Recombinant African swine fever virus Uncharacterized protein F165R (Ken-058)

What is the F165R protein in African swine fever virus?

F165R is an uncharacterized protein encoded by the African swine fever virus genome. Based on transcriptome mapping studies, F165R is located on the positive strand of the ASFV genome with a primary transcription start site (pTSS) coordinate at position 42354 and a corrected start at position 42359. The open reading frame (ORF) encodes a 136 amino acid protein, though there is an alternative ATG codon 63 nucleotides downstream of the primary start site that could potentially result in a shorter protein isoform . As an uncharacterized protein, the exact function of F165R in viral replication and pathogenesis remains to be fully elucidated through ongoing research efforts.

What expression pattern does F165R exhibit during ASFV infection?

While the search results don't specifically categorize F165R as an early or late gene, we can examine the gene expression patterns of ASFV generally. ASFV genes show differential expression during the viral replication cycle, with distinct early and late gene sets. Transcriptome analysis using CAGE-seq has identified that the majority of multigene family (MGF) genes are expressed early in infection, with the exception of MGF 505-2R, MGF 360-2L, and MGF 100-1L . The specific temporal expression pattern of F165R would need to be confirmed experimentally, possibly through time-course studies with techniques like CAGE-seq or RNA-seq that can detect transcription start sites and expression levels at different stages of infection.

How is recombinant F165R protein typically produced for research applications?

Recombinant F165R protein for research applications is typically produced using bacterial expression systems, particularly in Escherichia coli. According to the available information, recombinant ASFV F165R protein can be expressed as amino acids 1-165 in E. coli systems . The production process generally involves:

• Cloning the F165R gene sequence into an appropriate expression vector

• Transforming the construct into a suitable E. coli strain

• Inducing protein expression under optimized conditions

• Purifying the recombinant protein using appropriate chromatography techniques

• Verifying protein identity and purity through methods such as SDS-PAGE and Western blotting

The resulting recombinant protein can then be used for various research applications, including antibody production, protein-protein interaction studies, and functional characterization assays. It's important to note that these products are strictly for research purposes and cannot be used directly on humans or animals .

What methodologies are most effective for determining the function of uncharacterized proteins like F165R in ASFV?

Determining the function of uncharacterized viral proteins requires a multi-faceted approach combining both computational and experimental methodologies:

• Bioinformatic analysis: Sequence homology searches, structural prediction, and motif identification can provide initial insights into potential functions. For proteins like F165R with limited homology to known proteins, more sophisticated approaches such as protein fold recognition and ab initio structure prediction may be necessary.

• Gene knockout/knockdown studies: Creating recombinant ASFV strains with F165R deletions or mutations can reveal the protein's role in viral replication and pathogenesis. Recent advances in ASFV reverse genetics systems, including synthetic genomics-based approaches, have made it possible to generate recombinant ASFV strains with specific genetic modifications .

• Protein-protein interaction studies: Techniques such as yeast two-hybrid, co-immunoprecipitation, or proximity labeling approaches can identify viral or host proteins that interact with F165R, providing clues to its function.

• Subcellular localization: Immunofluorescence microscopy or biochemical fractionation studies with tagged versions of F165R can determine where the protein localizes during infection, suggesting potential roles.

• Functional assays: Based on preliminary data, specific assays can be designed to test hypothesized functions, such as effects on host immune response, viral replication, or structural roles.

• Transcriptomics and proteomics: Comparing gene and protein expression patterns between wild-type virus and F165R mutants can reveal affected pathways.

The integration of these approaches provides the most robust strategy for functionally characterizing previously uncharacterized viral proteins like F165R.

How do transcription start site variations affect F165R protein expression and function?

Transcription start site variations can significantly impact protein expression and function through multiple mechanisms. For F165R specifically, genome-wide transcriptome mapping has identified its primary transcription start site (pTSS) at position 42354, with a corrected start at 42359. Importantly, an alternative ATG codon has been noted 63 nucleotides downstream of the primary start site .

This alternative start codon could lead to the production of a truncated protein isoform with potentially distinct functional properties. The variations in transcription start sites can affect:

• Protein sequence and structure: A protein initiating at the alternative ATG would lack approximately 21 N-terminal amino acids compared to the full-length protein, potentially affecting protein folding, stability, or function.

• Regulatory elements in mRNA: Alternative transcription start sites generate mRNAs with different 5' untranslated regions (UTRs), which can contain regulatory elements affecting translation efficiency, mRNA stability, or localization.

• Temporal regulation: Different transcription start sites might be preferentially utilized during different stages of infection (early vs. late), allowing for temporal control of protein isoform expression.

• Subcellular targeting: N-terminal sequences often contain targeting signals; truncated variants may localize to different cellular compartments.

Experimentally addressing these questions would require techniques such as 5' RACE to confirm transcription start sites, ribosome profiling to identify translation start sites, and functional characterization of the different protein isoforms through targeted mutagenesis and expression studies.

What role might F165R play in ASFV virulence and host immune evasion?

While the specific role of F165R in ASFV virulence has not been directly established based on the provided search results, we can propose potential functions based on what is known about other ASFV virulence factors and uncharacterized proteins:

• Immune modulation: Many ASFV proteins function to suppress or evade host immune responses. F165R could potentially interfere with host signaling pathways, cytokine production, or antigen presentation.

• Viral replication complex: Some uncharacterized viral proteins serve as components of viral replication or transcription complexes. F165R might play a structural or regulatory role in these processes.

• Host range determination: ASFV contains multiple multigene families (MGFs) that are often associated with host range and virulence. Although F165R is not explicitly identified as part of these families in the search results, it could function similarly in determining viral tropism or host adaptation.

To experimentally investigate its role in virulence:

• Generate recombinant ASFV strains with F165R deletions or mutations using reverse genetics approaches .

• Compare growth kinetics and cytopathic effects of wild-type and mutant viruses in relevant cell types.

• Analyze host transcriptional responses to wild-type versus F165R-mutant viruses using RNA-seq.

• Conduct in vivo experiments with appropriate animal models to assess virulence attenuation.

• Perform immunological assays to determine effects on specific immune pathways.

This systematic approach would help elucidate the potential contribution of F165R to ASFV virulence and host immune evasion strategies.

How can recombinant F165R be used in diagnostic applications for ASFV detection?

Recombinant F165R protein has potential applications in developing diagnostic tools for ASFV detection, particularly in serological assays. A methodological approach to developing F165R-based diagnostics would include:

• Production of high-quality recombinant protein: Express and purify recombinant F165R with high yield and purity, ensuring proper folding to maintain antigenic epitopes. E. coli expression systems have been successfully used for producing recombinant ASFV proteins, including F165R .

• Antibody development:

  • Generate polyclonal antibodies by immunizing laboratory animals with purified recombinant F165R

  • Develop monoclonal antibodies through hybridoma technology for increased specificity

  • Validate antibody specificity against various ASFV isolates and screen for cross-reactivity

• ELISA development:

  • Design indirect ELISAs using recombinant F165R as the capture antigen to detect anti-ASFV antibodies in pig serum

  • Develop competitive ELISAs where F165R-specific antibodies compete with serum antibodies

  • Optimize assay conditions including coating concentration, blocking agents, and detection systems

• Evaluation and validation:

  • Determine diagnostic sensitivity and specificity using well-characterized serum panels

  • Compare performance against gold standard methods and other established ASFV diagnostic assays

  • Conduct field validation studies in different geographical regions with diverse ASFV isolates

• Implementation considerations:

  • Assess the stability of F165R in various storage conditions

  • Evaluate lot-to-lot consistency in manufacturing

  • Develop standardized protocols for different laboratory settings

The potential advantage of F165R-based diagnostics would need to be experimentally compared to existing diagnostic targets such as p72 (B646L) or p30 (CP204L), which are currently widely used in ASFV diagnostics.

What are the optimal conditions for expressing and purifying recombinant F165R protein?

The optimal conditions for expressing and purifying recombinant F165R protein would involve a systematic optimization approach:

• Expression vector selection:

  • Choose vectors with strong, inducible promoters (T7, tac) for controlled expression

  • Consider fusion tags (His, GST, MBP) to facilitate purification and potentially enhance solubility

  • For F165R specifically, N-terminal tags may be preferable since there's an alternative ATG codon 63 nucleotides downstream

• Expression host optimization:

  • Standard E. coli strains (BL21(DE3), Rosetta) have been successfully used for ASFV proteins

  • For potentially toxic viral proteins, consider strains with tighter expression control

  • Codon optimization may improve expression, particularly for regions with rare codons

• Expression conditions:

  • Temperature: Lower temperatures (16-25°C) often improve folding and solubility

  • Induction: Test various IPTG concentrations (0.1-1.0 mM) and induction times (4-24 hours)

  • Media composition: Rich media (2xYT, TB) versus minimal media depending on downstream applications

  • Consider additives that might enhance solubility (sorbitol, glycerol, low concentrations of non-ionic detergents)

• Purification strategy:

  • For His-tagged F165R: IMAC (immobilized metal affinity chromatography)

  • For GST-tagged F165R: Glutathione affinity chromatography

  • Secondary purification: Ion exchange chromatography based on F165R's predicted isoelectric point

  • Final polishing: Size exclusion chromatography to ensure monodispersity

• Protein quality assessment:

  • SDS-PAGE and Western blotting to confirm identity and purity

  • Mass spectrometry for accurate molecular weight determination

  • Circular dichroism to assess secondary structure content

  • Dynamic light scattering to evaluate homogeneity

Each step would require empirical optimization, as the behavior of uncharacterized proteins like F165R can be difficult to predict based on sequence information alone. The final protocol should be determined based on the specific downstream applications for the purified protein.

What are the challenges in developing a recombinant ASFV with F165R modifications for functional studies?

Developing recombinant ASFV with F165R modifications presents several technical challenges that researchers must address:

• Lack of efficient reverse genetics systems:

  • Traditional homologous recombination approaches in ASFV have low efficiency

  • Recent synthetic genomics-based approaches offer promise but are technically demanding

  • The need for specialized facilities and expertise limits widespread adoption

• Genome size and complexity:

  • The large ASFV genome (~170-190 kb) complicates genetic manipulation

  • Repetitive sequences and complex genomic structure can lead to unwanted recombination events

  • Maintaining genome stability during manipulation is challenging

• Cell culture limitations:

  • ASFV primarily replicates in primary macrophages, which are heterogeneous and difficult to transfect

  • Adaptation to continuous cell lines often results in genetic modifications that can confound results

  • Development of permissive cell lines expressing helper functions may be necessary

• Potential lethality of modifications:

  • If F165R is essential for viral replication, direct knockout approaches may not yield viable virus

  • Conditional expression systems or partial modifications may be necessary

  • Complementing cell lines may be required to propagate defective viruses

• Phenotypic verification methods:

  • Distinguishing effects of F165R modification from other spontaneous mutations

  • Developing appropriate assays to detect potentially subtle phenotypic changes

  • Ensuring that tagged versions of F165R retain native functionality

• Biosafety considerations:

  • Work with ASFV requires appropriate biosafety level facilities

  • Risk assessment for recombinant ASFV strains

  • Regulatory approvals and containment measures

Recent advances that could help overcome these challenges include the development of synthetic genomics approaches for ASFV , CRISPR-Cas9 technology for more efficient genome editing, and the identification of cell lines that can better support ASFV replication. Researchers should consider combinatorial approaches, using in vitro systems to complement in vivo studies with recombinant viruses.

How can transcriptomic approaches be applied to study F165R expression during ASFV infection?

Transcriptomic approaches offer powerful tools for studying F165R expression dynamics during ASFV infection. A comprehensive methodological strategy would include:

• Time-course experimental design:

  • Infect appropriate cells (porcine macrophages or adapted cell lines) with ASFV

  • Collect samples at multiple timepoints covering early (2-6h), intermediate (8-12h), and late (16-24h) infection stages

  • Include mock-infected controls and appropriate biological replicates

  • Consider synchronizing infection using temperature shifts or specific inhibitors

• RNA-seq for global transcriptome analysis:

  • Total RNA extraction with protocols preserving RNA integrity

  • Ribosomal RNA depletion to enrich for mRNA

  • Library preparation with strand-specific protocols

  • Deep sequencing (minimum 30M reads per sample) for adequate coverage of viral transcripts

  • Measure F165R expression relative to other viral and host genes

• CAGE-seq for transcription start site identification:

  • Specifically captures 5' capped RNA, identifying transcription start sites at single-nucleotide resolution

  • Can confirm the previously identified F165R pTSS at position 42354 and potential alternative start sites

  • Differential CAGE-seq analysis between timepoints reveals temporal regulation patterns

• Targeted approaches for validation:

  • RT-qPCR with primers specific to F165R for sensitive quantification

  • 5' RACE to confirm transcription start sites identified by CAGE-seq

  • Northern blotting to visualize transcript size and potential processing

• Integration with proteomics:

  • Parallel proteomics analysis to correlate transcript and protein levels

  • Ribosome profiling to identify actively translated regions of F165R transcripts

  • Correlation between transcriptional and translational regulation

• Data analysis framework:

  • Specialized bioinformatics pipelines for mapping reads to the ASFV genome

  • Differential expression analysis between timepoints

  • Clustering of co-expressed genes to identify regulatory modules

  • Integration with existing ASFV transcriptome datasets

This comprehensive approach would provide detailed insights into F165R expression dynamics, potential alternative transcripts, and its regulation within the context of the viral infection cycle. Based on existing transcriptome studies, special attention should be paid to the early vs. late infection transition, as ASFV shows distinct temporal regulation patterns .

How does F165R vary across different ASFV isolates and what are the functional implications?

Understanding the sequence variation of F165R across different ASFV isolates is crucial for determining its potential role in virulence, host adaptation, and developing broadly effective countermeasures. A methodological approach to this comparative analysis would include:

The analysis should particularly focus on differences between highly virulent isolates (like Georgia 2007/1) and attenuated isolates or related viruses with different host ranges, as these comparisons may provide insights into F165R's potential role in virulence or host adaptation.

How does F165R compare to other uncharacterized proteins in the ASFV genome in terms of conservation and expression patterns?

• Genome-wide conservation analysis:

  • Calculate sequence conservation scores for all ASFV proteins across multiple isolates

  • Create a ranked list of proteins based on conservation levels

  • Position F165R within this conservation spectrum

  • Group proteins into highly conserved, moderately conserved, and highly variable categories

  • Examine if conservation patterns correlate with known or predicted functions

• Expression pattern comparison:

  • Analyze transcriptomic data to classify all ASFV genes into temporal expression categories (early, intermediate, late)

  • Create expression profiles for each uncharacterized protein across the infection time course

  • Cluster proteins with similar expression patterns, identifying which cluster contains F165R

  • Determine if F165R expression correlates with genes of known function

• Comparative promoter analysis:

  • Extract and align promoter regions of ASFV genes, including F165R

  • Identify common motifs associated with early, intermediate, or late expression

  • Compare the F165R promoter structure with those of other uncharacterized proteins

  • Correlate promoter features with observed expression patterns

• Structural features comparison:

  • Predict structural features (secondary structure, disorder regions, transmembrane domains) for all uncharacterized proteins

  • Group proteins with similar predicted structural characteristics

  • Identify any unique structural features of F165R compared to other uncharacterized proteins

• Protein interaction network prediction:

  • Use computational approaches to predict protein-protein interactions

  • Position F165R within the predicted ASFV interactome

  • Identify uncharacterized proteins predicted to interact with similar partners as F165R

What are the key knowledge gaps surrounding F165R and how should future research be prioritized?

Despite advances in ASFV research, significant knowledge gaps remain regarding F165R. These gaps and suggested research priorities include:

• Functional characterization:

  • The primary function of F165R remains unknown

  • Priority: Develop gene knockout/knockdown approaches and assess effects on viral replication, virulence, and host responses

  • Apply proteomics approaches to identify interaction partners that may suggest functional roles

• Structural information:

  • No experimental structural data exists for F165R

  • Priority: Determine the three-dimensional structure through X-ray crystallography, cryo-EM, or NMR spectroscopy

  • Structural information would provide insights into potential functions and facilitate drug design efforts

• Temporal regulation:

  • While transcriptomic studies have categorized many ASFV genes as early or late, specific data on F165R temporal expression patterns requires clarification

  • Priority: Conduct time-course studies with quantitative approaches to definitively establish F165R's expression pattern

• Cross-isolate variation:

  • Limited information exists on F165R sequence conservation across diverse ASFV isolates

  • Priority: Comparative genomic analysis of F165R across multiple genotypes to identify conserved functional domains and variable regions

• Immunological relevance:

  • Unknown whether F165R elicits immune responses during infection or vaccination

  • Priority: Evaluate immunogenicity in natural infection and determine if antibodies against F165R correlate with protection

• Role in virulence:

  • Potential contribution to ASFV virulence has not been established

  • Priority: Generate and characterize F165R mutant viruses and assess virulence in appropriate models

Prioritization of these research directions should consider both the fundamental biological understanding of ASFV and the potential applications for diagnosis, vaccine development, and antiviral strategies. Given the challenges in ASFV research, collaborative approaches leveraging complementary expertise and resources will be most effective in addressing these knowledge gaps.

How might F165R be utilized in next-generation ASFV vaccine development strategies?

F165R could potentially contribute to next-generation ASFV vaccine development through several methodological approaches:

• Subunit vaccine component:

  • Recombinant F165R could be included in subunit vaccine formulations

  • Methodology: Express and purify F165R, possibly in combination with other immunogenic ASFV proteins

  • Evaluate different adjuvant combinations to enhance immune responses

  • Test prime-boost strategies with varied delivery platforms (protein, viral vectors, DNA)

  • Systematically assess protective efficacy against challenge with virulent ASFV strains

• Target for live-attenuated vaccine development:

  • If F165R contributes to virulence, its modification could generate attenuated vaccine candidates

  • Methodology: Create recombinant ASFV with F165R deletions or mutations using reverse genetics approaches

  • Characterize attenuation in vitro and in vivo

  • Evaluate safety, immunogenicity, and protective efficacy in swine models

  • Ensure genetic stability of the attenuated phenotype

• Marker for differentiating infected from vaccinated animals (DIVA):

  • If F165R elicits consistent antibody responses during infection, it could serve as a DIVA marker

  • Methodology: Develop F165R-based serological assays

  • Design vaccines that exclude or modify F165R epitopes

  • Validate DIVA capability using serum panels from infected and vaccinated animals

• Vectored vaccine development:

  • F165R could be expressed in viral vectors (adenovirus, modified vaccinia Ankara)

  • Methodology: Generate recombinant vectors expressing F165R

  • Optimize expression levels and potential modifications for enhanced immunogenicity

  • Evaluate cellular and humoral immune responses

  • Test protection against ASFV challenge

• mRNA vaccine platform:

  • F165R-encoding mRNA could be included in lipid nanoparticle formulations

  • Methodology: Design and synthesize optimized mRNA constructs

  • Formulate with appropriate delivery systems

  • Assess protein expression, immunogenicity, and protective efficacy

The development of ASFV vaccines has been challenging due to the complex nature of the virus and immunity. Successful approaches will likely involve rational design based on understanding the functions of viral proteins like F165R, along with comprehensive immunological evaluation. The recent advances in reverse genetics systems for ASFV provide new opportunities to systematically evaluate the role of F165R in protection and its potential as a vaccine component.

What specialized techniques and tools are recommended for studying ASFV F165R protein interactions?

Investigating protein interactions of uncharacterized viral proteins like F165R requires a multi-faceted approach combining complementary techniques:

• Affinity purification-mass spectrometry (AP-MS):

  • Express tagged F165R (e.g., FLAG, HA, or His) in relevant cell systems

  • Perform pull-downs under physiologically relevant conditions

  • Identify interacting partners by mass spectrometry

  • Validate key interactions with orthogonal methods

  • Compare interaction profiles between different cell types and infection stages

• Proximity labeling approaches:

  • Generate fusion proteins with BioID, TurboID, or APEX2 enzymes

  • Express in infected cells or alongside other viral proteins

  • Identify proximal proteins through biotinylation and streptavidin pulldown

  • Advantages: Captures transient and weak interactions in native cellular environments

• Yeast two-hybrid (Y2H) screening:

  • Construct F165R bait plasmids

  • Screen against prey libraries derived from porcine cells or ASFV orfeome

  • Validate positive interactions through directed Y2H and co-immunoprecipitation

  • Best for detecting direct binary interactions

• Protein complementation assays:

  • Split reporter systems (BiFC, NanoBiT, split-luciferase)

  • Allow monitoring of protein interactions in live cells

  • Enable spatial and temporal resolution of interactions during infection

• Cross-linking mass spectrometry (XL-MS):

  • Apply protein crosslinkers to infected cells or purified complexes

  • Identify interaction interfaces at amino acid resolution

  • Provides structural constraints for modeling protein complexes

• Co-localization studies:

  • Fluorescently tag F165R and candidate interacting partners

  • Perform confocal or super-resolution microscopy

  • Track co-localization during different stages of viral infection

  • Consider FRET or FLIM approaches for direct interaction evidence

• Protein arrays:

  • Test F165R binding against arrays of host proteins

  • Useful for screening numerous potential interactions simultaneously

  • Identify unexpected interaction partners from diverse cellular pathways

Each technique has distinct strengths and limitations, making a combined approach most effective. Particular attention should be paid to control experiments, including the use of unrelated viral or cellular proteins as specificity controls, and validation across multiple experimental systems. Current ASFV research suggests that viral proteins often target host immune pathways , making these proteins particularly interesting candidates for interaction studies with F165R.

What bioinformatic resources and databases are most valuable for analyzing F165R and related ASFV proteins?

Researchers studying F165R and other ASFV proteins can leverage numerous bioinformatic resources to generate hypotheses and guide experimental work. A comprehensive toolkit would include:

• Sequence databases and genome browsers:

  • NCBI Virus (https://www.ncbi.nlm.nih.gov/labs/virus/): Repository of viral genome sequences including ASFV isolates

  • UniProt (https://www.uniprot.org): Provides annotated protein sequences and functional information; contains entries for F165R proteins

  • ASFVdb: Specialized database for ASFV genomics and proteomics

• Sequence analysis tools:

  • BLAST/PSI-BLAST: For identifying distant homologs of F165R

  • HMMER: Profile-based searches that may detect remote homologies missed by BLAST

  • Multiple sequence alignment tools (MUSCLE, MAFFT, Clustal Omega): For comparative analysis of F165R across isolates

  • Jalview: Visualization and analysis of sequence alignments

• Structural prediction resources:

  • AlphaFold2/RoseTTAFold: State-of-the-art protein structure prediction

  • I-TASSER: Integrated platform for structure and function prediction

  • PredictProtein: Suite of tools for secondary structure and functional site prediction

  • TMHMM/TOPCONS: Transmembrane domain prediction

  • SignalP: Signal peptide prediction

• Functional annotation tools:

  • InterProScan: Integrated search against multiple protein signature databases

  • Pfam: Protein domain identification

  • PROSITE: Detection of functionally significant sites and patterns

  • NetPhos: Phosphorylation site prediction

  • SUMOplot: Sumoylation site prediction

• Transcriptomics databases and tools:

  • NCBI GEO/SRA: Repositories containing ASFV transcriptome datasets

  • ASFV Transcriptome Viewer: Specialized tool for exploring ASFV gene expression

  • DESeq2/edgeR: Tools for analyzing differential expression

• Protein-protein interaction prediction:

  • STRING: Database of known and predicted protein interactions

  • PSICQUIC: Framework for accessing molecular interaction databases

  • Interologous Interaction Database (I2D): Prediction of interactions based on orthologs

• Specialized viral bioinformatics resources:

  • ViralZone: Knowledge resource for viral biology

  • Virus Pathogen Resource (ViPR): Integrated repository of data and analysis tools

  • Viral Bioinformatics Resource Center: Tools for viral genome analysis

• Phylogenetic analysis tools:

  • MEGA: Molecular evolutionary genetics analysis software

  • RAxML/IQ-TREE: Maximum likelihood phylogenetic tree construction

  • FigTree: Visualization and editing of phylogenetic trees

When using these resources for F165R analysis, researchers should consider the following best practices:

• Combine multiple prediction methods and look for consensus

• Pay attention to confidence scores and statistical significance

• Validate bioinformatic predictions with experimental approaches

• Use ASFV-specific resources when available, as they incorporate domain knowledge about this unique virus family

These resources can provide valuable insights into potential functions, structural features, and evolutionary relationships of F165R, guiding targeted experimental investigations.