Epitope Mapping: Identiflcation of Antibody- Binding Sites on Protein Antigens

An epitope can be simply defined as that part of an antigen involved in its recogmtion by an antibody In the case of protein antigens, an epitope would consist of a group of mdlvidual ammo-acid side-chains close together on the protein surface Epitope mapping, then, becomes the process of locating the epitope, or identifying the mdividual ammo-acids mvolved Apart from its mtrmsic value for understanding protein structure-function relationships, it also has a practical value in generating antibody probes of defined specificity as research tools and in helping to define the immune response to pathogenic proteins and organisms Some authors have even extended the epitope concept to the mteraction between peptide hormones and then receptors (1) , not every immunologist would be happy about this, but it does make the point that in mapping epitopes, we are studying a biological process of fundamental importance, that of protein-protein mteraction Epitope mapping is usually done with monoclonal antibodies (MAbs), though it can be done with polyclonal antisera in a rather less rigorous way, bearing in mind that antisera behave as mixtures of MAbs. Mapping can be done directly by X-ray crystallography of antibody-antigen complexes, but it can also be done by changing individual ammo-acids, by using antigen fragments and synthetic peptides or by competition methods in which two or more antibodies compete for the same, or adjacent, epitopes. The term “epitope mapping” has also been used to describe the attempt to determine all the major sites on a protein surface that can elicit an antibody response, at the end of which one might claim to have produced an “epitope map” of the protein mununogen (2) This mformatron might be very useful, for example, to someone wishing to produce antiviral vaccines. However, there is a limit to how far one can go down this road, because the map obtained may be influenced by how MAbs are selected and by the mapping method used Furthermore, the more strictly correct definmon of epltope mapping is based on antigenicity (the ability to recognize a specific antibody).