Silicatein is the main protein responsible for the formation of spicules, tiny structures that constitute the silica skeleton of marine demosponges (Phylum Porifera). A unique innovation in Porifera that evolved from the cathepsin L family of proteins, it has been reported that two amino acids (S and H) are necessary to form the catalytic triad (SHN) to enable silica condensation. However, a diversity of silicatein sequence variants has since been reported with a variable pattern of presence/absence across sponge groups. Variants containing CHN or C/SQN at the active site appear more common in sponges from the Haplosclerida. Here, we report the expression levels of five silicatein variants through different developmental stages in the haplosclerid Haliclona indistincta. All five silicatein variants were expressed at low levels in the free-swimming larvae, which lack spicules and expression significantly increased at the two developmental phases in which spicules were visible. At these two phases, silicateins of CHN and C/SQN types were much more highly expressed than the SHN type indicating a possible ability of active sites with these alternative amino acids to condense silica and a more complex evolutionary story for spicule formation in marine demosponges than previously understood.

中文翻译：

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硅藻素在不同发育阶段在无形拟青霉（Phylum Porifera，Order Haplosclerida）中的表达。

硅酸盐是构成针状体的主要蛋白质，针状体是构成海洋海绵（Phylum Porifera）的二氧化硅骨架的微小结构。从组织蛋白酶L家族蛋白质进化而来的Porifera的一项独特创新，据报道，两个氨基酸（S和H）对于形成催化三联体（SHN）以实现二氧化硅缩合是必需的。然而，自那以后，已经报道了多种硅酸盐序列变异体，其在海绵基团之间存在/不存在的变化模式。活性部位中含有CHN或C / SQN的变体似乎在单倍体海绵中更常见。在此，我们表示5个silicatein的表达水平，通过在haplosclerid不同发育阶段的变种Haliclona indistincta。在自由游动的幼虫中，所有五个硅酸盐蛋白变体均以低水平表达，它们缺乏针状体，并且在两个可见于针状体的发育阶段的表达显着增加。在这两个阶段，CHN和C / SQN类型的硅酸盐比SHN类型的表达高得多，这表明具有这些替代氨基酸的活性位点可能具有凝结二氧化硅的能力，并且在海洋脱脂中形成针状物的过程更为复杂。以前了解。