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 1.75x10(-8) M. Crystals of the (GyrA14)(2) dimer in its free state belong to space group P4(3)2(1)2, with unit-cell parameters a=86.4, c=89.4 Angstrom, and diffract to 2.4 Angstrom. Crystals of the (GyrA14)(2)-(CcdB)(2) complex belong to space group P2(1)2(1)2(1), with a=52.1, b=83.3, c=110.9 Angstrom, and diffract to 2.8 Angstrom resolution.