IgG Fab

Immunoglobulin G (IgG) is the most abundant type of antibody found in blood and extracellular fluid and protects body from various bacterial and viral infections by binding those pathogens. IgG antibody is a 150 kDa tetrameric quaternary structure which contains two identical class γ heavy chains of about 50 kDa and two identical light chains of about 25 kDa. The two heavy chains are linked to each other and to a light chain each by disulfide bonds, resulting in a Y-like shape. The antigen-binding (Fab) fragment is a region on an antibody that binds to antigens. It is composed of one constant and one variable domain of each of the heavy and the light chain. The variable domain contains the paratope (the antigen-binding site), comprising a set of complementarity determining regions, at the amino terminal end of the monomer. Each arm of the Y thus binds an epitope on the antigen.