Stabilization of antibody structure upon association to a human carbonic anhydrase epitope studied by X-ray crystallography, microcalorimetry, and molecular dynamics simulations
Abstract
Specific antibodies interfere with the function of human tumor-associated carbonic anhydrase IX (CA IX) and show potential as tools for anticancer interventions. Correlation between structural elements and thermodynamic parameters of the association of antibody fragment Fab M75 to a peptide corresponding to its epitope in the proteoglycan-like domain of CA IX is presented.
Comparisons of the crystal structures of free Fab M75 and its complex with the epitope peptide reveal major readjustments of CDR-H1 and CDR-H3. In contrast, the overall conformations and positions of CDR-H2 and CDR-L2 remain unaltered, and their positively charged residues may thus present a fixed frame for epitope recognition.
Adoption of the altered CDR-H3 conformation in the structure of the complex is accompanied by an apparent local stabilization. Used methods include: translation-libration-screw analysis, isothermal titration microcalorimetry, X-ray analysis, and molecular dynamics simulations.