired modifications such as fluorescent tags (e.g., GFP fusion)

  • Verify the construct by restriction digestion and sequencing

• Virus Infection and DNA Transfection:

  • Seed BS-C-1 cells (chosen for their ability to form large visible plaques)

  • Infect cells with vRB12 (vaccinia virus lacking the VP37 gene)

  • Transfect infected cells with the targeting vector containing modified OPG190

  • Incubate for 48-72 hours to allow for homologous recombination

• Selection of Recombinant Virus:

  • Isolate large plaques, which indicate successful recombination

  • Perform multiple rounds of plaque purification (typically three)

  • Validate recombinant virus by PCR and/or Western blotting

  • Expand validated recombinant viruses in cell culture

This approach has been successfully used to generate recombinant vaccinia viruses expressing various proteins to study their effects on virus-induced cell death, including necroptosis .

What role does OPG190 play in the "genomic accordion" evolutionary strategy of orthopoxviruses?

The "genomic accordion" refers to a mechanism whereby orthopoxviruses, including vaccinia and monkeypox viruses, can rapidly adapt through genomic expansion and contraction, particularly in low-complexity regions (LCRs).

OPG190's Role in Genomic Adaptation:

• Evolutionary Flexibility:

  • OPG190 belongs to a class of orthopoxvirus genes (OPGs) that demonstrate variability consistent with genomic accordion strategies

  • Changes in OPG190 may affect expression, translation, stability, or function in ways that confer adaptive advantages

• Relationship to Low-Complexity Regions (LCRs):

  • Research indicates that LCRs near OPG genes, including those potentially affecting OPG190, can influence gene expression and function

  • These variations may contribute to differences in virulence, host range, and immune evasion

• Comparative Analysis:

  Gene	LCR Association	Evolutionary Implication
  OPG190	Promoter/ATG Start	Potential variation in expression level
  OPG153	Documented variability	Affected by genomic accordion
  OPG204	Documented variability	Affected by genomic accordion
  OPG208	ATG Start/Promoter	Potential expression variation

Recent studies suggest that rather than focusing solely on single nucleotide polymorphisms (SNPs), researchers should examine LCR variability to better understand phenotypic differences between orthopoxvirus strains and their evolutionary trajectories .

How can researchers optimize experimental design when studying OPG190 functions?

When designing experiments to investigate OPG190 functions, researchers should consider several methodological approaches:

Experimental Design Considerations:

• Protein Expression and Purification:

  • Expression in E. coli systems yields high purity (>90% by SDS-PAGE)

  • Consider protein tags carefully—N-terminal His-tags are common but may affect function

  • Validate protein folding using circular dichroism or limited proteolysis

  • Test multiple buffer conditions to optimize stability

• Functional Assays:

  • Use complementary approaches to validate findings:

    • In vitro binding assays with purified components

    • Cell-based assays in relevant host cell types

    • In vivo models where appropriate

  • Include appropriate controls:

    • Wild-type OPG190

    • Non-functional mutants

    • Related proteins from other orthopoxviruses

• Advanced Imaging Techniques:

  • Confocal microscopy to track OPG190 localization

  • Live cell imaging to monitor dynamics during infection

  • Super-resolution microscopy for detailed localization studies

  • Correlative light and electron microscopy for structural context

• Data Analysis Protocols:

  • Quantitative analysis of membrane fusion events

  • Statistical approaches appropriate for biological replicates

  • Image analysis algorithms for objective quantification

These methodological considerations can help ensure robust, reproducible research on OPG190 function in various experimental contexts .

How does OPG190 relate to other orthopoxvirus proteins, and what comparative approaches can be used?

OPG190 is part of a larger network of orthopoxvirus proteins involved in virion structure, membrane dynamics, and host interactions.

Comparative Analysis Approaches:

• Sequence-Based Comparisons:

  • Multiple sequence alignments of OPG190 orthologs across orthopoxviruses

  • Identification of conserved domains and variable regions

  • Phylogenetic analysis to trace evolutionary relationships

• Functional Comparisons:

  Virus	Protein Ortholog	Functional Similarity	Key Differences
  Vaccinia virus	OPG190/B5R	Reference protein	-
  Monkeypox virus	Orthologous OPG	Similar membrane roles	May have host-specific adaptations
  Variola virus	B5R ortholog	Conserved structure	Differences may contribute to human specificity

• Complementation Studies:

  • Replace OPG190 in vaccinia virus with orthologs from other poxviruses

  • Assess the ability of heterologous proteins to rescue OPG190 deficiency

  • Identify species-specific functional elements

• Structural Biology Approaches:

  • Comparative modeling of OPG190 orthologs

  • Analysis of conserved and variable structural elements

  • Identification of potential binding interfaces

These comparative approaches can provide insights into the common and divergent functions of OPG190 orthologs across the orthopoxvirus family, potentially revealing mechanisms of host adaptation and virulence .

What protocols are most effective for analyzing OPG190 interactions with viral and cellular membranes?

Given OPG190's role in viral membrane dynamics, specialized methods for studying these interactions are essential:

Recommended Methodologies:

• Biochemical Membrane Binding Assays:

  • Liposome binding assays using recombinant OPG190

  • Flotation assays to assess membrane association

  • Surface plasmon resonance with immobilized membrane components

• Biophysical Approaches:

  • Atomic force microscopy to visualize membrane interactions

  • Fluorescence recovery after photobleaching (FRAP) to measure membrane dynamics

  • Fluorescence resonance energy transfer (FRET) to detect protein-protein interactions within membranes

• Cryo-Electron Microscopy:

  • Visualization of OPG190 in the context of intact virions

  • Structural analysis of membrane deformation induced by OPG190

  • Immunogold labeling to localize OPG190 precisely within virion structures

• Live Cell Imaging:

  • Real-time tracking of fluorescently labeled OPG190 during viral entry

  • Simultaneous imaging of viral and cellular membrane markers

  • Quantification of membrane fusion events mediated by OPG190

How can researchers distinguish between direct and indirect effects of OPG190 in experimental systems?

Determining causality in complex biological systems requires careful experimental design:

Methodological Approaches:

• Genetic Manipulation Strategies:

  • Generate OPG190-null viruses and perform complementation studies

  • Use inducible expression systems to control timing of OPG190 expression

  • Create point mutations in functional domains rather than complete deletions

  • Employ CRISPR/Cas9 to modify endogenous OPG190 in viral genomes

• Biochemical Validation:

  • In vitro reconstitution of minimal systems to test direct effects

  • Use purified components to determine if interactions require additional factors

  • Employ proximity labeling techniques (BioID, APEX) to identify proteins in close association with OPG190

• Temporal Analysis:

  • Use time-resolved studies to establish order of events

  • Employ rapid inhibition strategies (e.g., small molecule inhibitors, photo-caged proteins)

  • Correlate OPG190 activity with specific stages of viral replication

• Controls and Validation:

  • Include related but functionally distinct viral proteins as controls

  • Validate findings across multiple cell types and experimental conditions

  • Use complementary methodologies to confirm key findings

What analytical techniques are recommended for studying OPG190's role in the genomic accordion phenomenon?

Investigating OPG190 in the context of the genomic accordion evolutionary strategy requires specialized approaches:

Analytical Framework:

• Genomic Analysis:

  • Next-generation sequencing to identify variations in OPG190 and associated LCRs

  • Comparative genomics across orthopoxvirus isolates

  • Analysis of selection pressure using dN/dS ratios

• Expression Analysis:

  • Quantitative PCR to measure transcript levels

  • Ribosome profiling to assess translation efficiency

  • Western blotting to determine protein expression levels in different viral strains

• Functional Impact Assessment:

  • Construction of chimeric viruses with OPG190 variants

  • Fitness assays comparing growth kinetics of viruses with different OPG190 alleles

  • Host range determination using diverse cell types

• Bioinformatic Approaches:

  • Prediction of functional impacts of sequence variations

  • Structural modeling of variant proteins

  • Analysis of low-complexity regions associated with OPG190

These analytical techniques can help researchers understand how variations in OPG190 contribute to viral adaptation and evolution through the genomic accordion mechanism.

What are common challenges in working with recombinant OPG190 and how can they be addressed?

Researchers may encounter several technical challenges when working with recombinant OPG190:

Challenge 1: Protein Solubility and Stability

• Problem: OPG190 may form aggregates or precipitate during purification or storage.

• Solutions:

  • Optimize buffer conditions (consider adding glycerol, detergents for membrane proteins)

  • Use fusion partners that enhance solubility (MBP, SUMO)

  • Purify under native conditions when possible

  • Store in buffer containing stabilizers like trehalose and mannitol

Challenge 2: Functional Activity Preservation

• Problem: Recombinant OPG190 may lose functional activity during purification.

• Solutions:

  • Validate activity using binding assays

  • Consider tag position (N- vs C-terminal) to minimize interference

  • Include proper controls to ensure observed effects are specific

  • Test multiple expression and purification strategies

Challenge 3: Reproducibility in Complex Assays

• Problem: Variability in results when using OPG190 in cell-based assays.

• Solutions:

  • Standardize protein preparation methods

  • Validate protein activity before each experiment

  • Include internal controls

  • Report detailed methodologies including lot numbers

How can researchers validate that their recombinant OPG190 maintains native conformational properties?

Ensuring that recombinant OPG190 maintains its native conformation is critical for valid experimental outcomes:

Validation Strategies:

• Structural Analysis:

  • Circular dichroism spectroscopy to assess secondary structure

  • Thermal shift assays to evaluate protein stability

  • Limited proteolysis to probe for properly folded domains

  • Native PAGE to analyze oligomeric state

• Functional Validation:

  • Binding assays with known interaction partners

  • Activity assays based on known functions

  • Comparison with native protein isolated from virions when possible

• Immunological Approaches:

  • Reactivity with conformation-specific antibodies

  • Epitope mapping to ensure proper domain folding

  • Comparison of antigenicity with virus-derived protein

• Biophysical Characterization:

  • Size-exclusion chromatography to assess monodispersity

  • Dynamic light scattering to check for aggregation

  • Mass spectrometry to confirm post-translational modifications if applicable

What emerging technologies could advance our understanding of OPG190 function?

Several cutting-edge technologies hold promise for deeper insights into OPG190 biology:

• Cryo-Electron Tomography:

  • Visualization of OPG190 in its native context within intact virions

  • 3D reconstruction of membrane deformation events mediated by OPG190

  • Correlative light and electron microscopy for targeted analysis

• Single-Molecule Techniques:

  • Single-molecule FRET to study conformational changes

  • Optical tweezers to measure forces involved in membrane interactions

  • Super-resolution microscopy to track individual OPG190 molecules during infection

• Integrative Structural Biology:

  • Combining X-ray crystallography, NMR, and cryo-EM data

  • Molecular dynamics simulations of OPG190-membrane interactions

  • Computational prediction of interaction networks

• Advanced Genetic Engineering:

  • CRISPR-based screening to identify host factors interacting with OPG190

  • Synthetic biology approaches to create minimal systems for OPG190 function

  • In vivo DNA and RNA imaging to visualize genomic accordion dynamics

How might research on OPG190 contribute to our understanding of broader orthopoxvirus biology?

Research on OPG190 has implications that extend beyond the protein itself:

Broader Impacts:

• Evolutionary Biology:

  • Insights into how orthopoxviruses adapt to new hosts through genomic accordion mechanisms

  • Understanding the balance between conservation and variability in viral proteins

  • Models for predicting emerging virus characteristics

• Virus-Host Interactions:

  • Mechanisms of viral entry and membrane fusion

  • Strategies for evading host immune responses

  • Common principles across the orthopoxvirus family

• Translational Applications:

  • Target identification for antiviral development

  • Rational design of attenuated vaccine strains

  • Diagnostic tools based on conserved vs. variable regions of OPG190

• Fundamental Virology:

  • Principles of viral assembly and disassembly

  • Coordination between different viral proteins during infection

  • Role of membrane dynamics in viral replication cycles

By advancing our understanding of OPG190, researchers can contribute to broader knowledge of orthopoxvirus biology, potentially leading to new therapeutic and preventative strategies.