Search results for "Uber"
showing 10 items of 1027 documents
Hardening of bio-silica in sponge spicules involves an aging process after its enzymatic polycondensation: evidence for an aquaporin-mediated water a…
2011
Abstract Background Spicules, the siliceous skeletal elements of the siliceous sponges, are synthesized enzymatically via silicatein. The product formed, bio-silica, constitutes their inorganic matrix. It remained unexplored which reactions are involved in molding of the amorphous bio-silica and formation of a solid and rigid biomaterial. Methods Cell and molecular biological techniques have been applied to analyze processes resulting in the hardening of the enzymatically synthesized bio-silica. The demosponge Suberites domuncula has been used for the studies. Results Cell aggregates (primmorphs) from the sponge S . domuncula , grown in the presence of Mn-sulfate, form spicules that compris…
Sponge biosilica formation involves syneresis following polycondensation in vivo.
2011
Syneresis is a process observed during the maturation/aging of silica gels obtained by sol-gel synthesis that results in shrinkage and expulsion of water due to a rearrangement and increase in the number of bridging siloxane bonds. Here we describe how the process of biosilica deposition during spicule ("biosilica" skeleton of the siliceous sponges) formation involves a phase of syneresis that occurs after the enzyme-mediated polycondensation reaction. Primmorphs from the demosponge Suberites domuncula were used to study syneresis and the inhibition of this mechanism. We showed by scanning electron microscopy that spicules added to primmorphs that have been incubated with manganese sulfate …
Selenium affects biosilica formation in the demosponge Suberites domuncula
2005
Selenium is a trace element found in freshwater and the marine environment. We show that it plays a major role in spicule formation in the demosponge Suberites domuncula. If added to primmorphs, an in vitro sponge cell culture system, it stimulates the formation of siliceous spicules. Using differential display of transcripts, we demonstrate that, after a 72-h exposure of primmorphs to selenium, two genes are up-regulated; one codes for selenoprotein M and the other for a novel spicule-associated protein. The deduced protein sequence of selenoprotein M (14 kDa) shows characteristic features of metazoan selenoproteins. The spicule-associated protein (26 kDa) comprises six characteristic repe…
Evagination of Cells Controls Bio-Silica Formation and Maturation during Spicule Formation in Sponges
2011
The enzymatic-silicatein mediated formation of the skeletal elements, the spicules of siliceous sponges starts intracellularly and is completed extracellularly. With Suberites domuncula we show that the axial growth of the spicules proceeds in three phases: (I) formation of an axial canal; (II) evagination of a cell process into the axial canal, and (III) assembly of the axial filament composed of silicatein. During these phases the core part of the spicule is synthesized. Silicatein and its substrate silicate are stored in silicasomes, found both inside and outside of the cellular extension within the axial canal, as well as all around the spicule. The membranes of the silicasomes are inte…
Localization and Characterization of Ferritin in Demospongiae: A Possible Role on Spiculogenesis
2014
Iron, as inorganic ion or as oxide, is widely used by biological systems in a myriad of biological functions (e.g., enzymatic, gene activation and/or regulation). In particular, marine organisms containing silica structures—diatoms and sponges—grow preferentially in the presence of iron. Using primary sponge cell culture from S. domuncula–primmorphs—as an in vitro model to study the Demospongiae spiculogenesis, we found the presence of agglomerates 50 nm in diameter exclusively inside sponge specialized cells called sclerocytes. A clear phase/material separation is observed between the agglomerates and the initial stages of intracellular spicule formation. STEM-HRTEM-EDX analysis of the agg…
Silicateins - A Novel Paradigm in Bioinorganic Chemistry: Enzymatic Synthesis of Inorganic Polymeric Silica
2013
The inorganic matrix of the siliceous skeletal elements of sponges, that is, spicules, is formed of amorphous biosilica. Until a decade ago, it remained unclear how the hard biosilica monoliths of the spicules are formed in sponges that live in a silica-poor (<50 mu m) aquatic environment. The following two discoveries caused a paradigm shift and allowed an elucidation of the processes underlying spicule formation; first the discovery that in the spicules only one major protein, silicatein, exists and second, that this protein displays a bio-catalytical, enzymatic function. These findings caused a paradigm shift, since silicatein is the first enzyme that catalyzes the formation of an inorga…
Identification of a silicatein(-related) protease in the giant spicules of the deep-sea hexactinellid Monorhaphis chuni.
2008
SUMMARYSilicateins, members of the cathepsin L family, are enzymes that have been shown to be involved in the biosynthesis/condensation of biosilica in spicules from Demospongiae (phylum Porifera), e.g. Tethya aurantium and Suberites domuncula. The class Hexactinellida also forms spicules from this inorganic material. This class of sponges includes species that form the largest biogenic silica structures on earth. The giant basal spicules from the hexactinellids Monorhaphis chuni and Monorhaphis intermedia can reach lengths of up to 3 m and diameters of 10 mm. The giant spicules as well as the tauactines consist of a biosilica shell that surrounds the axial canal, which harbours the axial f…
The silicatein propeptide acts as inhibitor/modulator of self-organization during spicule axial filament formation.
2013
Silicateins are crucial enzymes that are involved in formation of the inorganic biosilica scaffold of the spicular skeleton of siliceous sponges. We show that silicatein acquires its structure-guiding and enzymatically active state by processing of silicatein from pro-silicatein to the mature enzyme. A recombinant propeptide (PROP) of silicatein from the siliceous demosponge Suberites domuncula was prepared, and antibodies were raised against the peptide. In sponge tissue, these antibodies reacted with both surface structures and the central region of the spicules. Using phage display expression, spicule-binding 12-mer peptides were identified that are rich in histidine residues. In the pre…
Involvement of aquaporin channels in water extrusion from biosilica during maturation of sponge siliceous spicules.
2015
Aquaporins are a family of small, pore-forming, integral cell membrane proteins. This ancient protein family functions as water channels and is found in all kingdoms (including archaea, eubacteria, fungi, plants, and animals). We discovered that in sponges aquaporin plays a novel role during the maturation of spicules, their skeletal elements. Spicules are synthesized enzymatically via silicatein following a polycondensation reaction. During this process, a 1:1 stoichiometric release of water per one Si-O-Si bond formed is produced. The product of silicatein, biosilica, is a fluffy, soft material that must be hardened in order to function as a solid rod. Using the model of the demosponge sp…
Biosilica formation in spicules of the sponge Suberites domuncula: synchronous expression of a gene cluster.
2005
The formation of spicules is a complicated morphogenetic process in sponges (phylum Porifera). The primmorph system was used to demonstrate that in the demosponge Suberites domuncula the synthesis of the siliceous spicules starts intracellularly and is dependent on the concentration of silicic acid. To understand spicule formation, a cluster of genes was isolated. In the center of this cluster is the silicatein gene, which codes for the enzyme that synthesizes spicules. This gene is flanked by an ankyrin repeat gene at one side and by a tumor necrosis factor receptor-associated factor and a protein kinase gene at the other side. All genes are strongly expressed in primmorphs and intact anim…