Biological libraries

Anti-β2-glycoprotein I paratopes and β2-glycoprotein I epitopes characterization using random peptide libraries

Studies concerning interactions between anti-β2-glycoprotein I antibodies (anti-β2GPI) and β2-glycoprotein I (β2GPI) suggest relevance of charge interactions and hydrogen bonds. However, paratope of diagnostically and clinically relevant anti-β2GPI and epitope characteristics of β2GPI, still remain unclear. The aim of our study was to determine paratope characteristics of various anti-β2GPI antibodies and epitope characteristics of β2GPI using phage display. Monoclonal IgG anti-β2GPI, purified polyclonal high avidity and low avidity IgG anti-β2GPI derived from plasma of APS patients were used to screen phage display libraries. The affinity and competition ability of selected clones were evaluated. Various heptapeptides presenting putative paratopes of anti-β2GPI and specific heptapeptides presenting putative epitopes of β2GPI were determined. Epitope presenting peptides bind to the respective anti-β2GPI and consequently interrupt antibody-antigen interaction. The amino acid composition of selected peptides confirmed the importance of hydrogen bonds and charge interactions in the binding of anti-β2GPI to the antigen. Epitopes recognized by high avidity anti-β2GPI predominately contain hydrogen bond forming side chains, while in low avidity anti-β2GPI epitope the charged side chains prevail. The alignment of selected sequences to three-dimensional antigen structure revealed that polyclonal high avidity anti-β2GPI recognize native epitopes that are accessible regardless of β2GPI's conformation whereas the epitope recognized by low avidity anti-β2GPI is cryptic and cannot be accessed when β2GPI takes the closed plasma conformation.

Identification of a ligand for IgG-Fc derived from a soluble peptide library based on fusion proteins secreted byS. cerevisiae

Biological libraries are important tools in the development of new peptide-based compounds. Here, we describe the use of a soluble peptide library system as a complementary tool in the field of ligand development. Random peptides were expressed in S. cerevisiae as carboxy-terminal extensions of the eukaryotic initiation factor 5a (eIF5a) and secreted into the culture supernatant. Expression and screening of this library were performed in a microwell format. As an example of this versatile approach, we describe the identification of a ligand for the human IgG-Fc fragment. Ligands binding IgG-Fc show great potential in a wide variety of applications including development of therapeutics, streamlining the large-scale purification of antibodies, and applications in diagnostic tests. We demonstrated the utility of this system. After screening only 6160 clones, we identified a ligand with the peptide sequence of TRRRTCSPPTWPRARARSTPSGCSSTGPSANRG. An affinity constant of 3.9 x 10(5) M(-1) was determined by a biosensor method. Handling and maintenance of this library is conceptually simple and highly applicable for automated high-throughput systems.