Galactose‐binding site in Escherichia coli heat‐labile enterotoxin (LT) and cholera toxin (CT)

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Abstract
Summary: The galactose‐binding site in cholera toxin and the closely related heat‐labile enterotoxin (LT) from Escherichia coli is an attractive target for the rational design of potential anti‐cholera drugs, in this paper we analyse the molecular structure of this binding site as seen in several crystal structures, including that of an LT: galactose complex which we report here at 2.2 Å resolution. The binding surface on the free toxin contains several tightly associated water molecules and a relatively flexible loop consisting of residues 51–60 of the B subunit. During receptor binding this loop becomes tightly ordered by forming hydrogen bonds jointly to the GM1 pentasaccharide and to a set of water molecules which stabilize the toxin: receptor complex.