Sensitivity Enhanced NMR and Real-time Monitoring of Biosilica Condensation Catalyzed by Silaffin Peptide

Yasmin Geiger, chemistry, BIU, Ramat-Gan, Israel
Hugo Gottlieb, chemistry, BIU, Ramat-Gan, Israel
Umit Akbey, NMR Supported Structural Biology, FMP, Berlin, Germany
Hartmut Oschkinat, NMR Supported Structural Biology, FMP, Berlin, Germany
Gil Goobes, chemistry, BIU, Ramat-Gan, Israel

Biosilicification is the formation and assembly of silica in living cells. This process is of great interest for marine biology research and is highly attractive for nanomaterial design, biomedical research and green chemistry. The silica-made cell wall of the diatom algae, with its complex nanometric design and structure, inspire biomimetic approaches to silica preparation. Previous studies indicate that a family of enzymes called silaffins is a key element in directing and controlling the biosilicification process in diatoms. It is believed that silaffins with phosphorylated groups and other polyamines form micelles which act as a template for silica precipitation. Recent research suggests that clusters of five lysine, termed pentalysine, along the sequence of silaffins, are the primary binding sites of the proteins to silica. Pentalysine segments were suggested to have greater contribution than a simple cumulative effect of their hydrogen bonds and positive charges. One such pentalysine containing peptide is the PL12 segment derived from the diatom T. Pseudonana silaffin.

We investigated the effect of PL12 on silica polymerization and characterized the organic-inorganic interface formed when they co-precipitate. The time course of silica precipitation was examined using electron microscopy and spectrophotometric measurements. The initial peptide and final product were analyzed using solution NMR, MAS NMR and DNP MAS NMR measurements. The recently-developed sensitivity-enhanced DNP method is utilized here for 2D NMR measurement on PL12-silica samples containing naturally low abundance ¹³C and ²⁹Si. The application of these methods permits us to characterize both the mineral bulk and surface and the peptide in solution and embedded in the silica.