Complementarity-determining regions (CDRs) are polypeptide segments of the variable chains in immunoglobulins (antibodies) and T cell receptors, generated by B-cells and T-cells respectively. CDRs are where these molecules bind to their specific antigen and their structure/sequence determines the binding activity of the respective antibody.

Use the 'Get all CDRs' tab to get a list of all CDRs from all antibody structures. Choose from five different definitions: Chothia, contact, IMGT, Kabat, and North. Search for a subset of CDRs by attribute - such as species, experimental method, resolution, length, sequence etc.

Having obtained the full-length sequence of an antibody, it is important to identify which portions of the sequence correspond to the CDR loops and which to the framework regions.

Genetic recombination of the V, D, and J gene segments for VH and V and J gene segments for VL with subsequent somatic hypermutation in mature B cells accounts for antibody CDR sequence diversity.

The following set of rules will allow you to find the (Kabat or Chothia) CDRs in an antibody sequence. Note that the word 'always' should always be treated with care! There are rare examples where these virtually constant features do not occur (for example the human heavy chain sequence EU does not have Trp-Gly after CDR-H3).