The silicatein enzymes from marine sponges (phylum Porifera) are unique in nature for catalyzing the formation of inorganic silica structures, which the organisms incorporate into their skeleton. However, it has more recently been shown that these enzymes are also able to catalyse the hydrolysis and condensation of Si–O bonds in organosilicon compounds, which suggest potential applications in the synthetic manipulation of this economically important class of compounds. In order to explore the properties and substrate scope of this enzyme, a range of biophysical measurements and enzyme assays were carried out. The enzymes’ kinetic parameters were obtained by a high-throughput colorimetric assay based on the hydrolysis of 4-nitrophenyl silyl ethers. These assays showed unambiguous catalysis with kcat/Km values on the order of 2–50 min–1 μM–1. Condensation reactions were also demonstrated by the generation of silyl ethers from their corresponding silanols and alcohols. Notably, when presented with a substrate bearing both aliphatic and aromatic hydroxy groups the enzyme preferentially silylates the latter group, in clear contrast to nonenzymatic silylations. Furthermore, the silicateins are able to catalyze transetherifications, where the silyl group from one silyl ether may be transferred to a recipient alcohol. Despite their close sequence homology to the protease cathepsin L, the silicateins seem to exhibit no significant protease or esterase activity when tested against analogous substrates. Overall, these results suggest the silicateins are promising candidates for future elaboration into selective biocatalysts for organosiloxane chemistry.

Exploring silicateins for the biocatalysis of organosiloxane chemistry

2019 Fall National Meeting

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