Phylogenetic distribution of DNA topoisomerase VI and its distinction from SPO11.

DNA topoisomerases (topos) are major targets for antimicrobial and chemotherapeutic drugs due to their fundamental roles in regulating DNA topology. Type II topos are essential for chromosome segregation and relaxing positive DNA supercoils, and are exemplified by topo II in eukaryotes, topo IV and DNA gyrase in bacteria, and topo VI in archaea. Topo VI occurs ubiquitously in plants and sporadically in bacteria, algae, and other protists and is highly homologous to Spo11, which initiates eukaryotic homologous recombination. This homology makes the two complexes difficult to distinguish by sequence and leads to discrepancies such as the identity of the putative topo VI in malarial species. A lack of understanding of the role and distribution of topo VI outside of archaea hampers its pursuit as a potential drug target, and the present study addresses this with an up-to-date and extensive phylogenetic analysis. We show that the A and B subunits of topo VI and Spo11 can be distinguished using phylogenetics and structural modelling, and that topo VI is not present in nor other members of the phylum Apicomplexa. These findings provide insights into the evolutionary relationships between topo VI and Spo11, and their adoption alongside other type II topos.