title: Fiber diffraction study of spicules from marine sponges.
abstract: A synchrotron radiation fiber diffraction structural study of the axial filament of siliceous spicules from two species of marine sponges (the Demosponge Geodia cydonium and the Hexactinellid Scolymastra joubini) was carried out. The sharpness of the spots in the diffraction patterns indicated that the protein units in the filament of both samples were highly organized. A possible explanation is that the arrangement of the protein units is similar to that of the pores in highly ordered siliceous mesoporous materials. Nevertheless, the diffraction patterns are quite different for the two types of spicules. The pattern of G. cydonium is consistent with a regular 2D hexagonal lattice of protein units in the direction perpendicular to the spicule axis, with a repeating distance of 5.8 nm; the units are linked to form fibers along the axis. The pattern of S. joubini indicates the presence of two different 2D lattices in which the repeating protein units are inclined by +50 degrees and -50 degrees with respect to the elongation axis; the distance between the units increases to 8.4 nm. This 2D model is consistent with hexagonal packing of spirally oriented cylindrical protein units elongated along the filament axis.
authors.affiliation: DISTA, Universita' del Piemonte Orientale A. Avogadro, I-15100 Alessandria, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Croce
authors.forename: Alberto
authors.initials: A
authors.lastname: Frache
authors.forename: Marco
authors.initials: M
authors.lastname: Milanesio
authors.forename: Davide
authors.initials: D
authors.lastname: Viterbo
authors.forename: Giorgio
authors.initials: G
authors.lastname: Bavestrello
authors.forename: Umberto
authors.initials: U
authors.lastname: Benatti
authors.forename: Marco
authors.initials: M
authors.lastname: Giovine
authors.forename: Heinz
authors.initials: H
authors.lastname: Amenitsch
mesh_terms: D000818:Animals; D011161:Porifera / Q000502:physiology* / Q000648:ultrastructure*; D011487:Protein Conformation; D012822:Silicon Dioxide / Q000737:chemistry* / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D012822:Silicon Dioxide