Novel binding site identified in a hybrid between cholera toxin and heat-labile enterotoxin: 1.9 A crystal structure reveals the details.

• A hybrid between the B subunits of cholera toxin and Escherichia coli heat-labile enterotoxin has been described, which exhibits a novel binding specificity to blood group A and B type 2 determinants. In the present investigation, we have determined the crystal structure of this protein hybrid, termed LCTBK, in complex with the blood group A pentasaccharide GalNAcalpha3(Fucalpha2)Galbeta4(Fucalpha3)GlcNAcbeta, confirming not only the novel binding specificity but also a distinct new oligosaccharide binding site. Binding studies revealed that the new specificity can be ascribed to a single mutation (S4N) introduced into the sequence of Escherichia coli heat-labile enterotoxin. At a resolution of 1.9 A, the new binding site is resolved in excellent detail. Main features include a complex network of water molecules, which is well preserved by the parent toxins, and an unexpectedly modest contribution to binding by the critical residue Asn4, which interacts with the ligand only via a single water molecule.

Keyword

Asparagine

metabolism

Bacterial Toxins

chemistry

genetics

metabolism

Binding Sites

Blood Group Antigens

metabolism

Cholera Toxin

chemistry

genetics

metabolism

Crystallography

X-Ray

Drug Design

Enterotoxins

chemistry

genetics

metabolism

Escherichia coli Proteins

chemistry

genetics

metabolism

Glycosphingolipids

chemistry

metabolism

Humans

Models

Molecular

Molecular Sequence Data

Molecular Structure

Oligosaccharides

chemistry

metabolism

Protein Binding

Protein Structure

Tertiary

Protein Subunits

chemistry

genetics

metabolism

Recombinant Fusion Proteins

chemistry

genetics

metabolism

Water

chemistry

Water

Publication and Content Type

ref (subject category)

art (subject category)