Towards assignment of secondary structures by anti-peptide antibodies. Specificity of the immune response to a beta-turn.

In an attempt to assign secondary structure elements to protein primary structures with antibodies, we synthesized a model peptide (beta-peptide: TVTVTDPGQTVTY) with a putative beta-turn structure and analysed the anti-peptide antibodies for their specificity towards the turn sequence. At least 50% of the peptide fraction adopts the intended conformation of a beta-turn (DPGQ) inserted between the two segments of an antiparallel beta-sheet structure. The specific anti-beta-peptide antibodies of the hyperimmune response bind the beta-turn containing epitope of the immunogenic beta-peptide with a three orders of magnitude higher affinity than the synthetic control peptide (Gly-peptide: GGGGGDPGQGGGG). The affinity of the antibodies with specificity for the beta-turn region increases from the primary to the hyperimmune response. Therefore, probing of secondary structure elements, i.e., of individual beta-turn regions, by anti-peptide antibodies now seems feasible for proteins of known sequence and may result in sequence assignments of secondary structures.