Antigen-binding site of immunoglobulin

The **antigen-binding site of immunoglobulin** (also known as the **paratope**) is the specific region at the tip of each arm of an antibody (immunoglobulin) molecule that binds to an antigen. Each immunoglobulin molecule consists of two identical heavy chains and two identical light chains, and possesses two antigen-binding sites, each formed by the variable (V) domains of one heavy and one light chain. Within these variable domains are three short stretches of highly variable amino acid sequence called **complementarity-determining regions (CDRs)**—three from the heavy chain and three from the light chain—that come together to form the antigen-binding site[2][3][4][7]. The precise structure of these CDRs determines the specificity of the antibody for a particular antigen epitope. These sites are not considered therapeutic targets (e.g., receptors or enzymes) themselves but are functional regions within the broader immunoglobulin (antibody) molecule, which is the actual biological and sometimes therapeutic entity[2][5][6][7].

Other names

ParatopeAntibody binding site