Shiga-like toxins are neutralized by tailored multivalent carbohydrate ligands

The diseases caused by Shiga and cholera toxins account for the loss of mil lions of lives each year(1). Both belong to the clinically significant subs et of bacterial AB(5) toxins consisting of an enzymatically active A subuni t that gains entry to susceptible mammalian cells after oligosaccharide rec ognition by the B-5 homopentamer(2,3), Therapies might target the obligator y oligosaccharide-toxin recognition event(4), but the low intrinsic affinit y of carbohydrate-protein interactions hampers the development of low-molec ular-weight inhibitors(5). The toxins circumvent low affinity by binding si multaneously to five or more cell-surface carbohydrates(6), Here we demonst rate the use of the crystal structure of the B-5 subunit Of Escherichia col i O157:H7 Shiga-like toxin I (SLT-I) in complex with an analogue of its car bohydrate receptor(6) to design an oligovalent, water-soluble carbohydrate ligand (named STARFISH), with subnanomolar inhibitory activity. The in vitr o inhibitory activity is 1-10-million-fold higher than that of univalent li gands and is by far the highest molar activity of any inhibitor yet reporte d for Shiga-like toxins I and II. Crystallography of the STARFISH/Shiga-lik e toxin I complex explains this activity. Two trisaccharide receptors at th e tips of each of five spacer arms simultaneously engage all five B subunit s of two toxin molecules.