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

TLDR

Nanoscale control of silicon‑oxygen polymerization determines the structures of siloxane materials, and living systems can produce diverse nanostructured silicates at ambient temperatures, pressures, and near‑neutral pH, unlike harsh anthropogenic processes. The study demonstrates that marine sponge silicatein filaments and subunits direct silica and silicone polymerization from alkoxide substrates in vitro without the need for external acid or base catalysts. Silicatein’s similarity to the enzyme cathepsin L suggests a catalytic mechanism that is supported by recent site‑directed mutagenesis experiments. The catalytic activity of silicatein opens new routes for synthesizing silicon‑based materials.

Abstract

Nanoscale control of the polymerization of silicon and oxygen determines the structures and properties of a wide range of siloxane-based materials, including glasses, ceramics, mesoporous molecular sieves and catalysts, elastomers, resins, insulators, optical coatings, and photoluminescent polymers. In contrast to anthropogenic and geological syntheses of these materials that require extremes of temperature, pressure, or pH, living systems produce a remarkable diversity of nanostructured silicates at ambient temperatures and pressures and at near-neutral pH. We show here that the protein filaments and their constituent subunits comprising the axial cores of silica spicules in a marine sponge chemically and spatially direct the polymerization of silica and silicone polymer networks from the corresponding alkoxide substrates in vitro , under conditions in which such syntheses otherwise require either an acid or base catalyst. Homology of the principal protein to the well known enzyme cathepsin L points to a possible reaction mechanism that is supported by recent site-directed mutagenesis experiments. The catalytic activity of the “silicatein” ( silica pro tein ) molecule suggests new routes to the synthesis of silicon-based materials.