The ATPase domain of human Topoisomerase IIalpha (hTopoIIalpha) is a homodimeric structure formed by two N-terminal domains. This domain contains two binding sites for the endogenous ligand ATP. Additionally, the dimeric form also contains the ligand binding site for the anticancer agent ICRF-187 and other compounds of this class. This structure represents the apo form of ATPase domain. In this structure, the ATP-binding sites and the ICRF-binding site of ATPase domain are unoccupied with any small molecular ligand so as to understand the intersubunit communications in the absence of any bound ligand.