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Issue 6, 2014
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The sponge silicatein-interacting protein silintaphin-2 blocks calcite formation of calcareous sponge spicules at the vaterite stage

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Abstract

Ca-carbonate, the inorganic matrix of the spicules from the calcareous sponges, is formed as the result of an enzyme-catalyzed reaction with the carbonic anhydrase [CA] as a decisive component. The growth and the morphology of the spicules are genetically controlled, and are taxon-specific. In the present study it is shown that the silicatein-interacting protein silintaphin-2 is present at the surface of the siliceous spicules of the demosponge Suberites domuncula and prevents the association of calcareous crystals synthesized in vitro to these skeletal elements. Silintaphin-2 comprises a Ca2+-binding domain that is formed by a 22 amino acid-long peptide, N-DDDSQGEIQSDMAEEEDDDNVD-C. This very acidic 22-meric peptide, termed D/E-peptide, is shown to decelerate the in vitro synthesis of calcite through blocking the transformation of amorphous Ca-carbonate to the crystalline morph calcite at the level of vaterite. This effect is seen at a molar ratio of D/E-peptide : Ca2+ of 1 : 5000. During the deposition of Ca-carbonate the peptide becomes incorporated into the crystallites. Determinations of the mechanical characteristics of the formed Ca-carbonate deposits revealed a hardness of 1.98 ± 0.31 GPa (calcite) and 1.38 ± 0.39 GPa (vaterite), an elastic modulus of 72.83 ± 11.68 GPa (calcite) and 39.13 ± 8.04 GPa (vaterite) and a creep of 5.44 ± 1.15 (calcite) and 9.95 ± 1.60 (vaterite) per maximal depth (%). It is concluded that the D/E-peptide interferes with the Ca2+ ions within the growing vaterite crystals and freezes this unstable phase formed during calcite formation. It is postulated that proteins, like silintaphin-2 with its Ca2+-binding domain D/E-peptide, are involved in the taxon-specific control of the synthesis of the inorganic matrix of the sponge spicules.

Graphical abstract: The sponge silicatein-interacting protein silintaphin-2 blocks calcite formation of calcareous sponge spicules at the vaterite stage

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Publication details

The article was received on 17 Sep 2013, accepted on 05 Nov 2013 and first published on 20 Nov 2013


Article type: Paper
DOI: 10.1039/C3RA45193C
Citation: RSC Adv., 2014,4, 2577-2585
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    The sponge silicatein-interacting protein silintaphin-2 blocks calcite formation of calcareous sponge spicules at the vaterite stage

    W. E. G. Müller, M. Neufurth, U. Schlossmacher, H. C. Schröder, D. Pisignano and X. Wang, RSC Adv., 2014, 4, 2577
    DOI: 10.1039/C3RA45193C

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