A<i>β</i>-Like Peptide Displayed on Bacteriophage T7 Catalyzes Chromate and Uranyl Reduction

Abstract

In order to discover genes capable of catalyzing the reductive immobilization of toxic chromate and uranyl ions, we have created a T7 bacteriophage library containing cDNA from environmental microbes (i.e., Geobacter sulfurreducens and Shewanella oneidensis MR-1) that are known to mediate the reduction of chromate and uranyl ions. After three rounds of screening, ten bacteriophage mutants were found to mediate the NADH-dependent reduction of chromate and uranyl ions whose cDNA encodes polypeptide chains ranging 14 to 73 amino acids in length. All identified sequences contain disordered structural motifs similar to the β-amyloid peptide (Aβ) known to promote aggregation and formation of high-affinity metal binding sites. Confirmation of this structural similarity involved phage display of the 42 amino-acid Aβ-peptides that have been found to catalyze the NADH-dependent reduction of both chromate and uranyl ions. Transmission electron microscopy (TEM) and X-ray absorption near edge structure (XANES) measurements confirm that reduced uranium is present on the surface of bacteriophage expressing the Aβ-peptide. The surface-displayed Aβ-like peptide on bacteriophage has the potential to couple naturally occurring electron transfer shuttles present in soils to promote economically viable remediation of contaminated sites containing toxic chromate and uranyl ions.