Molecular Design of Inorganic-Binding Polypeptides
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John Spencer Evans, Ram Samudrala, Tiffany R. Walsh, Ersin Emre Oren, and Candan Tamerler Abstract Controlled binding and assembly of peptides onto inorganic substrates is at the core of bionanotechnology and biological-materials engineering. Peptides offer several unique advantages for developing future inorganic materials and systems. First, engineered polypeptides can molecularly recognize inorganic surfaces that are distinguishable by shape, crystallography, mineralogy, and chemistry. Second, polypeptides are capable of self-assembly on specific material surfaces leading to addressable molecular architectures. Finally, genetically engineered peptides offer multiple strategies for their functional modification. In this article, we summarize the details and mechanisms involved in combinatorial-polypeptide sequence selection and inorganic-material recognition and affinity, and outline experimental and theoretical approaches and concepts that will help advance this emerging field.
Introduction During the last two decades, combinatorial-peptide selection methods1–3 have been used to generate sequence libraries that recognize and bind to different inorganic solids.4–12 Surface-exposed or displayed polypeptides produced by phage5,7–10,12 and bacteria4,6,10,11 have become the predominant in vivo techniques for material-specific peptide selection, and inorganic-binding peptides are quickly becoming molecular tools for biotechnological and nanotechnological applications. With 20 naturally occurring amino acids available for use, biological organisms can craft an extremely large and diverse set of linear sequences for a wide range of materials, including metals, oxides, semiconductors, and minerals. In addition to the numerous linear combinations, the potential two- and threedimensional configurations of these sequences add another dimension in that there are a number of polypeptide backbone geometries (i.e., secondary structures) that form from different amino-acid sequences of these peptides. Hence, factors such as polypeptide–material affinity and selectivity ultimately are chosen by 514
the sequence and its molecular architecture as well as the chemical composition of the peptide.13,14 Thus, a successful design of polypeptide-inorganic materials is dependent upon our understanding of the molecular factors that govern sequence–structure–function selection. This article will summarize our current knowledge of phage and bacterialgenerated polypeptides directed against inorganic solids, using examples obtained from experiment and theory to define the molecular trends emerging from the screened polypeptide libraries generated against artificial and biological inorganic materials such as Pt, Au, hydroxyapatite, graphite, and quartz.
First-Generation Peptides and Post-Selection Engineering A genetically engineered polypeptide for inorganics (GEPI) is defined as an aminoacid sequence that specifically and selectively binds to an inorganic surface.10 Bacterial-cell surface (BCS) and phage display (PD) libraries have been ad
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