Part:BBa_K3512001

ccdB Toxin

The CcdB toxin is part of the CcdA-CcdB system. The target of CcdB is the GyrA subunit of DNA gyrase, an essential type II topoisomerase in Escherichia coli. Gyrase alters DNA topology by effecting a transient double-strand break in the DNA backbone, passing the double helix through the gate and resealing the gaps. The CcdB toxin acts by trapping DNA gyrase in a cleaved complex with the gyrase A subunit covalently closed to the cleaved DNA, causing DNA breakage and cell death in a way closely related to quinolones antibiotics.

In absence of the antitoxin CcdA, the CcdB toxin traps DNA-gyrase cleavable complexes, inducing breaks into DNA and cell death.