Shiga-like toxins are neutralized by tailored multivalent carbohydrate ligands

The diseases caused by Shiga and cholera toxins account for the loss of millions of lives each year 1 . Both belong to the clinically significant subset of bacterial AB 5 toxins consisting of an enzymatically active A subunit that gains entry to susceptible mammalian cells after oligosaccharide recognition by the B 5 homopentamer 2 , 3 . Therapies might target the obligatory oligosaccharide–toxin recognition event 4 , but the low intrinsic affinity of carbohydrate–protein interactions hampers the development of low-molecular-weight inhibitors 5 . The toxins circumvent low affinity by binding simultaneously to five or more cell-surface carbohydrates 6 . Here we demonstrate the use of the crystal structure of the B 5 subunit of Escherichia coli O157:H7 Shiga-like toxin I (SLT-I) in complex with an analogue of its carbohydrate receptor 6 to design an oligovalent, water-soluble carbohydrate ligand (named STARFISH), with subnanomolar inhibitory activity. The in vitro inhibitory activity is 1–10-million-fold higher than that of univalent ligands and is by far the highest molar activity of any inhibitor yet reported for Shiga-like toxins I and II. Crystallography of the STARFISH/Shiga-like toxin I complex explains this activity. Two trisaccharide receptors at the tips of each of five spacer arms simultaneously engage all five B subunits of two toxin molecules.