Type II topoisomerase (topoII) is a metalloenzyme targeted by clinical antibiotics and anticancer agents. Here, we integrate existing structural data with molecular simulation and propose a model for the yet uncharacterized structure of the reactant state of topoII. This model describes a canonical two-metal-ion mechanism and suggests how the metals could rearrange at the catalytic pocket during enzymatic turnover, explaining also experimental evidence for topoII inhibition. These results call for further experimental validation.