title: Poly(silicate)-metabolizing silicatein in siliceous spicules and silicasomes of demosponges comprises dual enzymatic activities (silica polymerase and silica esterase).
abstract: Siliceous sponges can synthesize poly(silicate) for their spicules enzymatically using silicatein. We found that silicatein exists in silica-filled cell organelles (silicasomes) that transport the enzyme to the spicules. We show for the first time that recombinant silicatein acts as a silica polymerase and also as a silica esterase. The enzymatic polymerization/polycondensation of silicic acid follows a distinct course. In addition, we show that silicatein cleaves the ester-like bond in bis(p-aminophenoxy)-dimethylsilane. Enzymatic parameters for silica esterase activity are given. The reaction is completely blocked by sodium hexafluorosilicate and E-64. We consider that the dual function of silicatein (silica polymerase and silica esterase) will be useful for the rational synthesis of structured new silica biomaterials.
authors: Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität, Duesbergweg 6, Mainz, Germany. wmueller@uni-mainz.de
authors: Werner E G
authors: WE
authors: Müller
authors: Ute
authors: U
authors: Schlossmacher
authors: Xiaohong
authors: X
authors: Wang
authors: Alexandra
authors: A
authors: Boreiko
authors: David
authors: D
authors: Brandt
authors: Stephan E
authors: SE
authors: Wolf
authors: Wolfgang
authors: W
authors: Tremel
authors: Heinz C
authors: HC
authors: Schröder
mesh_terms: D000818:Animals; D002384:Catalysis; D002403:Cathepsins / Q000378:metabolism*; D004798:Enzymes / Q000378:metabolism*; D008855:Microscopy, Electron, Scanning; D015388:Organelles / Q000201:enzymology / Q000378:metabolism; D011161:Porifera / Q000201:enzymology / Q000378:metabolism*; D017640:Silicates / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D004798:Enzymes; D017640:Silicates; C112571:silicatein alpha; D002403:Cathepsins