title: A Model Sea Urchin Spicule Matrix Protein Self-Associates To Form Mineral-Modifying Protein Hydrogels.
abstract: In the purple sea urchin Strongylocentrotus purpuratus, the formation and mineralization of fracture-resistant skeletal elements such as the embryonic spicule require the combinatorial participation of numerous spicule matrix proteins such as the SpSM30A-F isoforms. However, because of limited abundance, it has been difficult to pursue extensive biochemical studies of the SpSM30 proteins and deduce their role in spicule formation and mineralization. To circumvent these problems, we expressed a model recombinant spicule matrix protein, rSpSM30B/C, which possesses the key sequence attributes of isoforms "B" and "C". Our findings indicate that rSpSM30B/C is expressed in insect cells as a single polypeptide containing variations in glycosylation that create microheterogeneity in rSpSM30B/C molecular masses. These post-translational modifications incorporate O- and N-glycans and anionic mono- and bisialylated and mono- and bisulfated monosaccharides on the protein molecules and enhance its aggregation propensity. Bioinformatics and biophysical experiments confirm that rSpSM30B/C is an intrinsically disordered, aggregation-prone protein that forms porous protein hydrogels that control the in vitro mineralization process in three ways: (1) increase the time interval for prenucleation cluster formation and transiently stabilize an ACC polymorph, (2) promote and organize single-crystal calcite nanoparticles, and (3) promote faceted growth and create surface texturing of calcite crystals. These features are also common to mollusk shell nacre proteins, and we conclude that rSpSM30B/C is a spiculogenesis protein that exhibits traits found in other calcium carbonate mineral modification proteins.
authors.affiliation: Laboratory for Chemical Physics, Center for Skeletal and Craniofacial Biology, New York University , 345 East 24th Street, New York, New York 10010, United States.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Jain
authors.affiliation: Laboratory for Chemical Physics, Center for Skeletal and Craniofacial Biology, New York University , 345 East 24th Street, New York, New York 10010, United States.
authors.forename: Martin
authors.initials: M
authors.lastname: Pendola
authors.affiliation: Department of Chemistry, Physical Chemistry, Universität Konstanz , Universitätstrasse 10, D-78457 Konstanz, Germany.
authors.forename: Ashit
authors.initials: A
authors.lastname: Rao
authors.affiliation: Department of Chemistry, Physical Chemistry, Universität Konstanz , Universitätstrasse 10, D-78457 Konstanz, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Cölfen
authors.affiliation: Laboratory for Chemical Physics, Center for Skeletal and Craniofacial Biology, New York University , 345 East 24th Street, New York, New York 10010, United States.
authors.forename: John Spencer
authors.initials: JS
authors.lastname: Evans
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002119:Calcium Carbonate / Q000737:chemistry / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006031:Glycosylation; D020100:Hydrogels; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D008903:Minerals / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D047270:Strongylocentrotus purpuratus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D003598:Cytoskeletal Proteins; D020100:Hydrogels; D008903:Minerals; D020033:Protein Isoforms; D011994:Recombinant Proteins; C071119:SM30 protein, Strongylocentrotus purpuratus; D002119:Calcium Carbonate