Synthetic Immunogens for Secondary Structure Assignment: Conformational Sequencing of Proteins with Antipeptide Antibodies

Abstract

Antibodies to proteins can be induced by immunizations with short synthetic peptide immunogens. They have been used for the identification of protein products from open reading frames of nucleic acid sequences of cloned protein genes, structure-function studies, localization of proteins at their functional compartment, topological studies of membrane proteins, virus neutralization, and for experiments on the specificity of the immune system (reviewed in [1, 2]). The high frequency with which protein-reactive antipeptide antibodies can be generated allows the isolation of antibodies of predetermined specificity to most regions of proteins. Not only regions comprising surface-exposed residues, but also sequence stretches from the interior react with their cognate antipeptide antibodies [3,4]. Therefore, the resulting sum of the immunogenicity of the pieces of a protein represented by the synthetic peptide immunogens by far exceeds the immunogenicity of an intact protein, whereby immunogenicity refers to the ability of an antigen, here either a peptide or an intact protein, to induce antibodies. Recognition by an antibody is referred to as antigenicity. Since only a limited part of an intact protein is immunogenic and since antigenic determinants of proteins are often [5] but not always [6] composed of amino-acid residues far apart from each other in the sequence, these determinants are called discontinuous, conformational, and more recently, assembled topographic determinants [5].