Biosilica formation

Various linear synthetic analogs of the natural active polyamines in biosilica formation on the basis of linear poly(ethylene imine) or polyfpropylene imine) were recently synthesized and reported to accelerate the silk acid condensation even more than the above-mentioned silaffins [226]. This imphes that it is not the silaffin protein superstructure that is responsible for its catalytic activity,as is the case for example in enzymes. In addition, poly(L-lysine) also led to modified silica morphologies such as fibers or ladders [227]. 

The complex morphology of the nanopatterned siUca diatom cell walls has been found to be related to species-specific sets of polycationic peptides, so-called silaffins, which were isolated from diatom cell walls [82], The morphologies of precipitated sihca can be controlled by changing the chain lengths of the polyamines as well as by a synergistic action of long-chain polyamines and silaffins [83,84]. It has been proposed that the delicate pattern formation in diatom shells can be explained by phase separation of silica solutions in the presence of these polyamines [85]. Various linear synthetic analogs of the natural active polyamines in biosilica formation can accelerate the silicic acid condensation even more than the above mentioned... 

The radial, appositional thickening of the spicnles and then the axial elongation process (Schroder et al., 2W6) was first nnderstood. In the extracellular space, the silicatein molecules are organized into larger entities, by concentric rings/cylinders around the spicule surface. These structures become stabiUzed by the protein galectin and Ca within these cylinders, the siUcatein-mediated biosilica formation occurs. In... 

Figure 2.4 Longitudinal growth of the spicules, (a and b) After the release of the immature spicule into the extracellular space via evagination of a cell protrusion, the growing spicule is pushed away from the cell (sclerocyte) that initially has formed the immature spicule (scheme). This process is driven by an elongation of the cell protrusion and in turn an elongation of the axial filament (af) within the axial canal. Again, it is highlighted that sihca deposition occurs within the axial canal and onto the surface of the spicules. Around the spicules, silicasomes (sis) exist, which release silicatein and orthosilicate to allow biosilica formation to occur, (c) A protruding axial canal (ac) is shown that harbors an axial filament (d) Silica shell around the axial canal/axial filament (af). (e) A liberated axial filament (af) projecting from a spicule.

SchloBmacher, U., Wiens, M., Schroder, H.C., Wang, X.H., Jochum, K.P., Miiller, W.E.G., 2011. Silintaphin-1 interaction with sUicatein during structure guiding biosilica formation. FEES J. 278, 1145-1155. 

Poulsen, N., Sumper, M. and Kroger, N. (2003) Biosilica formation in diatoms characterization of native silaffin-2 and its role in silica morphogenesis. 

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