title: An oligomeric C-RING nacre protein influences prenucleation events and organizes mineral nanoparticles.
abstract: The mollusk shell nacre layer integrates mineral phases with macromolecular components such as intracrystalline proteins. However, the roles performed by intracrystalline proteins in calcium carbonate nucleation and subsequent postnucleation events (e.g., organization of mineral deposits) in the nacre layer are not known. We find that AP7, a nacre intracrystalline C-RING protein, self-assembles to form amorphous protein oligomers and films on mica that further assemble into larger aggregates or phases in the presence of Ca2+. Using solution nuclear magnetic resonance spectroscopy, we determine that the protein assemblies are stabilized by interdomain interactions involving the aggregation-prone T31-N66 C-terminal C-RING domain but are destabilized by the labile nature of the intrinsically disordered D1-T19 AA N-terminal sequence. Thus, the dynamic, amorphous nature of the AP7 assemblies can be traced to the molecular behavior of the N-terminal sequence. Using potentiometric methods, we observe that AP7 protein phases prolong the time interval for prenucleation cluster formation but neither stabilize nor destabilize ACC clusters. Time-resolved flow cell scanning transmission electron microscopy mineralization studies confirm that AP7 protein phases delay the onset of nucleation and assemble and organize mineral nanoparticles into ring-shaped branching clusters in solution. These phenomena are not observed in protein-deficient assays. We conclude that C-RING AP7 protein phases modulate the time period for early events in nucleation and form strategic associations with forming mineral nanoparticles that lead to mineral organization.
authors.affiliation: Laboratory for Chemical Physics, Division of Basic Sciences, and Center for Skeletal Biology, New York University , 345 East 24th Street, New York, New York 10010, United States.
authors.forename: Iva
authors.initials: I
authors.lastname: Perovic
authors.forename: Andreas
authors.initials: A
authors.lastname: Verch
authors.forename: Eric P
authors.initials: EP
authors.lastname: Chang
authors.forename: Ashit
authors.initials: A
authors.lastname: Rao
authors.forename: Helmut
authors.initials: H
authors.lastname: Cölfen
authors.forename: Roland
authors.initials: R
authors.lastname: Kröger
authors.forename: John Spencer
authors.initials: JS
authors.lastname: Evans
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D049851:Gastropoda / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D060734:Nacre / Q000737:chemistry / Q000378:metabolism*; D053758:Nanoparticles / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D011486:Protein C; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D060734:Nacre; D011486:Protein C; D011506:Proteins; D011994:Recombinant Proteins; D002118:Calcium