The 24 kDa N-terminal sub-domain of the DNA gyrase B protein binds coumarin drugs

A number of lines of evidence suggest that the N-terminal sub-domain of the DNA gyrase B protein contains the binding site for the coumarin antibiotics. We have engineered a clone which encodes a 24 kDa protein which represents this domain. Bacteria which overproduce this protein show an elevated level of resistance to coumarins, suggestive of binding of the 24 kDa protein to the drugs in vivo. In vitro we find that the 24 kDa protein does not interact with the gyrase A or B proteins or with DNA, and fails to hydrolyse ATP or show significant binding to ATP, ADP or ADPNP. However, we show that the 24 kDa protein binds coumarin drugs as tightly as the intact B protein. A number of experiments suggest that the interaction of the coumarins with the protein is predominantly hydrophobic in nature.