Structural insights into the DNA topoisomerase II of the African swine fever virus

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.

Virtual Screening and Molecular Dynamics Simulation Targeting the ATP Domain of African Swine Fever Virus Type II DNA Topoisomerase

African Swine Fever Virus (ASFV) Topo II ATPase domain, resistant to conventional inhibitors (e.g., ICRF-187) due to M18/W19 steric clashes, was targeted via hierarchical virtual screening (Schrödinger) of the Chembridge library combined with MM/GBSA calculations. Five ligands (10012949, 40242484, 46712145, 15880207, and 33688815) showed high affinity, with 46712145 adopting symmetrical π-π stacking, hydrogen bonds, and alkyl interactions to bypass steric hindrance. Molecular dynamics simulations (100 ns) revealed ligand-induced flexibility, evidenced by elevated RMSD/Rg values versus the free protein. DCCM analysis highlighted enhanced anti-correlated motions between GHKL motifs and sensor domains in chain B/C, suggesting stabilization of a non-catalytic conformation to inhibit ATP hydrolysis. Free energy landscape (FEL) analysis showed 46712145 occupying a broad, shallow energy basin, enabling conformational adaptability, contrasting the narrow deep well of the free protein. This study proposes a symmetric ligand design strategy and conformational capture mechanism to block ATPase activity. Compound 46712145 demonstrates stable binding and dynamic regulation, providing a novel lead scaffold for anti-ASFV drug development. These findings establish a structural framework for combating ASFV through targeted ATPase inhibition.

Structural and functional insights into the T-even type bacteriophage topoisomerase II

T-even type bacteriophages are virulent phages commonly used as model organisms, playing a crucial role in understanding various biological processes. One such process involves the regulation of DNA topology during phage replication upon host infection, governed by type IIA DNA topoisomerases. In spite of various studies on prokaryotic and eukaryotic counterparts, viral topoisomerase II remains insufficiently understood, especially the unique domain composition of T4 phage. In this study, we determine the cryo-EM structures of topoisomerase II from T4 and T6 phages, including full-length structures of both apo and DNA-binding states which have never been determined before. Together with other conformational states, these structures provide an explicit blueprint of mechanisms of phage topoisomerase II. Particularly, the asymmetric dimeric interactions observed in cryo-EM structures of T6 phage topoisomerase II ATPase domain and central domain bound with DNA shed light on the asynchronous ATP usage and asynchronous cleavage of the G-segment DNA, respectively. The elucidation of phage topoisomerase II's structures and functions not only enhances our understanding of mechanisms and evolutionary parallels with prokaryotic and eukaryotic homologs but also highlights its potential as a model for developing type IIA topoisomerase inhibitors.