title: Crystal structure of the holotoxin from Shigella dysenteriae at 2.5 A resolution.
abstract: Shigella dysenteriae is the pathogen responsible for the severe form of dysentery in humans. It produces Shiga toxin, the prototype of a family of closely related bacterial protein toxins. We have determined the structure of the holotoxin, an AB5 hexamer, by X-ray crystallography. The five B subunits form a pentameric ring, encircling a helix at the carboxy terminus of the A subunit. The A subunit interacts with the B pentamer via this C-terminal helix and a four-stranded mixed beta-sheet. The fold of the rest of the A subunit is similar to that of the A chain of the plant toxin ricin; both are N-glycosidases. However, the active site in the bacterial holotoxin is blocked by a segment of polypeptide chain. These residues of the A subunit would be released as part of the activation mechanism of the toxin.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Canada.
authors.forename: M E
authors.initials: ME
authors.lastname: Fraser
authors.forename: M M
authors.initials: MM
authors.lastname: Chernaia
authors.forename: Y V
authors.initials: YV
authors.lastname: Kozlov
authors.forename: M N
authors.initials: MN
authors.lastname: James
mesh_terms: D000595:Amino Acid Sequence; D001427:Bacterial Toxins / Q000737:chemistry* / Q000235:genetics; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004768:Enterotoxins / Q000737:chemistry; D029968:Escherichia coli Proteins; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D022603:Shiga Toxins; D012762:Shigella dysenteriae / Q000737:chemistry* / Q000235:genetics
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D022603:Shiga Toxins; C027538:heat-labile enterotoxin, E coli