Zinc ion (Zn 2+ ) can be coordinated with four or three amino acid residues to stabilize a protein's structure or to form a catalytic active center. We used phage display selection of a dodecamer random peptide library with Zn 2+ to identify structural zinc sites. The binding speci¢city for Zn 2+ of selected sequences was con¢rmed using enzyme-linked immunosorbent and competitive inhibition assays. Circular dichroism spectra indicated that the interaction with Zn 2+ induced a change in conformation, which means the peptide acts as a structural zinc site. Furthermore, a search of protein databases revealed that two selected sequences corresponded to parts of natural zinc sites of copper/zinc superoxide dismutase and zinccontaining ferredoxin. We demonstrated that Zn 2+ -binding sequences selected from the random combinatorial library would be candidates for arti¢cial structural zinc sites. ß