Topoisomerase IIα C-terminal Domain Mutations and Catalytic Function

Topoisomerase IIα is a nuclear enzyme needed for dealing with topological entanglements in the DNA arising from replication and transcription. The N-terminal region and core of the protein are utilized in the catalytic cycle of the enzyme, which generates a transient double-stranded break in one segment of DNA and passes another segment through the break. The C-terminal domain is a large, intrinsically disordered region that appears to be involved in regulating the function of the enzyme both in terms of substrate selection and the level of activity of the enzyme. In a previous study, we explored eleven targeted mutations to the C-terminal domain. This present study explores six of these mutants to determine whether there are any defects in closure of the N-terminal clamp and whether an experimental compound known as a Cu(II)-thiosemicarbazone affects DNA cleavage with the mutants. Based upon our results, the mutants are able to close the N-terminal clamp, but some of the mutants that displayed the least clamp closing activity also had the lowest catalytic activity. Further, Cu-APY-ETSC did impact the ability of the enzymes to cleave DNA to similar levels as seen with the WT enzyme. These results lay the groundwork for additional analyses of the C-terminal domain and indicate the C-terminal domain regions tested did not influence the action of Cu-APY-ETSC except at the level of coordination between the two active sites.