Crystallization of CcdB in complex with a GyrA fragment
Plasmid addiction systems consist of a plasmid-encoded toxin–antidote pair that serves to stabilize low-copy-number plasmids in bacterial populations. CcdB, the toxin from the ccd system on the Escherichia coli F plasmid, acts as a gyrase poison. A 14 kDa fragment of gyrase, GyrA14, was found to bind to the toxin CcdB with an affinity of 1.75 × 10−8 M. Crystals of the (GyrA14)2 dimer in its free state belong to space group P43212, with unit-cell parameters a = 86.4, c = 89.4 Å, and diffract to 2.4 Å. Crystals of the (GyrA14)2–(CcdB)2 complex belong to space group P212121, with a = 52.1, b = 83.3, c = 110.9 Å, and diffract to 2.8 Å resolution.
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