Recombinant African swine fever virus Uncharacterized protein F165R (War-056)

What is the F165R (War-056) protein?

F165R (War-056) is an uncharacterized protein encoded by the African swine fever virus (ASFV) genome. It is also known as pF165R and is a full-length protein consisting of 165 amino acids. Despite being classified as "uncharacterized," research interest in this protein has increased due to the significant global threat ASFV poses to the pig industry and food security. F165R is one of several ASFV proteins that may contribute to viral pathogenesis, though its specific functions remain under investigation .

What is the amino acid sequence and structural information available for F165R?

The complete amino acid sequence of F165R (War-056) consists of 165 amino acids as follows:

MANPNKRIMNKKSKQASISSILNFFFFYIMEYFVAVDNETSLGVFTSIEQCEETMKQYPGLHYVVFKYTCPADAENTDVVYLIPSLTLHTPMFVDHCPNRTKQARHVLKKINLVFEEEEIENWKVSVNTVFPHVHNRLSAPKLSIDEANEAVEKFLIQAGRLMSL

While detailed three-dimensional structural information has not been fully elucidated, bioinformatic analyses suggest the protein may contain functional domains that interact with host cellular machinery. The protein has a UniProt ID of P0CA69 . Current research approaches are focusing on structural biology techniques to determine its precise conformation and functional regions.

How does F165R relate to other characterized ASFV proteins?

F165R exists within the broader context of ASFV proteins, some of which have established roles in virulence. Unlike well-characterized virulence determinants such as MGF_505/360 and EP402R that have been shown to significantly impact viral pathogenicity, F165R's specific contribution to viral fitness remains less defined . Comparative genomic analyses between attenuated and virulent ASFV strains suggest that F165R may be part of the genetic variations that influence virulence, though not necessarily as a primary determinant like the UK (DP96R) gene or the 9GL gene, which have been directly manipulated to create attenuated vaccine candidates .

What experimental approaches are recommended for studying F165R function?

To investigate F165R function, researchers should consider a multi-faceted approach:

• Gene Knockout/Modification Studies: Creating recombinant ASFV strains with deletions or modifications of the F165R gene to observe effects on viral replication, morphology, and pathogenicity, similar to approaches used with the 9GL gene .

• Protein-Protein Interaction Assays: Employing co-immunoprecipitation, yeast two-hybrid screens, or proximity labeling techniques to identify host or viral interaction partners.

• Comparative Genomics: Analyzing F165R sequence conservation and variations across the 24 known ASFV genotypes, particularly focusing on differences between attenuated and virulent strains .

• Localization Studies: Using fluorescently tagged F165R proteins to determine subcellular localization during infection cycles.

• Functional Complementation: Testing whether F165R can restore function in attenuated strains lacking specific virulence factors.

These methodologies should be implemented within appropriate biosafety conditions given ASFV's classification as a high-consequence pathogen.

How might F165R contribute to ASFV genotype recombination events?

Recent research has identified naturally occurring recombinant ASFVs carrying mosaic genomes of genotype I and II that exhibit high lethality and transmissibility in pigs . While specific data on F165R's role in recombination is not explicitly detailed in the available research, its potential contribution should be investigated in the context of these recombination events.

Researchers should consider:

• Examining whether F165R sequence variations correlate with recombination hotspots in the viral genome

• Investigating if F165R protein function differs between parental and recombinant viruses

• Assessing whether F165R interacts with viral replication machinery that might influence recombination frequency

• Analyzing how F165R conservation or variation may impact viral fitness following recombination events

Such studies are particularly relevant given that recombinant viruses containing virulence factors from Georgia07-like genotype II ASFVs have demonstrated the ability to evade immunity induced by genotype II live attenuated vaccines .

What is the relationship between F165R and established ASFV virulence determinants?

Current research has identified several key virulence determinants in ASFV, including the MGF_505/360 gene family, the EP402R gene encoding for CD2v protein, the UK (DP96R) gene, and the 9GL gene . While F165R's precise relationship to these established virulence factors has not been fully characterized, researchers should investigate potential functional or regulatory relationships.

A systematic analytical approach would include:

This comparative framework provides a basis for hypothesis-driven research into F165R's potential contributions to ASFV virulence networks.

What expression systems yield optimal recombinant F165R production?

• Codon Optimization: Adjusting the F165R sequence for optimal codon usage in the chosen expression system.

• Expression Conditions: Optimizing temperature, induction timing, and inducer concentration to balance protein yield and solubility.

• Fusion Tags: While His-tagging has proven effective , alternative fusion partners (GST, MBP, SUMO) may enhance solubility or facilitate specific experimental applications.

• Alternative Expression Systems: For studies requiring post-translational modifications, eukaryotic systems (insect cells, mammalian cells) may be preferable, though with potentially lower yields than prokaryotic systems.

• Cell-Free Systems: For rapid small-scale production, particularly for initial characterization studies.

The optimal system should be selected based on the specific research objectives and downstream applications.

What purification and quality control protocols are recommended for recombinant F165R?

For obtaining high-purity F165R protein suitable for research applications, the following workflow is recommended:

• Initial Capture: Immobilized metal affinity chromatography (IMAC) using the N-terminal His-tag .

• Secondary Purification: Size exclusion chromatography to remove aggregates and contaminating proteins.

• Quality Control Assessments:

  • SDS-PAGE to confirm >90% purity

  • Western blotting to verify identity

  • Mass spectrometry for precise molecular weight determination

  • Dynamic light scattering to assess monodispersity

  • Circular dichroism to evaluate secondary structure integrity

• Endotoxin Removal: For applications involving cell culture or in vivo studies.

• Storage Preparation: Lyophilization in appropriate buffer conditions with 6% trehalose at pH 8.0 for stability .

These methodologies ensure consistent production of research-grade protein suitable for downstream structural and functional analyses.

What storage and handling recommendations maximize F165R stability?

To maintain optimal stability and activity of recombinant F165R protein, researchers should follow these evidence-based protocols:

• Short-term Storage: Working aliquots can be maintained at 4°C for up to one week .

• Long-term Storage: Store lyophilized protein at -20°C/-80°C upon receipt .

• Reconstitution Protocol:

  • Briefly centrifuge the vial before opening

  • Reconstitute in deionized sterile water to 0.1-1.0 mg/mL

  • Add glycerol to a final concentration of 50% for long-term storage

  • Prepare small working aliquots to avoid repeated freeze-thaw cycles

• Stability Considerations: Repeated freezing and thawing significantly reduces protein activity and should be avoided .

Following these guidelines will help ensure experimental reproducibility and maintain protein integrity throughout research projects.

What are the current knowledge gaps regarding F165R function in ASFV biology?

Despite ongoing research, several critical knowledge gaps regarding F165R remain to be addressed:

• Structural Characterization: High-resolution structural data (X-ray crystallography or cryo-EM) is needed to elucidate functional domains and potential interaction surfaces.

• Temporal Expression Profile: Understanding when during the viral life cycle F165R is expressed may provide functional insights.

• Host-Pathogen Interactions: Identification of host cell targets or binding partners remains incomplete.

• Conservation Analysis: Comprehensive comparison of F165R sequence and function across all 24 ASFV genotypes is needed .

• Contribution to Virulence: Unlike established virulence factors such as MGF_505/360, EP402R, UK, and 9GL genes, F165R's specific contribution to viral pathogenesis requires further investigation .

Addressing these gaps will require interdisciplinary approaches combining virology, structural biology, proteomics, and in vivo pathogenesis studies.

How might F165R contribute to ASFV vaccine development strategies?

The development of effective ASFV vaccines remains a global priority, and understanding F165R could contribute to this effort in several ways:

• Target for Attenuation: Similar to the UK gene and 9GL gene, which have been deleted to create attenuated ASFV vaccine candidates, F165R modification could potentially be explored as a novel attenuation strategy .

• Epitope Identification: Characterizing immunogenic regions of F165R could identify potential epitopes for subunit or vectored vaccine approaches.

• Cross-Protection Assessment: Evaluating F165R conservation across genotypes could inform predictions about cross-protection between strains, particularly relevant given the emergence of recombinant genotype I and II viruses .

• Diagnostic Target: Well-characterized F165R protein could serve as a target antigen for differentiation of infected from vaccinated animals (DIVA) diagnostic tests.

• Combinatorial Approach: Understanding how F165R interacts with other virulence factors like MGF_505/360 and EP402R could inform rational design of multi-gene deleted vaccine candidates with optimal safety and efficacy profiles .

These approaches may contribute to addressing the challenge posed by naturally occurring recombinant ASFVs that have evaded immunity induced by current experimental genotype II live vaccines .

What experimental models are most appropriate for studying F165R in the context of ASFV pathogenesis?

To effectively study F165R's role in ASFV pathogenesis, researchers should consider these experimental models:

• In Vitro Cellular Models:

  • Primary porcine macrophages (natural host cells for ASFV)

  • Stable cell lines expressing F165R to study protein-specific effects

  • 3D organoid cultures to better recapitulate tissue architecture

• Ex Vivo Systems:

  • Precision-cut lung slices from porcine tissue

  • Whole blood assays to examine interactions with immune cells

• In Vivo Models:

  • Domestic pig challenge models, examining both direct inoculation and contact transmission scenarios

  • Wild boar models to understand F165R's role in natural host species

  • Comparative studies using recombinant viruses with F165R modifications

• Computational Models:

  • Molecular dynamics simulations to predict F165R interactions

  • Transmission modeling to assess how F165R variants might impact spread

When designing in vivo experiments, researchers should note that recombinant ASFV strains have demonstrated high lethality and transmissibility, with infected pigs developing fever and succumbing to infection within 6-14 days post-inoculation or post-contact .

How does F165R variation correlate with virulence across ASFV genotypes?

Understanding the relationship between F165R sequence variation and virulence traits across ASFV genotypes requires systematic comparative analysis. Current research has identified 24 ASFV genotypes with varying degrees of virulence . While specific data on F165R variation across all genotypes is not comprehensively documented in the available research, a methodological approach would include:

• Sequence Alignment Analysis: Comparing F165R sequences across attenuated strains (like NH/P68-like genotype I viruses) and virulent strains (like Georgia07-like genotype II viruses) .

• Correlation Studies: Identifying specific amino acid positions that correlate with virulence phenotypes.

• Recombinant Virus Generation: Creating chimeric viruses where F165R from virulent strains is replaced with sequences from attenuated strains and vice versa.

• Structure-Function Analysis: Mapping sequence variations onto the protein structure to identify functional implications.

This approach would provide insights into whether F165R contributes to the differing virulence profiles observed between genotypes and how its conservation might influence cross-protection between strains.

What techniques are most effective for detecting and characterizing F165R in diagnostic samples?

For effective detection and characterization of F165R in research and diagnostic contexts, the following methodological approaches are recommended:

• Nucleic Acid-Based Detection:

  • PCR targeting F165R gene with genotype-specific primers

  • Next-generation sequencing for comprehensive genomic analysis

  • LAMP (Loop-mediated isothermal amplification) for field-applicable detection

• Protein-Based Detection:

  • Immunoassays using anti-F165R antibodies

  • Mass spectrometry for protein identification in complex samples

  • Western blotting using recombinant F165R as a positive control

• Functional Characterization:

  • Activity assays (once specific enzymatic activity is identified)

  • Binding assays to identify interaction partners

  • Cellular localization studies using fluorescently tagged proteins

These techniques should be validated using recombinant F165R protein standards of known purity to ensure accurate detection and characterization in experimental and field samples.