A de novo designed template for generating conformation-specific antibodies that recognize alpha-helices in proteins

The generation of antibodies directed toward the surface-exposed regions of a protein using synthetic peptides as immunogens representing surface loops and turns has been widely successful. However, peptides representing alpha-helical regions are typically unstructured in solution and unable to produce antibodies that recognize alpha-helices in native proteins. We describe a de novo designed parallel two-stranded alpha-helical coiled-coil template for immunization to prepare antibodies that recognize alpha-helical protein sequences in the native protein. This template was designed for maximum stability through an Ile/Leu hydrophobic core and an interchain disulfide bridge. Surface-exposed helical residues are inserted into the template and used for immunization to generate polyclonal antibodies. To demonstrate the feasibility of this approach, 15 residues of the yeast transcription factor GCN4 were inserted into this template, and the resultant antibodies were screened for conformational specificity. Peptide antigens that contain the same surface-exposed residues but differ in structure were used as competitors in a competition assay. Direct competition between the capture peptide immobilized on a biosensor chip, the peptide antigens, and the antibodies generated by the template demonstrated that the antibodies were specific for helical structure in the native coiled-coil (synthetic GCN4 residues 250-280). These antibodies were unable to recognize the same inserted sequence in an unstructured analog. The helix-specific antibodies were also able to identify native GCN4 (31.3 kDa) from yeast whole cell extracts.