PURIFICATION AND CRYSTALLIZATION OF SHIGA TOXIN FROM SHIGELLA-DYSENTERIAE

The protein toxin produced by Shigella dysenteriae consists of one enzymatically active A subunit of 293 amino acid residues and five B subunits of 69 amino acid residues that are involved with cell attachment. The holotoxin has been purified by blue Sepharose and chromatofocusing column chromatography. Two crystal forms of purified holotoxin have been grown by vapor diffusion. One grows as fine needles, hexagonal in cross section, which do not diffract well enough to characterize crystallographically. The second grows as thin plates that diffract to at least 3 Å resolution. Their space group is P212121 with unit cell dimensions of a = 132.0 Å, b = 146.0 Å and c = 82.5 Å. The asymmetric unit of the crystals is likely to contain two AB5 units.