Probing the interface between biomolecules and inorganic materials using yeast surface display and genetic engineering.

Although promising for biomimetic materials applications, polypeptides binding inorganic material surfaces and the mechanism of their function have been difficult to characterize. This paper reports sequence-activity relationships of peptides interfacing with semiconductor CdS, and presents methodologies broadly applicable to studying peptide-solid surface interactions. We first employed yeast surface display with a human repertoire antibody library and identified rarely-occurring scFv fragments as CdS-binding polypeptides. Using our semi-quantitative cell-surface binding assay, site-directed mutational analysis, and genetic engineering we defined short distal regions of the displayed polypeptides necessary and sufficient for CdS binding. Alanine scanning mutagenesis in combination with a series of engineered polyhistidine peptides elucidated a direct relationship between histidine number and binding strength, which appeared to be further modulated by arginine and basic residues. The minimum strength of interaction was established by competition studies using soluble synthetic peptide analogs, which showed half-maximal inhibition of yeast binding to CdS at approximately 2 microM peptide. We then showed the ability of cells displaying material-specific polypeptides to form self-healing biofilms and discriminate between materials of fabricated heterostructure surfaces. Furthermore, we demonstrated the synthetic potential of the selected soluble CdS peptide in mediating aqueous synthesis of fluorescent CdS nanoparticles at room temperature. This platform may be further applied to elucidate mechanisms governing interfacial interactions and to generate material-specific reagents useful in medicine, biosensors, and bioproduction of high value inorganic materials.