Silicateins are

enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

which catalyse the formation of biosilica from monomeric silicon compounds (such as silicic acid) extracted from the natural environment.Müller, W.E., Boreiko, A., Wang, X., Belikov, S.I., Wiens, M., Grebenjuk, V.A., Schloβmacher, U. and Schröder, H.C., 2007. Silicateins, the major biosilica forming enzymes present in demosponges: protein analysis and phylogenetic relationship. Gene, 395(1-2), pp.62-71. doi:10.1016/j.gene.2007.02.014 Environmental silicates are absorbed by specific biota, including

diatoms A diatom (New Latin, Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group com ...

, radiolaria,

silicoflagellate Dictyochales (Silicoflagellates, or Dictyochophyceae ''sensu stricto'') are a small group of unicellular heterokont algae, found in marine environments. Characteristics In one stage of their life cycle, they produce a siliceous skeleton, compo ...

s, and siliceous sponges; silicateins have so far only been found in

sponges Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through ...

. Silicateins are homologous to the

cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometime ...

protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...

cathepsin.Otzen D. (2012). The role of proteins in biosilicification. Scientifica, 2012, 867562. doi:10.6064/2012/867562 In sponges, the silicatein enzymes reside in the axial filaments of the axial canals of the siliceous

spicules Spicules are any of various small needle-like anatomical structures occurring in organisms Spicule may also refer to: *Spicule (sponge), small skeletal elements of sea sponges *Spicule (nematode), reproductive structures found in male nematodes ( ...

. In contrast,

do not use silicateins but rather small specialised peptides called silaffins which attach long chain

polyamine A polyamine is an organic compound having more than two amino groups. Alkyl polyamines occur naturally, but some are synthetic. Alkylpolyamines are colorless, hygroscopic, and water soluble. Near neutral pH, they exist as the ammonium derivatives. ...

s (LCPAs) to lysine groups. Free LCPAs can also cooperate with silaffins. Both silicateins and silaffins form higher-order structures which act both as structural templates (for exoskeletons) and mechanistic catalysts for the polycondensation reactions of silicon-compounds. The

Venus' flower basket The Venus' flower basket (''Euplectella aspergillum'') is a glass sponge in the phylum Porifera. It is a marine sponge found in the deep waters of the Pacific ocean, usually at depths below 500 meters. Like other sponges, they feed by filtering s ...

siliceous sponge is a well-known example of an organism that utilises silicatein. It is known for its remarkable ability to extract silicic acid from surrounding seawater, which is then converted into complex 3D

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

structures at ambient temperatures underwater, something human engineering capabilities are unable to replicate without the use of high-temperature. Another example of silicatein-utilising organisms are the suberites, a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of sea sponge in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Suberitidae Suberitidae is a family of sea sponges belonging to the order Suberitida. Genera *Suberites *Homaxinella *Rhizaxinella *Caulospongia *Pseudospongosorites *Aaptos ... References

Suberitidae, Sponge families {{demosponge-stub ...

. Suberites consist mostly of cells, in contrast with other ''

Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through th ...

'' (such as the class Hexactinellida, to which the

belongs) which are

syncytial A syncytium (; plural syncytia; from Greek: σύν ''syn'' "together" and κύτος ''kytos'' "box, i.e. cell") or symplasm is a multinucleate cell which can result from multiple cell fusions of uninuclear cells (i.e., cells with a single nucleus) ...

.W. Muller, Review: How was metazoan threshold crossed? The hypothetical Urmetazoa. Comparative Biochemistry and Physiology Part A 129, 433 (2001). doi:10.1016/s1095-6433(00)00360-3 The extracellular matrix of siliceous

give suberites their structural foundation; these consist of bio-silica, a silicon dioxide polymer.W. Xiaohong et al., Evagination of Cells Controls Bio-Silica Formation and Maturation during Spicule Formation in Sponges. PLoS ONE 6, 1 (2011). doi:10.1371/journal.pone.0020523 These inorganic structures provide support for the animals.X. Wang et al., Silicateins, silicatein interactors and cellular interplay in sponge skeletogenesis: formation of glass fiber-like spicules. FEBS Journal 279, 1721 (2012) https:/doi.org10.1111/j.1742-4658.2012.08533.x Silica deposition begins intracellularly and is carried out by the enzyme silicatein. Silicateins are modulated by a group of proteins called silintaphins The process occurs in specialized cells known as sclerocytes.

Lubomirskia baikalensis ''Lubomirskia baikalensis'' is a freshwater species of sponge that is endemic to Lake Baikal, Russia. It is commonly called the Lake Baikal sponge and it is the most abundant sponge in the lake, but all the approximately 15 species of sponges in ...

, also known as

Lake Baikal Lake Baikal (, russian: Oзеро Байкал, Ozero Baykal ); mn, Байгал нуур, Baigal nuur) is a rift lake in Russia. It is situated in southern Siberia, between the federal subjects of Irkutsk Oblast to the northwest and the Repu ...

sponge, has been studied to explore the gene family of silicateins and their role in the morphogenesis of these sponges.Belikov; Kaluzhnaya; Schröder; Müller; and Müller (2007)
Lake Baikal endemic sponge Lubomirskia baikalensis: structure and organization of the gene family of silicatein and its role in morphogenesis
Porifera Research: Biodiversity, Innovation and Sustainability, pp. 179-188

References

{{CC-notice, cc=by3, url=https://www.hindawi.com/journals/scientifica/2012/867562/, author(s)=Otzen, Daniel Protein families Sponge biology