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 Cd(2+)-to-HP and Cd(2+)-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 of E. coli. Isolated cell envelopes of E. coli bearing newly added metal binding peptides showed an up to 1.8-fold increase in Cd(2+) binding capacity. The bioaccumulation of Cd(2+), Cu(2+), and Zn(2+) by E. coli was evaluated. Surface display of CP multiplied the ability of E. coli to bind Cd(2+) from growth medium fourfold. Display of HP peptide did not contribute to an increase in the accumulation of Cu(2+) and Zn(2+). However, Cu(2+) ceased contribution of HP for Cd(2+) accumulation, probably due to the strong binding of Cu(2+) to HP. Thus, considering the cooperation of cell structures with inserted peptides, the relative 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.