Structural and Functional Analysis of Silica Forming Organic Matrices

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Diatom biosilica is an organic-inorganic hybrid material, and the organic components are believed to play a role in biomineral morphogenesis. The organic components can be divided into two groups. Firstly, the soluble components, which are molecules that are soluble in aqueous solution after complete demineralization, and secondly, the insoluble organic matrices, which remain insoluble after demineralization. The diatom Thalassiosira pseudonana contains three different types of insoluble organic matrices: chitin-based meshworks, organic microrings, and organic microplates. During the previous funding period we have investigated (i) the biochemical composition of organic microrings and microplates (collaboration with the Shevchenko group, SP-3), (ii) the structure and assembly mechanism of the insoluble organic microrings (collaboration with the Schlierf group, SP-5), and (iii) the reconstitution of silica morphogenesis using soluble components and insoluble organic matrices. This lead to the identification of cingulin-like as well as novel organic matrix proteins, and revealed the low pH-induced assembly of mixed cingulin clusters and their silica precipitation activities. Remarkably, our experiments also demonstrated the feasibility to reconstitute diatom-like hierarchically porous silica patterns in vitro using soluble components and insoluble organic matrices from Cyclotella cryptica.In the new funding period, we will focus on studying the enigmatic self-assembly process that leads to formation of the hierarchically porous silica patterns in vitro, and aim to elucidate the underlying molecular mechanism. This will be approached using protein fractionation and characterization (collaboration with the Shevchenko group, SP-3), super-resolution fluorescence microscopy (collaboration with the Schlierf group, SP-5), and the generation of fluorescent protein-tagged organic components through molecular genetics. These in vitro analyses will reveal biomolecules and biomolecular interactions that are relevant for biosilica morphogenesis in diatoms.