Schröder Heinz C, Boreiko Alexandra, Korzhev Michael, Tahir Muhammad N, Tremel Wolfgang, Eckert Carsten, Ushijima Hiroshi, Müller Isabel M, Müller Werner E G
Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität Mainz, Duesbergweg 6, D-55099 Mainz, Germany.
J Biol Chem. 2006 Apr 28;281(17):12001-9. doi: 10.1074/jbc.M512677200. Epub 2006 Feb 22.
Sponges (phylum Porifera) of the class of Demospongiae are stabilized by a siliceous skeleton. It is composed of silica needles (spicules), which provide the morphogenetic scaffold of these metazoans. In the center of the spicules there is an axial filament that consists predominantly of silicatein, an enzyme that catalyzes the synthesis of biosilica. By differential display of transcripts we identified additional proteins involved in silica formation. Two genes were isolated from the marine demosponge Suberites domuncula; one codes for a galectin and the other for a fibrillar collagen. The galectin forms aggregates to which silicatein molecules bind. The extent of the silicatein-mediated silica formation strongly increased if associated with the galectin. By applying a new and mild extraction procedure that avoids hydrogen fluoride treatment, native axial filaments were extracted from spicules of S. domuncula. These filaments contained, in addition to silicatein, the galectin and a few other proteins. Immunogold electron microscopic studies underscored the role of these additional proteins, in particular that of galectin, in spiculogenesis. Galectin, in addition to silicatein, presumably forms in the axial canal as well as on the surface of the spicules an organized net-like matrix. In the extraspicular space most of these complexes are arranged concentrically around the spicules. Taken together, these additional proteins, working together with silicatein, may also be relevant for potential (nano)-biotechnological applications of silicatein in the formation of surface coatings. Finally, we propose a scheme that outlines the matrix (galectin/silicatein)-guided appositional growth of spicules through centripetal and centrifugal synthesis and deposition of biosilica.
寻常海绵纲的海绵动物（多孔动物门）由硅质骨架支撑。该骨架由硅针（骨针）组成，为这些后生动物提供形态发生支架。在硅针的中心有一条轴向丝，主要由硅酸酶组成，硅酸酶是一种催化生物二氧化硅合成的酶。通过转录本差异显示，我们鉴定出了参与二氧化硅形成的其他蛋白质。从海洋海绵Suberites domuncula中分离出两个基因；一个编码半乳糖凝集素，另一个编码纤维状胶原蛋白。半乳糖凝集素形成聚集体，硅酸酶分子与之结合。如果与半乳糖凝集素结合，硅酸酶介导的二氧化硅形成程度会显著增加。通过采用一种避免氢氟酸处理的新型温和提取方法，从Suberites domuncula的硅针中提取出了天然轴向丝。这些丝除了含有硅酸酶外，还含有半乳糖凝集素和其他一些蛋白质。免疫金电子显微镜研究强调了这些额外蛋白质，特别是半乳糖凝集素在骨针形成中的作用。除硅酸酶外，半乳糖凝集素可能在轴向管以及硅针表面形成有组织的网状基质。在针外空间，这些复合物大多围绕硅针同心排列。总之，这些额外蛋白质与硅酸酶共同作用，可能也与硅酸酶在表面涂层形成中的潜在（纳米）生物技术应用相关。最后，我们提出了一个方案，概述了通过生物二氧化硅的向心和离心合成与沉积，由基质（半乳糖凝集素/硅酸酶）引导的骨针并置生长过程。
