What is an Epitope?
An epitope refers to the specific target against which an individual antibody binds.

When an antibody binds to a protein, it isn’t binding to the entire full-length protein. Instead, it is binding to a to a segment of that protein known as an epitope. In general, an epitope is approximately five or six amino acids in length. So, a typical full-length protein sequence actually contains many different epitopes against which antibodies can bind.

And, for any given protein sequence, one will typically find that multiple unique antibodies will recognize the protein. Each of these antibodies binds to a specific epitope located on that protein.

Binding between the antibody and the epitope occurs at the Antigen Binding Site, which is called a paratope and is located at the tip of the variable region on the antibody. This paratope is only capable of binding with one unique epitope.

Within a protein sequence, one can find:

  1. Continuous epitopes, which are linear sequences of amino acids
  2. Discontinuous epitopes, which exist only when the protein is folded into a particular conformation.

In the context of developing a custom antibody, it is important to differentiate between targeting a specific epitope on a protein and in simply having antibodies (which may be against a number of epitopes) that recognize a particular protein.

Next: How are Antibodies Produced?