Silicatein filaments and subunits from a marine sponge direct the polymerization of silica and silicones in vitro

Nanoscale control of the polymerization of silicon and oxygen determines th e structures and properties of a wide range of siloxane-based materials, in cluding glasses, ceramics, mesoporous molecular sieves and catalysts, elast omers, resins, insulators, optical coatings, and photoluminescent polymers, In contrast to anthropogenic and geological syntheses of these materials t hat require extremes of temperature, pressure, or pH, living systems produc e a remarkable diversity of nanostructured silicates at ambient temperature s and pressures and at near-neutral pH, We show here that the protein filam ents and their constituent subunits comprising the axial cores of silica sp icules in a marine sponge chemically and spatially direct the polymerizatio n of silica and silicone polymer networks from the corresponding alkoxide s ubstrates in vitro, under conditions in which such syntheses otherwise requ ire either an acid or base catalyst. Homology of the principal protein to t he well known enzyme cathepsin L points to a possible reaction mechanism th at is supported by recent site-directed mutagenesis experiments. The cataly tic activity of the "silicatein" (silica protein) molecule suggests new rou tes to the synthesis of silicon-based materials.