A type II topoisomerase that negatively supercoils closed circular double-stranded DNA in an ATP-dependent manner. ATP-dependent breakage, passage and rejoining of double-stranded DNA. Binds two Mg(2+) per subunit. The magnesium ions form salt bridges with both the protein and the DNA. Can also accept other divalent metal cations, such as Mn(2+) or Ca(2+). Made up of two chains. The A chain is responsible for DNA breakage and rejoining; the B chain catalyzes ATP hydrolysis. May be due to an intron retention. Belongs to the type II topoisomerase GyrB family.