Crystallization and preliminary X-ray diffraction studies of the epsilon zeta addiction system encoded by Streptococcus pyogenes plasmid pSM19035

The proteins encoded by the Streptococcus pyogenes broad-host range and low copy-number plasmid pSM19035 form a toxin-antitoxin module that secures st able maintenance by causing the death of plasmid-free segregants. The epsil on zeta protein complex was crystallized in four different forms at pH 5.0 and pH 7.0 using the vapour-diffusion method with PEG 3350 and ethylene gly col as precipitants. Three of the crystal forms were obtained in the same d roplet under identical conditions at pH 5.0. One form belongs to the enanti omorphic space groups P4(3)2(1)2 or P4(1)2(1)2. For the other two, the X-ra y reflection conditions match those of space group P2(1)2(1)2(1), one repre senting a superlattice of the other. A crystal form growing at pH 7.0 also belongs to space group P2(1)2(1)2(1), but there is no indication of a struc tural relationship to the other orthorhombic forms. Initially, the crystals diffracted to 2.9 Angstrom resolution and diffracted to 1.95 Angstrom afte r soaking at pH 7.0. A preparation of selenomethionyl epsilon zeta protein complex yielded single crystals suitable for X-ray diffraction experiments using synchrotron sources.