CONSTRAINING B-TURN STRUCTURE IN MODEL IMMUNOGENS

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Immunolglobulin molecules have become valuable reagents in research and diagnostic laboratories and have been tested as clinical reagents in the treatment of disease. Monoclonal antibodies directed to a linear epitope in a globular protein molecule can sometimes be generated by immunizing with linear peptide sequences derived from the native protein. When these antibodies are identified they are generally of low titer and thus not of great utility in the research laboratory or clinic. This is particularly true when this approach has been applied to molecules of the immunoglobulin superfamily. The limited success in generating antipeptide antibodies with a high affinity for the folded protein from which the sequence was derived may arise because the linear peptide conformation does not resemble the structure found in the folded protein. Two methods are proposed to constrain the conformation of linear epitopes in model immunogens. Sequences which occur on the surface of a parent protein in a Beta-turn conformation will be introduced into a cyclic peptide structure which should promote a Beta-turn conformation. These sequences will also be substitited for a Beta-turn region of staphylococcal nuclease at the gene level to produce a hybrid protein immunogen. The affinity of polyclonal and monoclonal antibodies, elicited by the model immunogens, for the parent protein will be compared with antibodies raised against similar linear peptides. The conformation of the cyclic peptides and hybrid proteins will be characterized by NMR spectroscopy and x-ray crystallagrophy to allow a detailed molecular interpretation of the immunological data.