Screening of a library of phage-displayed peptides identifies human bcl-2 as a taxol-binding protein

A random library of phage displayed peptides was screened for binding to a biotinylated derivative of paclitaxel (Taxol). Affinity-selected peptides were analyzed for similarity to human proteins. There was no significant similarity between the paclitaxel-selected peptides and tubulin. However, a subset of the peptides was identified that exhibits significant similarity to a non-conserved region of the anti-apoptotic human protein Bcl-2: ELISA assays confirmed binding of paclitaxel to Bcl-2, and circular dichroism spectroscopy demonstrated that a substantial conformational change accompanies this binding. In vivo, treatment with paclitaxel has been shown to lead to Bcl-2 inactivation with concomitant phosphorylation of residues in a disordered, regulatory loop region of the protein. Similarity between paclitaxel-selected peptides and this loop region implicate these residues in drug binding, and suggest that the apoptotic action of paclitaxel may involve the binding of paclitaxel to Bcl-2. These results demonstrate that peptides displayed on the surface of bacteriophage particles can mimic the ligand-binding properties of disordered regions of proteins.