FIBER DIFFRACTION STUDIES OF THE SILICATEIN PROTEIN FILAMENT

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。我们建议对硅蛋白细丝进行纤维衍射研究。这些蛋白质纤维（直径约2微米，长度约2毫米）被发现封闭在由Tethya aurantia海绵制成的二氧化硅针状针状体中。我们的实验室发现，这些细丝是由三种相关的蛋白质组成的，我们将其命名为硅酸盐蛋白，它们是组织蛋白酶/催化三超家族水解酶的成员。在体外，他们催化和模板从相应的分子前体合成二氧化硅、有机硅和半导体（如氧化镓、二氧化钛、氧化锌等）。此外，在常温和常压下，二氧化钛和Ga2O3产物是多晶型的，其形成通常需要极端的温度、pH和压力条件。重要的是，这些涂层是纳米晶体的，这表明长丝可能稳定和模板化无机产品。由于几个原因，解决硅蛋白纤维的纤维衍射在科学上是有趣的。首先，它们作为模板来指导它们通过催化形成的矿物质（如Ga2O3）的纳米结构——因此代表了我们所知道的一类真正的结构指导酶的第一个实例。我们希望通过了解蛋白质在长丝内的堆积和周期性，我们将能够描述无机产物模板化和伪外延稳定的分子决定因素。我们已经在蛋白质纤维中看到了晶体样周期性的证据（通过低分辨率衍射）；同步加速器光源提供的额外分辨率将大大扩展我们对灯丝结构的认识。

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.