Genetically Encoded Coat Protein-Based Yeast Display Libraries of Cyclic Peptides.

Peptide libraries present have improved means to effectively identify epitopes of antibodies, either as monoclonal reagents or polyclonal constituents of the immune response, which includes characterization of vaccination responses, profiling of allergic reactions, and screening of patient samples for autoantibodies. In all of these examples, there is an urgent demand for simple and inexpensive target epitope screening. Here, we present a method for epitope identification, based on the yeast display of overlapping peptides conformationally constrained within the capsid protein PP7 with the aid of a disulfide bridge. Using rituximab as a model antibody, the PP7 scaffold was screened for favorable positions for the grafting of peptides, which should allow high accessibility and efficient cyclization. Libraries of overlapping peptide fragments were then constructed, affinity-selected, and screened to retrieve the correct epitopes of model monoclonal antibodies through the enrichment of affinity-captured sequences. Further, plasma rich in antiglutamic acid decarboxylase (GAD) 65 antibodies, a phenomenon associated with a number of neurological disorders, such as "stiff-person-syndrome", was successfully used as a bait to discover the relevant epitope from the antigen peptide library. The presented system sets the basis for a platform that could contribute to novel diagnostic approaches and the discovery of antigen-specific treatments, conducive to a precision medicine approach superior to generalized immunosuppression.