A synthetic biology approach for nanomaterial design, synthesis and functionalization

Abstract

Biological formation of inorganic material occurs in most organisms in nature. Various biomolecules such as polypeptides, lipids and metabolites are responsible for biomineralization in cells and tissues. Biological synthesis of biohybrid materials is a recently emerged discipline that uses these biomolecules in synthetic biological systems. Synthetic biology is one of most promising approaches for the development of biohybrid systems, and stands at the intersection of computer science, engineering and molecular genetics. Synthetic biology tools allow the design of programmable genetic toolkits that can compete with natural biosynthesis systems. The present thesis elaborates on the formation of well-controlled genetic systems that can synthesize and functionalize biological materials. Artificial peptides were fused to various genes through molecular genetics techniques, allowing the production of designer proteins. One aspect concerns the fusion of the 19 amino acid-long R5 motif of silaffin protein to three distinct fluorescent proteins. The R5 peptide motif can nucleate silica precursor ions to synthesize silica nanostructures. Therefore, fusion of fluorescent proteins with the R5 motif allows the synthesis and encapsulation of fluorescent silica nanoparticles. Due to its affinity to silica, R5 tag was also shown to be a candidate tag for silica resin-based affinity chromatography purification. Using synthetic biology tools, production of autonomously formed biotemplating platforms can be achieved. A bacterial functional amyloid fiber biosystem called curli can be utilized as a biotemplating platform for nanomaterials synthesis in this context. The major curli subunit CsgA was fused to artificial peptides that can nucleate and synthesize various nanomaterials. Inducible systems were also integrated into the genetic design system to confer temporal control over curli synthesis. These designs were improved through the incorporation of material-sensitive transcription factors and their cognate promoters for ions of cadmium, gold and iron. First, these material sensitive pairs were used in the development of microbial whole cell sensors that produce a fluorescence output upon induction by material precursor ions. Later, material-sensitive pairs were integrated into a modified curli nanofiber display biosystem to produce living autonomous whole cell nanomaterial synthesizers. These systems recognize precursor ions in the environment and synthesize modified curli nanofibers that can nuclate precursor ions to form functional nanomaterials.