Significant structural and functional change of an antigen-binding site by a distant amino acid substitution: proposal of a structural mechanism.
To study the molecular basis for antibody diversity and the structural basis for antigen binding, we have characterized the loss of phosphocholine (P-Cho) binding both experimentally and computationally in U10, a somatic mutant of the antibody S107. Nucleotide sequencing of U10 shows a single base change in JH1, substituting Asp-101 with Ala, over 9 A distant from the P-Cho-binding pocket. Probing with antiidiotypic antibodies suggests local, not global, conformational changes. Computational results support a specific structural mechanism for the loss of P-Cho binding. The U10 mutation eliminates the charged interaction between Asp-101 and Arg-94, which allows the Arg-94 side chain to disrupt P-Cho binding sterically and electrostatically by folding into the P-Cho-binding site. These results specifically show the importance of the Arg-94 to Asp-101 side chain salt bridge in the heavy-chain CDR3 conformation and suggest that residues distant from the binding site play an important role in antibody diversity and inducible complementarity.
Chien
N C
NC
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461.
Roberts
V A
VA
Giusti
A M
AM
Scharff
M D
MD
Getzoff
E D
ED
D000818:Animals; D000906:Antibodies / Q000235:genetics*; D000916:Antibody Diversity; D000936:Antigen-Antibody Complex; D000941:Antigens; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D003198:Computer Simulation; D004797:Enzyme-Linked Immunosorbent Assay; D015321:Gene Rearrangement; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010767:Phosphorylcholine / Q000276:immunology; D011487:Protein Conformation; D013329:Structure-Activity Relationship
D000906:Antibodies; D000936:Antigen-Antibody Complex; D000941:Antigens; D010767:Phosphorylcholine