X-ray crystallography provides a powerful tool for the study of antigen- antibody interactions. Information provided by crystallographic studies of antigen-antibody complexes includes the topological description of intermolecular contacts and the nature of interactions between amino acid residues. In cases where structures of both liganded and unliganded forms of an antigen or antibody fragment are known, crystallographic studies have led to a more dynamic view of binding, often showing conformational changes (induced fit) in the antibody or antigen and displacement of water molecules at the binding interface.
