Crystal structure of an anti-carbohydrate antibody directed against Vibrio cholerae O1 in complex with antigen: Molecular basis for serotype specificity

^†Unité de Biochimie Structurale (Centre National de la Recherche Scientifique, Unité de Recherche Associée 2185), ^*Unité du Choléra et des Vibrions, ^‡Unité d'Immunologie Structurale, and ^§Laboratoire d'Ingénierie des Anticorps, Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris, France; and ^¶Laboratory of Medicinal Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0815.

Communicated by John B. Robbins, National Institutes of Health, Bethesda, MD (received for review November 5, 1999)

Abstract

The crystal structure of the murine Fab S-20-4 from a protective anti-cholera Ab specific for the lipopolysaccharide Ag of the Ogawa serotype has been determined in its unliganded form and in complex with synthetic fragments of the Ogawa O-specific polysaccharide (O-SP). The upstream terminal O-SP monosaccharide is shown to be the primary antigenic determinant. Additional perosamine residues protrude outwards from the Ab surface and contribute only marginally to the binding affinity and specificity. A complementary water-excluding hydrophobic interface and five Ab–Ag hydrogen bonds are crucial for carbohydrate recognition. The structure reported here explains the serotype specificity of anti-Ogawa Abs and provides a rational basis toward the development of a synthetic carbohydrate-based anti-cholera vaccine.

Footnotes

↵ ‖ To whom reprint requests should be addressed at: Unité de Biochimie Structurale, Institut Pasteur, 25, rue du Dr. Roux, 75724 Paris Cédex 15, France. E-mail: alzari{at}pasteur.fr.
Data deposition: The atomic coordinates have been deposited in the Protein Data Bank, www.rcsb.org (PDB ID codes 1F4W, 1F4X, and 1F4Y).
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.060022997.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.060022997
Abbreviations:

CDR,

complementarity-determining regions;

LPS,

lipopolysaccharide;

O-SP,

O-specific polysaccharide