title: The three-dimensional structure of a complex of a murine Fab (NC10. 14) with a potent sweetener (NC174): an illustration of structural diversity in antigen recognition by immunoglobulins.
abstract: The three-dimensional structure of a complex of an Fab from a murine IgG2b(lambda) antibody (NC10.14) with a high potency sweet tasting hap- ten, N-(p-cyanophenyl)-N'-(diphenylmethyl)-N"-(carboxymethyl)guan idine (NC174), has been determined to 2.6 A resolution by X-ray crystallography. This complex crystallized in the triclinic space group P1, with two molecules in the asymmetric unit. In contrast to a companion monoclonal antibody (NC6.8) with a kappa-type light chain and similar high affinity for the NC174 ligand, the NC10.14 antibody possessed a large and deep antigen combining site bounded primarily by the third complementarity-determining regions (CDR3s) of the light and heavy chains. CDR3 of the heavy chain dominated the site and its crown protruded into the external solvent as a type 1' beta-turn. NC174 was nested against HCDR3 and was held in place by two tryptophan side-chains (L91 and L96) from LCDR3. The diphenyl rings were accommodated on an upper tier of the binding pocket that is largely hydrophobic. At the floor of the site, a positively charged arginine side-chain (H95) stabilized the orientation of the electronegative cyano group of the hapten. The negative charge on the acetate group was partially neutralized by a hydrogen bond with the phenolic hydroxyl group of tyrosine H58. Comparisons of the modes of binding of NC174 to the NC6.8 and NC10.14 antibodies illustrate the enormous structural and mechanistic diversity manifest by immune responses.
authors.affiliation: Crystallography Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, 73104, USA.
authors.forename: L W
authors.initials: LW
authors.lastname: Guddat
authors.forename: L
authors.initials: L
authors.lastname: Shan
authors.forename: C
authors.initials: C
authors.lastname: Broomell
authors.forename: P A
authors.initials: PA
authors.lastname: Ramsland
authors.forename: Z
authors.initials: Z
authors.lastname: Fan
authors.forename: J M
authors.initials: JM
authors.lastname: Anchin
authors.forename: D S
authors.initials: DS
authors.lastname: Linthicum
authors.forename: A B
authors.initials: AB
authors.lastname: Edmundson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000918:Antibody Specificity / Q000276:immunology; D000936:Antigen-Antibody Complex / Q000737:chemistry* / Q000276:immunology*; D001666:Binding Sites, Antibody; D018360:Crystallography, X-Ray; D006241:Haptens / Q000737:chemistry / Q000276:immunology; D006801:Humans; D006860:Hydrogen Bonding; D007128:Immunoglobulin Fragments / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D007147:Immunoglobulin Light Chains / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D008024:Ligands; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013549:Sweetening Agents / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000936:Antigen-Antibody Complex; D006241:Haptens; D007128:Immunoglobulin Fragments; D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains; D008024:Ligands; D013549:Sweetening Agents