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Soluble proteins control growth of skeleton crystals in three coralline demosponges
Citation key Lange2001
Author Lange, R. and Bergbauer, M. and Szewzyk, U. and Reitner, J.
Pages 195–201
Year 2001
DOI 10.1007/BF02668112
Journal Facies
Volume 45
Number 1
Abstract Calcified demosponges (coralline sponges, sclerosponges), the first metazoa producing a carbonate skeleton, used to be important reef building organisms in the past. The relatives of this group investigated here, Spirastrella (Acanthochaetetes) wellsi, Astrosclera willeyana and Vaceletia cf. crypta, are restricted to cryptic niches of modem Pacific coral reefs and may be considered as ,,living fossils". They are characterized by a basic biologically controlled metazoan biomineralization process. Each of the investigated taxa forms its calcareous basal skeleton in a highly specialized way. Moreover, each taxon secretes distinct Ca2+-binding macromolecules which were entrapped within the calcium carbonate crystals during skeleton formation. Therefore these Ca2(+)-binding macromolecules were also described as intracrystalline macromolecules. When isolated and separated by SDS polyacrylamide gel electrophoresis, the organic skeleton matrix of the three species revealed to be composed of a respective distinct array of EDTA-soluble proteins. A single protein of 41 kDa was detected in S. wellsi, two proteins of 38 and 120 kDa in A. willeyana, and four proteins of 18 kDa, 30 kDa, 33 kDa, and 37 kDa in Vaceletia sp. When run on IEF gel, the Ca2+-binding proteins gave staining bands at pH values between 5.25 and 5.65. As proved by an in vitro mineralization assay, the extracted proteins effectively inhibit CaCO3 and SrCO3 precipitation, respectively, in a saturated solution. Biochemical properties and behavior of the extracted proteins strongly suggest that they are involved in crystal nucleation and skeleton carbonate formation within the calcified sponges studied here.
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