Silicateins, the major biosilica forming enzymes present in demosponges:: Protein analysis and phylogenetic relationship
Silicateins, the major biosilica forming enzymes present in demosponges:: Protein analysis and phylogenetic relationship
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DOI：
10.1016/j.gene.2007.02.014
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发表时间：
2007-06-15
期刊：
影响因子：
3.5
通讯作者：
Schroeder, Heinz C.
中科院分区：
文献类型：
--
作者：
Mueller, Werner E. G.;Boreiko, Alexandra;Schroeder, Heinz C.
硅酸盐是仅限于海绵（多孔菌门）的酶，介导单体硅化合物催化形成生物二氧化硅。硅酸盐蛋白被分隔在位于硅质骨针的轴向管中的轴向丝的海绵中。在本研究中，硅酸蛋白已从淡水海绵 Lubomirskia baicalensis 中分离出来，其异构体大小为 23 kDa、24 kDa 和 26 kDa。由于较大的蛋白质被糖基化，我们推测它是较小尺寸形式之一的加工形式。硅酸盐异构体通过磷酸化进行翻译后修饰；至少存在四种同工型，PL 为5.4、5.2、4.9 和4.7。令人惊讶的是，硅酸盐不仅介导硅酸盐的聚合，而且还表现出组织蛋白酶L酶特有的蛋白水解活性，从而强调了硅酸盐与组织蛋白酶L的高度相关性。克隆了来自黄芩的硅酸盐和组织蛋白酶L的cDNA以及各自的基因。研究发现，海绵基因中存在的五个内含子对于人类组织蛋白酶 L 来说是高度保守的。该分析是通过对两个硅酸盐基因（均为硅酸盐-α 和 -β）和来自另一种海绵海绵（Suberites domunula）的组织蛋白酶 L 进行测序而完成的。对这些新序列进行的全面系统发育分析为发生在后生动物门底部的组织蛋白酶 L 和硅酸盐家族的进化提供了新的线索。结论是，与这些酶的出现同时，内含子的数量首先增加，特别是在成熟酶的编码区。在进化的后期，内含子的数量再次减少。我们假设催化三联体的修饰，尤其是其第一个氨基酸的修饰，是化学调节硅酸盐/组织蛋白酶 L 酶功能的合适目标。(C) 2007 Elsevier B.V. 保留所有权利。
Silicateins are enzymes, which are restricted to sponges (phylum Porifera), that mediate the catalytic formation of biosilica from monomeric silicon compounds. The silicatein protein is compartmented in the sponges in the axial filaments which reside in the axial canals of the siliceous spicules. In the present study silicatein has been isolated from the freshwater sponge Lubomirskia baicalensis where it occurs in isoforms with sizes of 23 kDa, 24 kDa and 26 kDa. Since the larger protein is glycosylated we posit that it is a processed form of one of the smaller size forms. The silicatein isoforms are post-translationally modified by phosphorylation; at least four isoforms exist with pl's of 5.4, of 5.2, of 4.9 and of 4.7. Surprisingly silicatein not only mediates polymerization of silicate, but also displays proteolytic activity which is specific for cathepsin L enzymes, thus underscoring the high relationship of the silicateins to cathepsin L. The cDNAs fi-om L. baicalensis for silicatein and cathepsin L, as well as the respective genes, were cloned. It was found that the five introns present in the sponge genes are highly conserved up to human cathepsin L. This analysis has been completed by sequencing of two silicatein genes (both for silicatein-alpha and -beta) and of cathepsin L from another demosponge, Suberites domuncula. A comprehensive phylogenetic analysis with these new sequences shed new light upon the evolution of cathepsin L and silicatein families which occurred at the base of the metazoan phyla. It is concluded, that in parallel with the emergence of these enzymes at first the number of introns increased, especially in the coding region of the mature enzyme. Later in evolution the number of introns decreased again. We postulate that modification of the catalytic triad, especially of its first amino acid, is a suitable target for a chemical modulation of enzyme function of the silicateins/cathepsin L. (C) 2007 Elsevier B.V. All rights reserved.