Engineered biomolecular interactions with inorganic materials : sequence, binding, and assembly

Abstract

Nanobiotechnology aims to exploit biomolecular recognition and self-assembly capabilities for integrating advanced materials into medicine and electronics. In particular, peptides have exhibited the ability to specifically bind to and/or control the synthesis of diverse inorganic and metallic materials including those with electronic, magnetic, and optical properties. However, in order to mature into an engineering discipline, a fundamental understanding of how peptide chemical composition and amino acid spatial arrangement relate to interfacial function and specificity is essential. This work discloses general principles governing peptide-inorganic material surface interactions at the level of amino acid functional groups. To facilitate fundamental studies, methodologies broadly applicable to probing sequence-activity relationships of peptide-inorganic material surface interactions were developed. A yeast surface display system adapted to liquid-solid interfaces enabled surgical manipulation of sequence through genetic techniques and rapid, semi- quantitation of peptide-materials binding strength. Cells displaying material specific polypeptides were also shown to form self-healing biofilms and discriminate between surfaces of fabricated heterostructure materials. The influence of peptide sequence on aqueous formation of photoluminescent CdS nanoparticles was studied with synthetic soluble peptides and higher throughput methods. Systematic study of peptide sequence-activity relationships concluded that surface binding depends primarily on composition; For the single crystalline II-VI semiconductors CdS, CdSe, ZnS, and ZnSe, and polycrystalline Au studied, only residues from the group of histidine, tryptophan, methionine, and cysteine appeared sufficient for significant binding.

(cont.) Additionally, each material exhibited a unique fingerprint of binder- modulator relationships, where spatially proximal amino acids tuned the binding strength of binder-residues in unconstrained peptides. This hierarchal set of compositional and spatial criteria was applied to rationalize sequence-activity relationships observed for genetically identified peptides. Also, peptide binding strength was found to have a curved-linear correlation with the ability to mediate nanoparticle formation; Intermediate peptide-CdS binding strength yielded optimal CdS nanoparticle photoluminescence as did peptides with greater compositional diversity. Finally, by employing the criteria developed herein, we demonstrated the ability to predictively engineer peptides with specific, differential affinities for surfaces of closely related inorganic materials.