Manchester Institute of Biotechnology, University of Manchester, Manchester M1 7DN, United Kingdom.
School of Chemistry, University of Manchester, Manchester M13 9PL, United Kingdom.
Proc Natl Acad Sci U S A. 2017 Jul 3;114(27):E5285-E5291. doi: 10.1073/pnas.1613320114. Epub 2017 Jun 19.
The family of silicatein enzymes from marine sponges (phylum Porifera) is unique in nature for catalyzing the formation of inorganic silica structures, which the organisms incorporate into their skeleton. However, the synthesis of organosiloxanes catalyzed by these enzymes has thus far remained largely unexplored. To investigate the reactivity of these enzymes in relation to this important class of compounds, their catalysis of Si-O bond hydrolysis and condensation was investigated with a range of model organosilanols and silyl ethers. 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 / values on the order of 2-50 min μM 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 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 efficient and selective biocatalysts for organosiloxane chemistry.
海洋海绵（多孔动物门）中的硅蛋白酶家族在自然界中是独一无二的，因为它们能够催化无机硅质结构的形成，而生物体则将这些结构纳入其骨架中。然而，这些酶催化的有机硅氧烷的合成迄今为止在很大程度上仍未得到探索。为了研究这些酶与这一类重要化合物的反应性，研究人员用一系列模型有机硅烷醇和硅醚研究了它们对 Si-O 键水解和缩合的催化作用。通过基于 4-硝基苯硅醚水解的高通量比色测定法获得了这些酶的动力学参数。这些测定法清楚地表明，酶具有明显的催化作用，/ 值在 2-50 min μM 之间。缩合反应也通过相应的硅醇和醇生成硅醚得到证明。值得注意的是，当酶遇到同时具有脂肪族和芳香族羟基的底物时，它优先硅烷化后者，这与非酶硅烷化形成鲜明对比。此外，硅蛋白还能够催化转醚化反应，其中一个硅醚中的硅基可以转移到受体醇上。尽管与蛋白酶组织蛋白酶 L 具有密切的序列同源性，但在针对类似底物进行测试时，硅蛋白似乎没有表现出明显的蛋白酶或酯酶活性。总的来说，这些结果表明，硅蛋白是未来用于有机硅氧烷化学的高效和选择性生物催化剂的有前途的候选者。
