Crystallization of Doc and the Phd:Doc toxin-antitoxin complex

The phd/doc addiction system is responsible for the stable inheritance of lysogenic bacteriophage P1 in its plasmidic form in Escherichia coli and is the archetype of a family of bacterial toxin-antitoxin modules. The His66Tyr mutant of Doc (DocH66Y) was crystallized in space group P21, with unit-cell parameters a = 53.1 A, b = 198.0 A, c = 54.1 A, beta = 93.0°. These crystals diffract to 2.5 A resolution and probably contain four dimers of Doc in the asymmetric unit. DocH66Y in complex with a 22-amino-acid C-terminal peptide of Phd (Phd52-73Se) was crystallized in space group C2, with unit-cell parameters a = 111.1 A, b = 38.6 A, c = 63.3 A, beta = 99.3°, and diffracted to 1.9 A resolution. Crystals of the complete wild-type Phd-Doc complex belong to space group P3121 or P3221, have an elongated unit cell with dimensions a = b = 48.9 A, c = 354.9 A and diffract to 2.4 A resolution using synchrotron radiation.