title: Phage display-selected sequences of the heavy-chain CDR3 loop of the anti-digoxin antibody 26-10 define a high affinity binding site for position 16-substituted analogs of digoxin.
abstract: The heavy-chain CDR3 region of the high affinity (K(a) = 1.3 x 10(10) M(-)1) anti-digoxin monoclonal antibody 26-10 was modified previously to shift its specificity, by substitution of tryptophan 100 by arginine, toward binding analogs of digoxin containing substitutions at position 16. To further change specificity, two 5-mer libraries of the randomly mutagenized phage-displayed 26-10 HCDR3 region (positions 94-98) were panned against digoxin-bovine serum albumin (BSA) as well as against 16-acetylgitoxin-BSA. When a mutant Fab that binds 16-substituted analogs preferentially was used as a parent sequence, clones were obtained with affinities for digoxin increased 2-4-fold, by panning on digoxin-BSA yet retaining the specificity shift. Selection on 16-acetylgitoxin-BSA, however, resulted in nine clones that bound gitoxin (16-OH) up to 150-fold higher than the wild-type 26-10, due to a consensus mutation of Ser(H95) to Gly(H95). The residues at both position H95 (serine) and position H100 (tryptophan) contact hapten in the crystal structure of the Fab 26-10-digoxin complex. Thus, by mutating hapten contact residues, it is possible to reorder the combining site of a high affinity antibody, resulting in altered specificity, yet retain or substantially increase the relative affinity for the cross-reactive ligand.
authors.affiliation: Department of Surgery, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02129, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Krykbaev
authors.forename: W R
authors.initials: WR
authors.lastname: Liu
authors.forename: P D
authors.initials: PD
authors.lastname: Jeffrey
authors.forename: M N
authors.initials: MN
authors.lastname: Margolies
mesh_terms: D000906:Antibodies / Q000737:chemistry*; D000915:Antibody Affinity; D000918:Antibody Specificity; D001665:Binding Sites; D022801:Complementarity Determining Regions / Q000737:chemistry*; D004077:Digoxin / Q000031:analogs & derivatives / Q000276:immunology*; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry*; D016297:Mutagenesis, Site-Directed; D019151:Peptide Library; D012710:Serum Albumin, Bovine / Q000276:immunology; D013329:Structure-Activity Relationship
chemical_list: D000906:Antibodies; D022801:Complementarity Determining Regions; D007143:Immunoglobulin Heavy Chains; D019151:Peptide Library; D012710:Serum Albumin, Bovine; D004077:Digoxin