title: Crystal structure of an anticholera toxin peptide complex at 2.3 A.
abstract: Cholera toxin peptide 3 (CTP3) is a 15-residue peptide corresponding in sequence to an immunogenic loop on the surface of the B-subunits of both cholera toxin and the heat-labile toxin from Escherichia coli. TE33 is the Fab fragment of a monoclonal antibody elicited against CTP3. The crystal structure of the TE33-CTP3 complex at 2.3 A resolution reveals an antigen-binding pocket, 13 A deep and 13 A wide, which is lined with many aromatic residues. The N-terminal portion of the peptide antigen CTP3 forms a type II beta-turn that fits snugly into this pocket. At gln7 the peptide backbone of CTP3 forms a kink followed by an extended C-terminal chain that seals off the cleft and buries the beta-turn underneath it. All six complementarity-determining regions of TE33 contribute to the binding of CTP3. The antibody-peptide contacts include, in addition to van der Waals' interactions and hydrogen bonds, also one salt bridge and one water molecule, which mediates the interaction.
authors.affiliation: Case Western Reserve University, School of Medicine, Department of Biochemistry, Cleveland, OH 44106-4935.
authors.forename: M
authors.initials: M
authors.lastname: Shoham
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex / Q000737:chemistry; D001666:Binding Sites, Antibody; D002772:Cholera Toxin / Q000737:chemistry*; D000939:Epitopes / Q000737:chemistry*; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D000939:Epitopes; D007140:Immunoglobulin Fab Fragments; D010446:Peptide Fragments; D014867:Water; C050310:cholera toxin, B subunit (50-64); D002772:Cholera Toxin