The endogenous substrate for the ligand binding site in the ATPase domain of human Topoisomerase IIalpha (hTopoIIalpha) is Adenosine triphosphate (ATP). The binding of ATP to the ATP-binding site results into dimerization of two N-terminal domains, thus progressing the catalytic cycle of hTopoIIalpha to next step. In this structure, the two ATP-binding sites located at the surface of ATPase domain are occupied with ATP-molecules. This structure can be used to understand the molecular recognition interactions of ATP with hTopoIIalpha.