This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We are proposing to perform fiber diffraction studies of the silicatein protein filament. These protein fibers (with dimensions of ~ 2 microns in diameter by 2 mm in length) are found occluded within the silica needle-like spicules made by the marine sponge Tethya aurantia. Our lab discovered that the filaments are composed of three related proteins that we named silicateins, which are members of the cathepsin/catalytic triad superfamily of hydrolases. In vitro, they catalyze and template the synthesis of silica, silicones, and semiconductors (such as gallium oxide, titanium dioxide, zinc oxide, etc.) from the corresponding molecular precursors. In addition, under ambient conditions, the resulting TiO2 and Ga2O3 products, formed in the presence of silicatein filaments at ambient temperature and pressure, are polymorphs whose formation usually requires extreme temperature, pH, and pressure conditions. Importantly, these coatings are nano-crystalline, suggesting the filament may be stabilizing and templating the inorganic products. Solving the fiber diffraction of the silicatein protein fibers is scientifically interesting for several reasons. First, they serve as templates to direct the nanostructures of the minerals (such as Ga2O3) they form by catalysis - thus representing the first instance of which we're aware of a class of truly structure-directing enzymes. We hope that by understanding the packing and periodicity of the proteins within the filament we will be able to describe the molecule determinants of templating and pseudo-epitaxial stabilization of the inorganic products. We have already seen evidence for a crystalline-like periodicity in the protein fibers (with low-resolution diffraction); the additional resolution provided by the synchrotron light-source should greatly expand our knowledge of the structure of the filament.
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