Hypervariable region

Synonyms

Complementarity-determining region, CDR.

Definition

Hypervariable regions are domains on immunoglobulin heavy and light chains variable regions that are in direct contact with antigen and are frequently mutated to allow diverse antigenic specificities to be recognized.

Full Text

Three areas in the V region of light and heavy chains are highly variable and form distinct loops in the immunoglobulin protein structure. They are termed CDR1, CDR2, and CDR3. The other areas of the V region are more consistent in amino acid sequence and they are referred to as the framework regions (see Figure). The framework regions form β-sheets that provide the structural scaffolding to project these hypervariable region loops. CDRs 1 and 2 are encoded by the V gene segment. In heavy chains, CDR3 is encoded by part of the V_H gene segment, the D_H gene segment, and part of the JH gene segment (Figure). In addition, non-germline encoded nucleotides are added at the junctions of these gene segments....