Structure of the Shiga-like Toxin I B-Pentamer Complexed with an Analogue of Its Receptor Gb3

• Published in: Biochemistry (Easton) Vol. 37; no. 7; pp. 1777 - 1788
• Main Authors: Ling, Hong, Boodhoo, Amechand, Hazes, Bart, Cummings, Maxwell D, Armstrong, Glen D, Brunton, James L, Read, Randy J
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17.02.1998
• Subjects: BACTERIAL TOXINS; Bacterial Toxins - chemistry; Bacterial Toxins - metabolism; Bacterial Toxins - toxicity; BINDING SITES; Computer Simulation; Crystallography, X-Ray; Enterotoxins - chemistry; ESCHERICHIA COLI; Escherichia coli - chemistry; Macromolecular Substances; Models, Molecular; Protein Conformation; PROTEIN SUBUNITS; Receptors, Cell Surface - chemistry; Receptors, Cell Surface - metabolism; Receptors, Cell Surface - physiology; Shiga Toxin 1; TOXINAS BACTERIANAS; TOXINE BACTERIENNE; Trihexosylceramides - chemistry; Trihexosylceramides - metabolism; Trihexosylceramides - physiology
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi971806n

Shiga-like toxin I (SLT-I) is a virulence factor of Escherichia coli strains that cause disease in humans. Like other members of the Shiga toxin family, it consists of an enzymatic (A) subunit and five copies of a binding subunit (the B-pentamer). The B-pentamer binds to a specific glycolipid, globotriaosylceramide (Gb3), on the surface of target cells and thereby plays a crucial role in the entry of the toxin. Here we present the crystal structure at 2.8 Å resolution of the SLT-I B-pentamer complexed with an analogue of the Gb3 trisaccharide. The structure reveals a surprising density of binding sites, with three trisaccharide molecules bound to each B-subunit monomer of 69 residues. All 15 trisaccharides bind to one side of the B-pentamer, providing further evidence that this side faces the cell membrane. The structural model is consistent with data from site-directed mutagenesis and binding of carbohydrate analogues, and allows the rational design of therapeutic Gb3 analogues that block the attachment of toxin to cells.