Selection of cadmium specific hexapeptides and their expression as OmpA fusion proteins in Escherichia coli

In searching for novel peptides with affinity for cadmium, the phage display technique was utilized. In the selection procedure, cadmium ions were immobilized on a metal chelating Sepharose gel. The peptides selected from a hexapeptide library showed no homology to naturally occurring metallothioneins. From the phage clones selected in the biopanning process, phages with affinity for Cd-109 in free solution were identified. The peptide His-Ser-Gln-Lys-Val-Phe, which was found to exhibit the strongest relative affinity for Cd-109, was cloned into Escherichia coli as a fusion to the cell surface exposed area of the outer membrane protein OmpA. Escherichia coli cells expressing this peptide showed increased survival in growth media containing up to 1.2 mM CdCl2 when compared with cells not expressing this peptide on their surface.