African swine fever virus pA104R protein acts as a suppressor of type I interferon signaling

Thonningianin A disrupts pA104R-DNA binding and inhibits African swine fever virus replication

African swine fever is a highly lethal disease caused by the African swine fever virus (ASFV), posing a significant threat to the global pig industry, wherease no approved treatments are currently available. The ASFV DNA-binding protein, pA104R, plays a critical role in viral genome packaging and replication, making it a key target for drug discovery. Through structure-based virtual screening, we identified a polyphenolic compound, thonningianin A, which disrupts the pA104R-DNA binding and significantly inhibits ASFV replication. Mechanistic study revealed that thonningianin A binds to the DNA-binding region of pA104R, forming strong hydrogen bonds with H100 and occupying the vital DNA-binding residues K92, R94, and K97. In addition, we resolved the high-resolution (1.8 Å) structure of pA104R (PDB ID 9JS5), providing valuable insights for future drug screening. Together, these results demonstrate that thonningianin A holds great potential for the development of anti-ASFV drug, as a herb extract with favourable pharmacokinetic properties and safety.

Advances in African swine fever virus molecular biology and host interactions contributing to new tools for control

African swine fever virus (ASFV) causes a frequently fatal hemorrhagic disease in domestic pigs and wild boar. The spread from Africa to Georgia in 2007 initiated a pandemic affecting many European and most Asian countries. This has had a very high socio-economic impact and threatens global food security. The virus is a large, complex, cytoplasmic DNA virus, the only member of the Asfarviridae family and codes for 170-190 proteins. Many of these have unknown functions and do not resemble other viruses or host proteins. This complexity has hindered the development of vaccines and other tools for control. The intensity of research has increased since the spread of ASFV in Europe and Asia, leading to rapid advances in knowledge. This review summarizes recent research, including the determination by cryogenic electron microscopy of the virus capsid structure and virion proteome. Novel information on the virus replication cycle, including mechanisms of virus entry into cells and the identification of host endosomal proteins important for entry, is summarized. Multiple, novel virus immune evasion proteins and their targets in the type I interferon response and inflammation pathways have been identified. The potential for the application of this knowledge to developing novel control tools, including modified live vaccines and other interventions targeting critical virus processes or host interactions, is discussed.

Inhibition of STING-mediated type I IFN signaling by African swine fever virus DP71L

African swine fever virus (ASFV) is nucleocytoplasmic large DNA arbovirus and encodes many proteins involved in the interaction with host molecules to evade antiviral immune responses. Especially, evasion strategies of type I interferon (IFN-I)-mediated immune responses are crucial for early ASFV replication. However, there is still a lack of information regarding the immune evasion mechanism of ASFV proteins. Here, we demonstrated that ASFV DP71L suppresses STING-mediated antiviral responses. The conserved phosphatase 1 (PP1) motif of DP71L specifically interact with the C-terminal tail (CTT) of STING and in particular, amino acids P371, L374, and R375 of STING were important for interaction with DP71L. Consequently, this interaction disrupted the binding between STING and TANK-binding kinase 1 (TBK1), thereby inhibiting downstream signaling including phosphorylation of TBK1, STING and IRF3 for antiviral signaling. DP71L significantly interfered with viral DNA induced interferon production and IFN-mediated downstream signaling in vitro. Consistently, knockdown of DP71L enhanced antiviral gene expression in ASFV-infected cells. Taken together, these results highlight the important role of DP71L with respect to inhibition of interferon responses and provide guidance for a better understanding of ASFV pathogenesis and the development of live attenuated ASFV vaccines.

Comprehensive Characterization of the Genetic Landscape of African Swine Fever Virus: Insights into Infection Dynamics, Immunomodulation, Virulence and Genes with Unknown Function

African Swine Fever (ASF) is a lethal contagious hemorrhagic viral disease affecting the swine population. The causative agent is African Swine Fever Virus (ASFV). There is no treatment or commercial vaccine available at present. This virus poses a significant threat to the global swine industry and economy, with 100% mortality rate in acute cases. ASFV transmission occurs through both direct and indirect contact, with control measures limited to early detection, isolation, and culling of infected pigs. ASFV exhibits a complex genomic structure and encodes for more than 50 structural and 100 non-structural proteins and has 150 to 167 open reading frames (ORFs). While many of the proteins are non-essential for viral replication, they play crucial roles in mediating with the host to ensure longevity and transmission of virus in the host. The dynamic nature of ASFV research necessitates constant updates, with ongoing exploration of various genes and their functions, vaccine development, and other ASF-related domains. This comprehensive review aims to elucidate the structural and functional roles of both newly discovered and previously recorded genes involved in distinct stages of ASFV infection and immunomodulation. Additionally, the review discusses the virulence genes and genes with unknown functions, and proposes future interventions.

Characterization of the monoclonal antibody and the immunodominant B-cell epitope of African swine fever virus pA104R by using mouse model

The African swine fever virus (ASFV) structural protein pA104R is the only histone-like protein encoded by eukaryotic viruses. pA104R is an essential DNA-binding protein required for DNA replication and genome packaging of ASFV, which are vital for pathogen survival and proliferation. pA104R is an important target molecule for diagnosing, treating, and immune prevention of ASFV. This study characterized monoclonal antibodies (mAbs) against pA104R and found them to recognize natural pA104R in ASFV strains with different genotypes, showing high conservation. Confirmation analyses of pA104R epitopes using mAbs indicated the presence of immunodominant B-cell epitopes, and further characterization showed the high antigenic index and surface accessibility coefficients of the identified epitope. Furthermore, the pA104R protein functions through the polar interactions between the binding amino acid sites; however, these interactions may be blocked by the recognition of generated mAbs. Characterizing the immunodominant B-cell epitope of the ASFV critical proteins, such as pA104R, may contribute to developing sensitive diagnostic tools and vaccine candidate targets.IMPORTANCEAfrican swine fever (ASF) is a highly pathogenic, lethal, and contagious viral disease affecting domestic pigs and wild boars. As no effective vaccine or other treatments have been developed, the control of African swine fever virus (ASFV) relies heavily on virus detection and diagnosis. A potential serological target is the structural protein pA104R. However, the molecular basis of pA104R antigenicity remains unclear, and a specific monoclonal antibody (mAb) against this protein is still unavailable. In this study, mAbs against pA104R were characterized and found to recognize natural pA104R in ASFV strains with different genotypes. In addition, confirmation analyses of pA104R epitopes using mAbs indicated the presence of immunodominant B-cell epitopes, and further characterization showed the high antigenic index and surface accessibility coefficients of the identified epitope. Characteristics of the immunodominant B-cell epitope of ASFV proteins, such as pA104R, may contribute to developing sensitive diagnostic tools and identifying vaccine candidate targets.

Interactome between ASFV and host immune pathway proteins

IMPORTANCE

African swine fever (ASF), caused by African swine fever virus (ASFV), has become a major crisis for the pork industry in recent years. The mechanism for ASFV pathology and the clinical symptoms difference of ASF between domestic pigs and reservoir hosts remain to be elucidated. We deciphered the comprehensive protein-protein interaction (PPI) network between ASFV and host immune pathways. The intensive PPI network contained both ASFV-host immune pathway PPI and ASFV-ASFV PPI information, providing a comprehensive ASFV-host interaction landscape. Furthermore, the ASFV-host PPI difference between domestic pigs and warthogs was explored, which will be instructive for exploring essential candidates involved in ASFV pathology. Moreover, we screened the inhibitory effect of ASFV proteins in the PPI with cGAS-STING pathway on IFN-I and NF-κB, further providing possible functions of ASFV-host PPI network in innate immune regulation.