Direct in vitro selection of titanium-binding epidermal growth factor

Epidermal growth factor (EGF) with affinity to TiO2 surfaces was obtained by direct in vitro selection. A random peptide library was generated for fusion to the N-terminal of EGF, and polypeptides exhibiting affinity were selected in vitro by ribosome display. The best-performing polypeptide sequence was selected for synthesis using a solid-phase method and showed high affinity to TiO2 after refolding. Molecular dynamic simulations indicated that the interaction of the selected peptide segment with the TiO2 surface was comparable to that of a previously reported titanium-binding peptide, TBP-1. The hydroxyl groups in the selected peptide segment were found to be critical for the binding interaction. NIH3T3 cell culture for two days in the presence of the TiO2-binding EGF showed that it was able to enhance cell proliferation as much as unmodified EGF in solution. As a result, the selected EGF construct was able to induce cell proliferation on titanium surfaces. This direct in vitro selection technique should extend the possibilities for the design of other surface-binding growth factors.