Axial Filament of Silicious Sponge Spicules, Its Organic Components and Synthesis

Shore, Richard E.

doi:10.2307/1540191

Cited by 37 publications

(28 citation statements)

References 9 publications

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“…Because the axial protein filament is occluded wholly within the silica spicule, it had long been suspected of participating in the control of biosilicification, although the mechanism by which it might do so remains unclear (24). Hecky et al (4) postulated that the hydroxyl-rich proteins of the silicified diatom wall might condense with silicic acid monomers, thus serving as scaffolds to organize the growth of the silica.…”

Section: Discussionmentioning

confidence: 99%

Silicatein filaments and subunits from a marine sponge direct the polymerization of silica and silicones in vitro

Jennifer

Shimizu

Zhou

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

784

780

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Nanoscale control of the polymerization of silicon and oxygen determines the structures and properties of a wide range of siloxane-based materials, including glasses, ceramics, mesoporous molecular sieves and catalysts, elastomers, resins, insulators, optical coatings, and photoluminescent polymers. In contrast to anthropogenic and geological syntheses of these materials that require extremes of temperature, pressure, or pH, living systems produce a remarkable diversity of nanostructured silicates at ambient temperatures and pressures and at near-neutral pH. We show here that the protein filaments and their constituent subunits comprising the axial cores of silica spicules in a marine sponge chemically and spatially direct the polymerization of silica and silicone polymer networks from the corresponding alkoxide substrates in vitro, under conditions in which such syntheses otherwise require either an acid or base catalyst. Homology of the principal protein to the well known enzyme cathepsin L points to a possible reaction mechanism that is supported by recent site-directed mutagenesis experiments. The catalytic activity of the ''silicatein'' (silica protein) molecule suggests new routes to the synthesis of silicon-based materials.Silicon, the second most abundant element in the earth's crust, interacts with living systems by mechanisms that have remained poorly understood (1-6). Evidence suggests that silicon is essential for normal growth and biological function in a diversity of plant, animal, and microbial systems (2); silicon compounds have been shown to modulate these activities (1, 2), but the molecular mechanisms of these effects have proved elusive. Studies of marine organisms that produce relatively large masses of silicified structures (3) show the underlying molecular and genetic mechanisms by which living systems process silicon. Hildebrand et al. (7) recently characterized the cDNAs coding for a family of silicon transporters in diatoms and showed that the transporters are likely transmembrane proteins. We have found that the marine sponge Tethya aurantia produces copious silica spicules (1-2 mm in length and 30 m in diameter) that constitute 75% of the dry weight of the organism and that each of these spicules contains a central axial filament of protein (1-2 mm in length and 2 m in diameter) consisting of three very similar subunits that we have named silicateins (for silica proteins; ref. 8). Characterization of silicatein ␣ (the subunit comprising nearly 70% of the mass of the filaments) and its cloned cDNA indicated that it is homologous to members of the cathepsin L subfamily of the papain family of proteolytic enzymes (8).We show here that, at neutral pH, the silicatein filaments and their constituent subunits catalyze the in vitro polymerization of silica and silsesquioxanes from tetraethoxysilane and organically modified silicon triethoxides, respectively. These substrates were chosen because of their stability at neutral pH and the similarity of their chemical reactivity to that of...

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Section: Discussionmentioning

confidence: 99%

Silicatein filaments and subunits from a marine sponge direct the polymerization of silica and silicones in vitro

Jennifer

Shimizu

Zhou

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

784

780

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“…Furthermore, the cross section of the spicules in Fig. 4B shows a solid structure around the channel, whereas other sponges have a layered structure (Aizenberg et al, 2004;Levi et al, 1989;Shore, 1972;Uriz et al, 2000). To investigate the chemical nature of the junctions, spicules subjected to bleaching and heattreatment at 823 K are considered.…”

Section: Macroscopic Structure Of the Spongementioning

confidence: 99%

Microscopic Features of Biologically Formed Amorphous Silica

Jensen¹,

Keding²,

Yue³

2011

On Biomimetics

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“…Siliceous spicules of demosponges are known to contain an axial filament composed of protein (Shore 1972). However, the mechanism of spicule formation had remained unclear until studies in two demosponges, Tethya aurantium Cha et al 2000;Shimizu et al 1998) and Suberites domuncula (Krasko et al 2000), revealed that the axial filament of siliceous spicule was enzymatically fabricated via a protein called silicatein.…”

Section: Spicule Formationmentioning

confidence: 99%

“…Spicule development and morphology have been characterised since the early 1900s (Bergquist and Sinclair 1973;Borojevic et al 1968;Schulze 1904;Shore 1972;Simpson 1984).…”

Section: Introductionmentioning

confidence: 99%

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Analysis of silicatein gene expression and spicule formation in the demosponge Amphimedon queenslandica

Gauthier¹

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The skeletal elements in most sponges are siliceous spicules. These are fabricated into species-specific sizes and shapes. Demosponges, in particular, have specialised cells called sclerocytes that possess the unique ability to synthesise biosilica and these spicules.Underlying the diversity of demosponge spicules morphology is a conserved protein, called silicatein. This thesis aims to investigate the process of spiculogenesis in the different developmental stages of the demosponge Amphimedon queenslandica, and the evolution and developmental expression of the silicatein gene family in relation to spicule formation.A. queenslandica is the only sponge species to have its genome fully sequenced, assembled and annotated, and currently is one of the best models to study sponge development (Srivastava et al. 2010). This species broods embryos year-round, facilitating the access to Conservation of gene structure and exon length in silicatein and cathepsin L genes suggests that these genes have preserved an ancestral gene structure common to both gene families in both marine and freshwater sponges.Using in situ hybridisation, I demonstrated that silicatein genes are expressed during A. queenslandica early embryonic development, with genes being expressed exclusively in sclerocytes. Analysis of gene expression levels through embryogenesis and metamorphosis, using RNA-Seq performed on a pool of same stage individuals, revealed that all silicatein-like genes are differentially expressed throughout development, and the expression of silicatein genes occurs prior to spicule formation. However, some silicatein-like gene expression levels and spicule number do not appear to be tightly correlated.

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Axial Filament of Silicious Sponge Spicules, Its Organic Components and Synthesis

Cited by 37 publications

References 9 publications

Silicatein filaments and subunits from a marine sponge direct the polymerization of silica and silicones in vitro

Silicatein filaments and subunits from a marine sponge direct the polymerization of silica and silicones in vitro

Microscopic Features of Biologically Formed Amorphous Silica

Analysis of silicatein gene expression and spicule formation in the demosponge Amphimedon queenslandica

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