Institute for Physiological Chemistry and Pathobiochemistry, Medical School, Johannes Gutenberg-University, Mainz, Germany.
J Struct Biol. 2009 Dec;168(3):548-61. doi: 10.1016/j.jsb.2009.08.003. Epub 2009 Aug 14.
The two sponge classes, Hexactinellida and Demospongiae, comprise a skeleton that is composed of siliceous skeletal elements (spicules). Spicule growth proceeds by appositional layering of lamellae that consist of silica nanoparticles, which are synthesized via the sponge-specific enzyme silicatein. While in demosponges during maturation the lamellae consolidate to a solid rod, the lamellar organization of hexactinellid spicules largely persists. However, the innermost lamellae, near the spicule core, can also fuse to a solid axial cylinder. Similar to the fusion of siliceous nanoparticles and lamella, in several hexactinellid species individual spicules unify during sintering-like processes. Here, we study the different stages of a process that we termed bio-sintering, within the giant basal spicule (GBS) of Monorhaphis chuni. During this study, a major GBS protein component (27 kDa) was isolated and analyzed by MALDI-TOF-MS. The sequences were used to isolate and clone the encoding cDNA via degenerate primer PCR. Bioinformatic analyses revealed a significant sequence homology to silicatein. In addition, the native GBS protein was able to mediate bio-silica synthesis in vitro. We conclude that the syntheses of bio-silica in M. chuni, and the subsequent fusion of nanoparticles to lamellae, and finally to spicules, are enzymatically-driven by a silicatein-like protein. In addition, evidence is now presented that in hexactinellids those fusions involve sintering-like processes.
这两个海绵类群，六放海绵纲和寻常海绵纲，由硅质骨骼元素（骨针）组成。骨针的生长通过硅质纳米颗粒的层状附加进行，这些纳米颗粒是通过海绵特异性酶硅蛋白合成的。在寻常海绵中，在成熟过程中，薄片层合并为固体棒，而六放海绵的薄片层组织在很大程度上保持不变。然而，靠近骨针核心的最内层薄片也可以融合成固体轴向圆柱体。类似于硅质纳米颗粒和薄片的融合，在几种六放海绵物种中，个体骨针在类似烧结的过程中统一。在这里，我们研究了我们称之为生物烧结的过程的不同阶段，在 Monorhaphis chuni 的巨大基骨针（GBS）中。在这项研究中，分离并通过 MALDI-TOF-MS 分析了一种主要的 GBS 蛋白成分（27 kDa）。使用这些序列通过简并引物 PCR 分离和克隆编码 cDNA。生物信息学分析显示出与硅蛋白显著的序列同源性。此外，天然的 GBS 蛋白能够在体外介导生物硅的合成。我们得出结论，M. chuni 中的生物硅合成以及随后的纳米颗粒到薄片层的融合，最后到骨针的融合，是由硅蛋白样蛋白酶促驱动的。此外，现在提出的证据表明，在六放海绵中，这些融合涉及类似烧结的过程。
