Biosilica

Kroger N, Deutzmann R, Sumper M (1999) Polycationic peptides from diatom biosilica that direct silica nanosphere formation. Science 286 1129-1132... 

The strong interest in biomineralization is due to its high effidency and the superiority of the properties of biosilica over those of silica fabricated in geological processes and industrially. It proceeds at mild, ambient conditions in... 

Shimizu, K., Cha, J., Stucky, G.D. and Morse, D.E. (1998) Silicatein alpha Cathepsin L-like protein in sponge biosilica. Proceedings of the National Academy of Sciences of the United States of America, 95, 6234-6238. 

Swift, D.M. and Wheeler, A.P. (1992) Evidence of an organic matrix from diatom biosilica. Journal of Phycology, 28, 202-209. 

Kroger, N., Lorenz, S., Brunner, E. and Sumper, M. (2002) Self-assembly of highly phosporylated silaffins and their function in biosilica morphogenesis. Science, 298, 584-586. 

Some non-silica sol-gel materials have also been developed to immobilize bioactive molecules for the construction of biosensors and to synthesize new catalysts for the functional devices. Liu et al. [33] proved that alumina sol-gel was a suitable matrix to improve the immobilization of tyrosinase for detection of trace phenols. Titania is another kind of non-silica material easily obtained from the sol-gel process [34, 35], Luckarift et al. [36] introduced a new method for enzyme immobilization in a bio-mimetic silica support. In this biosilicification process precipitation was catalyzed by the R5 peptide, the repeat unit of the silaffin, which was identified from the diatom Cylindrotheca fusiformis. During the enzyme immobilization in biosilicification the reaction mixture consisted of silicic acid (hydrolyzed tetramethyl orthosilicate) and R5 peptide and enzyme. In the process of precipitation the reaction enzyme was entrapped and nm-sized biosilica-immobilized spheres were formed. Carturan et al. [11] developed a biosil method for the encapsulation of plant and animal cells. 

The activities of the purple fluid of the sea hare Aplysia dactylomela, such as toxic, antimicrobial and hemagglutinating properties, have been attributed to a substance of protein nature [332], Proteoglycans and adhesive glycoproteins present in the extracellular matrix of vertebrates, have also been reported in sponges. These molecules are probably involved in the cell adhesion systems of sponges [333], Recently, novel marine proteins have been reported, such as silicatein from sponge biosilica [334], and a metallothionein protein from the marine alga Fuats vesiculosus [335], Metallothioneins have also been isolated from Arctic... 

B. Polycationic Peptides Occluded in Diatom Biosilica Accelerate Silicic... 

FIGURE 1. The lysine family of cationic amino acids. Structures include the typical a-amino acid found in proteins, and the cationic side-chains of lysine, arginine and the two substituted lysine derivatives recently found in high abundance in the silaffins occluded within the biosilica of a diatom35. The derivatives with multiple methylaminopropyl units were previously unknown in biological systems... 

Within seconds after their addition to dilute silicic acid, the silaffins induce co-precipita-tion of silica nanospheres35. Rates of formation of the nanoparticles are rapid and constant from pH 5 to pH 7 the precipitates form stoichiometrically with the silaffins, which become occluded within the silica. The nanoparticles produced in vitro are comparable in dimension to those that have been observed in the developing biosilica in diatoms36 37, as well as those revealed by differential etching of the biosilica produced by sponges38. 

C. Silicateins Structure-Directing, Polycondensation-Catalyzing Proteins from Sponge Biosilica... 

R. Wetherbee, S. Crawford, and P. Mulvaney, The Nanostructure and Development of Diatom Biosilica, in Biomineralization, from Biology to Biotechnology and Medical Application , ed. E. Baeuerlein, Wdey-VCH, Weinheim, 2000, p. 189. 

Wetherbee R., Crawford S., and Mulvaney P. (2000) The nanostructure and development of diatom biosilica. In Biomineralization (ed. E. Baeuerlein). Wiley, Weinheim, Germany, pp. 189-206. 

As demonstrated in recent studies [65-68], organic molecules have a crucial role in the formation of biosilica owing to the specificity of interactions at the organic-inorganic interface. Biosilicification has been studied most extensively in diatoms and sponges. The proteins involved in biosilicification in these different marine species will be reviewed here, along with the mechanistic basis for their function. 

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