Identification and characterization of Cu(2)O- and ZnO-binding polypeptides by Escherichia coli cell surface display: toward an understanding of metal oxide binding.

We have used the FliTrx cell surface display system to identify disulfide-constrained dodecapeptides binding to the semiconducting metal oxides Cu(2)O and ZnO. Sequence analysis of the inserts revealed that the two populations exhibit similar, yet subtly different patterns of amino acid usage. Both sets of binders were enriched in arginine, tryptophan, and glycine with a higher degree of positional preference in the case of Cu(2)O binders. Tyrosine, proline, and serine were underrepresented in both populations. Peptides binding electrodeposited Cu(2)O or ZnO with high avidity could be subdivided into two classes based on pI and hydrophilicity. In the hydrophilic and positively charged Class I binders, the Arg-X-X-Arg tetrapeptide appears to be implicated in metal oxide binding, whereas Arg-Arg and Arg-Lys pairs allow for discrimination between Cu(2)O and ZnO. Molecular dynamics simulations of the disulfide-constrained peptides suggest that the aforementioned motifs are important to properly orient two basic residues that are likely to contact the metal oxides. The implications of our results in understanding the rules governing the interaction between peptides and inorganic compounds and in their use for the design of hybrid nanoarchitectures are discussed.