Determination of Epitopes by Mass Spectrometry

As a response to an infection, the immune system produces antibodies. The determination of the antigenic structure recognized by the antibody through epitope mapping provides information about the interaction between antigen and antibody for the diagnosis of a disease on a molecular level, for characterizing the pathogenesis of the infectious material, and for the development of interfering drugs or preventative vaccines. Here we present the determination of the fine structure of the linear epitope located on the gp41 protein of the human immunodeficiency virus recognized by the monoclonal antibody 2F5. In this approach we coupled the antigen SOSgp140 to the antibody 2F5, which was covalently linked to an Fc-specific antibody immobilized on cyanogen bromide (CNBr)-activated Sepharose beads. Digestion of the antigen with endoproteinase LysC resulted in an affinity-bound peptide whose fine structure was characterized by digestion with carboxypeptidase Y and aminopeptidase M. All steps of this method were monitored by matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS). The epitope recognized by 2F5 was identified to be the 16-mer peptide with the sequence NEQELLELDKWASLWN.