Structural characterization of siliceous spicules from marine sponges.
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.
Croce
Gianluca
G
Dipartimento di Scienze e Tecnologie Avanzate, Università del Piemonte Orientale A. Avogadro, I-15100 Alessandria, Italy.
Frache
Alberto
A
Milanesio
Marco
M
Marchese
Leonardo
L
Causà
Mauro
M
Viterbo
Davide
D
Barbaglia
Alessia
A
Bolis
Vera
V
Bavestrello
Giorgio
G
Cerrano
Carlo
C
Benatti
Umberto
U
Pozzolini
Marina
M
Giovine
Marco
M
Amenitsch
Heinz
H
D000818:Animals; D002403:Cathepsins / Q000032:analysis / Q000737:chemistry* / Q000648:ultrastructure*; D016326:Extracellular Matrix Proteins / Q000032:analysis / Q000737:chemistry / Q000648:ultrastructure; D008386:Marine Biology / Q000379:methods; D008958:Models, Molecular; D011161:Porifera / Q000737:chemistry* / Q000145:classification / Q000648:ultrastructure*; D011487:Protein Conformation; D012822:Silicon Dioxide / Q000032:analysis / Q000737:chemistry*; D013045:Species Specificity
D016326:Extracellular Matrix Proteins; C112571:silicatein alpha; D012822:Silicon Dioxide; D002403:Cathepsins