Puzzling Peptides from a Phage Display Library

The commercial availability of random peptide libraries displayed on the M13 phage is increasing their use forstudies on epitope identification, enzyme inhibitors, receptor ligands, etc. In this study two experimentswhere planned for selection of peptides. First with sheep antibodies, the positive selector was IgG, preparedon Protein G column from a pool of 11 sheeps immunized, with a vaccine prepared from larvae ofLucilia cuprina, against blowfly strike. The negative selector was IgG from the same sheeps before vaccinationand IgG from vaccinated non-immunized sheeps. Four rounds of positive and negative selectionswith IgG from sheep were done respectively. In the second experiment using human IgG prepared ona fresh Protein G column, again four rounds of positive selection with either IgG from MS and schizophreniapatients were performed. This assay was alternated with two negative selections of schizophrenia IgG onMS-associated peptides and vice versa and two negative selections on each with a control IgG. After thefourth negative selection in each experiment, the phage was amplified and random clones were pickedfor nucleotide sequencing. A total of 44 peptides were sorted with the PILEUP program and there was a largenumber of 12-mer peptides containing either 4 or 5 methionine residues.