Antigenic peptides.

Although most short, linear peptide fragments of proteins are unstructured in aqueous solution, a number of immunogenic and antigenic peptides have been shown to have conformational preferences for structured forms. By using mainly NMR and CD spectroscopy, it has been possible to detect and quantify quite small populations of beta-turn, helical, and nascent helical conformations. Recent studies have been published indicating that the presence of structured forms is correlated with the location of T cell and/or B cell epitopes in peptide sequences. X-ray crystal structures of complexes between peptides and anti-peptide antibodies frequently show the peptides bound in beta-turn conformations, and the presence of helix in one peptide-antibody complex has been shown by NMR spectroscopy. Studies of peptides free in solution and bound to anti-peptide antibodies in the crystal indicate that the structure of the principal neutralizing determinant of HIV-1 probably includes at least one beta-turn in a highly conserved region. These results can potentially be used in the design of peptide-based vaccines.