Antibodies are a powerful weapon system in defending our body against invaders such as bacteria and viruses. Each antibody consists of four amino acidpolypeptide chains: two heavy chains and two light chains joined to form a Y-shaped molecule. Antibodies recognize a specific antigen unique to its target as they possess the antigen-binding sites located at the upper tips of the Y. While antibody-based therapeutics have been established as front-line drugs, little headway has been made in the use of antibodies as research tools in small molecule drug discovery, particularly in the field of x-ray crystallography.