Enhanced bioaccumulation of heavy metal ions by bacterial cells due to surface display of short metal binding peptides

Metal binding peptides of sequences Gly-His-His-Pro-His-Gly (named HP) and Gly-Cys-Gly-Cys-Pro-Cys-Gly-Cys-Gly (named CP) were genetically engineered into LamB protein and expressed in Escherichia coli. The Cd2+ to-HP and Cd2 +-to CP stoichiometries of peptides were 1:1 and 3:1, respectively. Hybrid LamB proteins were found to be properly folded in the outer membrane off, c oli. isolated cell envelopes of E. coli bearing newly added metal binding p eptides showed an up to 1.8-fold increase in Cd2+ binding capacity. The bio accumulation of Cd2+, Cu2+, and Zn2+ by E coli was evaluated. Surface displ ay of CP multiplied the ability of E. coli to bind Cd2+ from growth medium fourfold. Display of RP peptide did not contribute to an increase in the ac cumulation of Cu2+ and Zn2+. However, Cu2+ ceased contribution of HP for Cd 2+ accumulation, probably due to the strong binding of Cu2+ to RP. Thus, co nsidering the cooperation of cell structures with inserted peptides, the re lative affinities of metal binding peptide and, for example, the cell wall to metal ion should be taken into account in the rational design of peptide sequences possessing specificity for a particular metal.