Epitope

An epitope (Greek ἐπί epi " at, on " and τόπος topos "place", synonym: antigenic determinant ) is a region of the surface of an antigen to which an antibody or T cell receptor binds specifically. Antibodies are usually directed against proteins and proteids. In rare cases, antibodies against different chemical structures (eg, DNA, saccharides, heavy metals, steroid hormones, penicillin ) can be formed. The opposite face of the epitope on the bound antibody or T- cell receptor is termed the paratope.

A single antigen, such as a membrane protein or a cell of a bacterium carrying different spatial epitopes. Against each of these epitopes can be a specific antibody or a specific T cell can be formed. Epitopes may be art- or individual- specific.

After the phagocytosis of the antigen by antigen presenting cells, these epitopes present on its cell surface. Subsequently, the adaptive immune response.

Properties

Typically possess epitopes that are bound to MHC class I molecules, have a length of 8-11 amino acids, while having MHC class II epitopes, longer peptide chain of about 15 amino acids.

A distinction is made between continuous (synonym Sequenzepitope ) and discontinuous epitopes (synonym conformation ). Proteins consist of chains of amino acids are folded in three dimensions. So epitopes from different nearby in space are amino acid residues can be made, which actually are far apart in the amino acid sequence. Such epitopes are discontinuous called because they are only present in the native state of the protein and can be identified. On SDS - gel electrophoresis followed by Western blotting for example, the amino acid chains are unfolded ( denatured ), and the antibodies no longer bind to a discontinuous epitope, when the epitope is not able to fold into the correct native form again. Contrast, continuous epitopes remain even after denaturation exist, since they consist of a sequence of consecutive amino acids, which is retained during denaturation.

The binding specificity of an antibody to its epitope is referred to as affinity, the sum of the energies of all the binding to an antigen ( multiple epitope ) binding antibodies is referred to as avidity.

Application

In genetic engineering epitopes find application tags (e.g. His-tag, Myc - tag, Strep-tag, V5 -tag, or flash -tag) to allow the fusion protein to the detection of proteins for which no suitable antibody is available stands. For this purpose, the gene of an epitope is incorporated in the same reading frame as the protein to be examined, so that the expressed protein is replaced by an N- or C-terminal epitope tag. Against the attached epitope, an antibody can now be used for detection. The same epitope in different experiments can always be appended to new proteins, and thus also always the same antibodies are used, which represents a considerable effort and cost savings.

The Immune Epitope Database is an online database for previously described epitopes, besides also programs to predict the binding affinity of epitopes to MHC molecules are available (reverse immunology ). The systematic study of the epitopes in an antigen is referred to as epitope mapping.