Silicateins play a key role in biosynthesis of spicules in marine sponges; they are also capable to catalyze formation of amorphous silica in vitro. Silicateins are highly homologous to cathepsins L - a family of cysteine proteases. Molecular mechanisms of silicatein activity remain controversial. Here site-directed mutagenesis was used to clarify significance of selected residues in silica polymerization. A number of mutations were introduced into two sponge proteins - silicatein A1 and cathepsin L from Latrunculia oparinae, as well as into human cathepsin L. First direction was alanine scanning of the proposed catalytic residues. Also, reciprocal mutations were introduced at selected positions that differ between cathepsins L and silicateins. Surprisingly, all the wild type and mutant proteins were capable to catalyze amorphous silica formation with a water-soluble silica precursor tetra(glycerol)orthosilicate. Some mutants possessed several-fold enhanced silica-forming activity and can potentially be useful for nanomaterial synthesis applications. Our findings contradict to the previously suggested mechanisms of silicatein action via a catalytic triad analogous to that in cathepsins L. Instead, a surface-templated biosilification by silicateins and related proteins can be proposed.

中文翻译：

---

用组织蛋白酶和硅酸盐样蛋白从原硅酸四甘油酯高效合成二氧化硅。

硅酸盐素在海洋海绵中的针状生物的合成中起着关键作用。它们还能够在体外催化无定形二氧化硅的形成。Silicateins与组织蛋白酶L（半胱氨酸蛋白酶家族）高度同源。硅酸盐活性的分子机制仍存在争议。在此使用定点诱变来阐明二氧化硅聚合反应中所选残基的重要性。许多突变被引入到两个海绵蛋白中—硅酸单胞菌素A1和不透明脂肪杆菌的组织蛋白酶L，以及人组织蛋白酶L。第一个方向是丙氨酸扫描拟议的催化残基。而且，在组织蛋白酶L和硅酸盐素之间不同的选定位置处引入了相互的突变。出奇，所有的野生型和突变蛋白都能够催化水溶性二氧化硅前体原硅酸四（甘油）酯形成无定形二氧化硅。一些突变体具有提高数倍的二氧化硅形成活性，并且可能潜在地用于纳米材料合成应用。我们的发现与先前建议的通过组织三聚体L中催化三联体作用的硅酸酯作用机理相反。相反，可以提出通过硅酸酯和相关蛋白进行表面模板化的生物硅化反应。