Structural Characterization of Siliceous Spicules from Marine Sponges |
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Authors: | Gianluca Croce Marco Milanesio Mauro Causà Alessia Barbaglia Giorgio Bavestrello Umberto Benatti Marco Giovine |
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Institution: | * Dipartimento di Scienze e Tecnologie Avanzate, Università del Piemonte Orientale “A. Avogadro”, I-15100 Alessandria, Italy † Dipartimento di Scienze Chimiche Alimentari Farmaceutiche e Farmacologiche, Università del Piemonte Orientale “A. Avogadro”, I-28100 Novara, Italy ‡ Dipartimento di Scienze del Mare, Università Politecnica delle Marche, I-60100 Ancona, Italy § Dipartmento per lo Studio del Territorio e sue Risorse, Università di Genova, 16132 Genova, Italy ¶ Dipartmento di Medicina Sperimentale sezione Biochimica, Università di Genova, I-16132 Genova, Italy || Centro Nazionale delle Ricerche, Direzione Progetto Finalizzato Biotecnologie, I-16132 Genova, Italy ** Institute of Biophysics and X-Ray Structure Research, Austrian Academy of Sciences, A-8042 Graz, Austria |
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Abstract: | Siliceous sponges, one of the few animal groups involved in a biosilicification process, deposit hydrated silica in discrete skeletal elements called spicules. A multidisciplinary analysis of the structural features of the protein axial filaments inside the spicules of a number of marine sponges, belonging to two different classes (Demospongiae and Hexactinellida), is presented, together with a preliminary analysis of the biosilicification process. The study was carried out by a unique combination of techniques: fiber diffraction using synchrotron radiation, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetric (DSC), Fourier transform infrared spectroscopy (FTIR), and molecular modeling. From a phylogenetic point of view, the main result is the structural difference between the dimension and packing of the protein units in the spicule filaments of the Demospongiae and the Hexactinellida species. Models of the protein organization in the spicule axial filaments, consistent with the various experimental evidences, are given. The three different species of demosponges analyzed have similar general structural features, but they differ in the degree of order. The structural information on the spicule axial filaments can help shed some light on the still unknown molecular mechanisms controlling biosilicification. |
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