A Spectroscopic and Computational Structure-Function Study of Biosilicification Peptides

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Metal oxides including silicon oxide (SiO2, silica) and titanium oxide (TiO2, titania) have numerous applications as insulators, textile coatings, catalysts, chemical decontaminants, solar cell components, medical/dental implants and chemical sensors. Industrial synthesis and morphological control of these important hard materials requires extremes in temperature, pressure and pH and are thus energetically demanding. In contrast, biological organisms accomplish impressive feats of mineral oxide production with precise control over morphology that is virtually unmatched by industrial approaches, and do so at ambient temperature, pressure and at physiological pH in a process called biomineralization. Biogenic silica (i.e. biosilica) is produced in gigaton quantities annually by the diatom, a marine microalgae characterized by an intricately decorated cell wall that is composed of organic material and silica. Diatoms take in silicon in dissolved form, and convert it to elaborate silica structures, in an as yet poorly understood process where proteins and other organic polymers are believed play important roles as catalysts and templates for silica formation. This research is aimed at understanding the specific roles played by proteins that are used by diatoms to form silica, with the immediate goal of making smaller, and less expensive molecules that imitate the diatom's ability to control silica formation under mild conditions. The long-term goal is to use similarly designed small molecules to effect the controlled formation of non-biological oxides like TiO2. This project will provide training for young scientists and engineers in the use of spectroscopic and computational techniques to elucidate structure-function relationships in biomaterials.The research will utilize solid state NMR (ssNMR), advanced non-equilibrium molecular dynamics (MD) computations, and novel chemical synthesis techniques, to determine the molecular structural properties and interactions that underlie the silicifying activities of naturally-occurring peptides. Initial study will be focused on modified and unmodified forms of the R5 peptide, derived from the bio-silicification protein silaffin of the diatom species Cylindrotheca fusiformis. Specific questions that this research project will address include: 1. Do unmodified silicifying peptide domain derived (e.g. R5) assume specific secondary structures that promote peptide-peptide interactions which in turn lead to formation of higher order structures? 2. What is the nature of peptide-silica interactions? 3. How do amino acid modifications influence peptide structure and peptide-peptide interactions in silica, and, most importantly, how do these modifications affect peptide-silica interactions? 4. Can R5, that induce silica formation, also induce formation of non-biological oxides like TiO2. Are the structural principles used by R5 to form silica similar to the principles it uses to form other oxides? Answers to these questions will provide structure-based principles for the design of peptides and other small molecules that can mimic in vitro the silicifying activities of naturally occurring proteins like silaffin.