Topoisomerase VI is a chirally-selective, preferential DNA decatenase

DNA topoisomerase VI (topo VI) is a type IIB DNA topoisomerase found predominantly in archaea and some bacteria, but also in plants and algae. Since its discovery, topo VI has been proposed to be a DNA decatenase; however, robust evidence and a mechanism for its preferential decatenation activity was lacking. Using single-molecule magnetic tweezers measurements and supporting ensemble biochemistry, we demonstrate that Methanosarcina mazei topo VI preferentially unlinks, or decatenates DNA crossings, in comparison to relaxing supercoils, through a preference for certain DNA crossing geometries. In addition, topo VI demonstrates a significant increase in ATPase activity, DNA binding and rate of strand passage, with increasing DNA writhe, providing further evidence that topo VI is a DNA crossing sensor. Our study strongly suggests that topo VI has evolved an intrinsic preference for the unknotting and decatenation of interlinked chromosomes by sensing and preferentially unlinking DNA crossings with geometries close to 90 degrees.

Automated summary

DNA topoisomerase VI (topo VI) is a type IIB DNA topoisomerase predominantly found in archaea and some bacteria, as well as plants and algae. It has been discovered that topo VI preferentially decatenates DNA crossings by having a preference for certain DNA crossing geometries. Additionally, topo VI exhibits increased ATPase activity, DNA binding, and rate of strand passage with increasing DNA writhe, providing further evidence that it acts as a DNA crossing sensor. The study suggests that topo VI has evolved an intrinsic preference for the unknotting and decatenation of interlinked chromosomes by sensing and preferentially unlinking DNA crossings with geometries close to 90 degrees.