Puzzling peptides from a phage display library

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