title: Primary structure and post-translational modifications of silicatein beta from the marine sponge Petrosia ficiformis (Poiret, 1789).
abstract: Biosilica is an amazing example of natural order and complexity. Siliceous sponge spicules, in particular, are characterized by a large variety of dimensions and shapes, with an ultrastructure based on silica nanoparticles strictly packaged around an axial filament constituted by a family of proteins called silicateins. These peculiar proteins have a high sequence homology with cathepsins and they play a double role of enzyme and template in the control of biosilica precipitation. However, their natural structural organization inside the spicules is far from being understood in details. In this work, axial filaments extracted from spicules of Petrosia ficiformis have been extensively analyzed by mass spectrometry, exploiting MALDI and ESI analysis of both the intact protein and the peptides coming from digestion of the axial filament with different proteases. Results demonstrate that P. ficiformis spicules contain almost only silicatein beta. Several post-translational modifications, like methylations at the N-terminal region, three phosphorylation sites, and the oxidation of a histidine and of a cysteine to cysteic acid, are described.
authors.affiliation: Centro Biotecnologie Avanzate, Genova, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Armirotti
authors.forename: Gianluca
authors.initials: G
authors.lastname: Damonte
authors.forename: Marina
authors.initials: M
authors.lastname: Pozzolini
authors.forename: Francesca
authors.initials: F
authors.lastname: Mussino
authors.forename: Carlo
authors.initials: C
authors.lastname: Cerrano
authors.forename: Annalisa
authors.initials: A
authors.lastname: Salis
authors.forename: Umberto
authors.initials: U
authors.lastname: Benatti
authors.forename: Marco
authors.initials: M
authors.lastname: Giovine
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002403:Cathepsins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D030562:Databases, Protein; D008969:Molecular Sequence Data; D047130:Petrosia / Q000201:enzymology* / Q000648:ultrastructure; D011499:Protein Processing, Post-Translational; D016415:Sequence Alignment; D012821:Silanes / Q000737:chemistry / Q000378:metabolism; D012822:Silicon Dioxide / Q000378:metabolism; D012995:Solubility; D053719:Tandem Mass Spectrometry
chemical_list: D012821:Silanes; C040733:tetraethoxysilane; D012822:Silicon Dioxide; D002403:Cathepsins