Mutagenesis of Intrinsically Disordered Domain Impacts Topoisomerase II⍺ Catalytic Activity

Human topoisomerase II⍺ and IIb regulate DNA topology and knots in chromosomes during crucial cellular processes making these enzymes common targets for anticancer drugs. However, selective inhibition of topoisomerase II⍺ (TOP2A) is desired to decrease adverse effects, which may be mediated by topoisomerase IIb (TOP2B). The main region of difference between the two isoforms is the intrinsically disordered C-terminal domain (CTD), which is being studied as a target for selective inhibition. Our previous work examined several regions within the CTD to determine whether those regions impact biochemical function. In this current study, we designed and constructed four TOP2A mutants with amino acid substitutions in the CTD, which were then assessed for impact on biochemical activity. V1482D exhibited increased levels of relaxation, while both V1482D and K1520I exhibited increased levels of decatenation. No major impact on DNA cleavage or binding were observed with any of the mutants. The isolated impact of the changes on relaxation and decatenation supports the concept that the CTD can affect one aspect of the enzyme’s function in an isolated manner, which was seen in our previous study. Taken together, these results suggest modification of specific positions within the CTD affects substrate selection. These results are mapped onto the CTD for consideration of potential regions to target for inhibition of TOP2A.