A type II topoisomerase. Despite its similarity to DNA gyrase, this enzyme is not able to supercoil DNA, and instead acts like topoisomerase IV. Relaxes both positively and negatively supercoiled DNA in an ATP-dependent fashion, decatenates interlocked circles. If this subunit is reconstituted with GyrA from E.coli the hybrid enzyme supercoils relaxed plasmid DNA; if paired with E.coli ParC supercoiling is not restored. This the first bacteria shown to not contain DNA gyrase, although it has 2 copies of a reverse gyrase that introduces positive supercoils. Type II topoisomerases break and join 2 DNA strands simultaneously in an ATP-dependent manner (PubMed:21076033). 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+). Optimum temperature is 70 degrees Celsius, active between 37 and 90 degrees Celsius. Heterotetramer, composed of two GyrA and two GyrB chains. In the heterotetramer, 'GyrA' contains the active site tyrosine that forms a transient covalent intermediate with DNA, while 'GyrB' binds cofactors and catalyzes ATP hydrolysis (PubMed:21076033). Belongs to the type II topoisomerase GyrB family.