Cryo-EM structures of African swine fever virus topoisomerase

Type II topoisomerases ubiquitously exist in cellular organisms, where they play an essential role in resolving the topological problems of DNA. The viral type II topoisomerase encoded by the African swine fever virus (ASFV) is critical for viral replication and infection, thus representing an attractive target for antiviral drug development. Here we report two cryo-EM structures of ASFV topoisomerase P1192R in distinct conformations at an overall resolution of 3.16 angstrom and 3.13 angstrom, respectively. P1192R assembles as a homodimer with the C-gate formed by the coiled-coil domain adopting a closed or open conformation before reaction, providing the first visual evidence for the dynamic motions of the C-gate of type II topoisomerase. Comparative structural comparisons of eukaryotic homologs and P1192R reveal the unique structural features of P1192R, including the active site configuration, a flexible loop in the TOPRIM domain, an additionally inserted a-helix in the tower domain, and a pin-like structure in the C-terminal coiled-coil domain, which are important for enzyme activity and protein folding. These findings provide important insights into the structure and function of viral topoisomerases and may guide the efficient development of anti-ASFV drugs. Moreover, our study also offers structural evidence to support the scenario of the viral origin of eukaryotic type IIA topoisomerases. IMPORTANCE African swine fever virus (ASFV) is a highly contagious virus that causes lethal hemorrhagic diseases known as African swine fever (ASF) with a case fatality rate of 100%. There is an urgent need to develop anti-ASFV drugs. We determine the first high-resolution structures of viral topoisomerase ASFV P1192R in both the closed and open C-gate forms. P1192R shows a similar overall architecture with eukaryotic and prokaryotic type II topoisomerases, which have been successful targets of many antimicrobials and anticancer drugs, with the most similarity to yeast topo II. P1192R also exhibits differences in the details of active site configuration, which are important to enzyme activity. These two structures offer useful structural information for antiviral drug design and provide structural evidence to support that eukaryotic type IIA topoisomerase likely originated from horizontal gene transfer from the virus.