DNA Gyrase from E.Coli is an enzyme belonging to the class of Topoisomerases, which allows the organism to modify the topology of its DNA. In other words it helps untangle, un-knot and relax supercoils in its DNA genome. It does so by binding to a strand of DNA, cutting both strands and then, while keeping hold of both cut ends, passing another piece of double stranded DNA through the gap. It then reseals the double stranded break. Essentially it allows portions of the large circular bacterial genome to pass through itself, such as to prevent knotting and entanglement. A number of antibiotics (e.g. Simocyclinone D8) target this enzyme, since it is essential to the organism's survival. Humans also have a form of this enzyme but it's construction is different and we are thus not affected by the antibiotics.