title: Effect of phosphorylation on the interaction of calcium with leucine-rich amelogenin peptide.
abstract: Amelogenin undergoes self-assembly and plays an essential role in guiding enamel mineral formation. The leucine-rich amelogenin peptide (LRAP) is an alternative splice product of the amelogenin gene and is composed of the N terminus (containing the only phosphate group) and the C terminus of full-length amelogenin. This study was conducted to investigate further the role of phosphorylation in LRAP self-assembly in the presence and absence of calcium using small angle X-ray scattering (SAXS). Consistent with our previous dynamic light-scattering findings for phosphorylated (+P) and non-phosphorylated (-P) LRAP, SAXS analyses revealed radii of gyration (R(g)) for LRAP(-P) (46.3-48.0 Å) that were larger than those for LRAP(+P) (25.0-27.4 Å) at pH 7.4. However, added calcium (up to 2.5 mM) induced significant increases in the R(g) of LRAP(+P) (up to 46.4 Å), while it had relatively little effect on LRAP(-P) particle size. Furthermore, SAXS analyses suggested compact folded structures for LRAP(-P) in the presence and absence of calcium, whereas the conformation of LRAP(+P) changed from an unfolded structure to a more compact structure upon the addition of calcium. We conclude that the single phosphate group in LRAP(+P) induces functionally important conformational changes, suggesting that phosphorylation may also influence amelogenin conformation and protein-mineral interactions during the early stages of amelogenesis.
authors.affiliation: Department of Biomineralization, The Forsyth Institute, Cambridge, MA 02142, USA.
authors.forename: Elvire
authors.initials: E
authors.lastname: Le Norcy
authors.forename: Seo-Young
authors.initials: SY
authors.lastname: Kwak
authors.forename: Marc
authors.initials: M
authors.lastname: Allaire
authors.forename: Peter
authors.initials: P
authors.lastname: Fratzl
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Yamakoshi
authors.forename: James P
authors.initials: JP
authors.lastname: Simmer
authors.forename: Henry C
authors.initials: HC
authors.lastname: Margolis
mesh_terms: D053523:Amelogenin / Q000737:chemistry*; D000595:Amino Acid Sequence; D000818:Animals; D002113:Calcification, Physiologic; D002118:Calcium / Q000737:chemistry*; D003746:Dental Enamel Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D053758:Nanoparticles; D010316:Particle Size; D010766:Phosphorylation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle; D034421:Sus scrofa; D014961:X-Ray Diffraction
chemical_list: D053523:Amelogenin; D003746:Dental Enamel Proteins; C067432:leucine-rich amelogenin peptide; D002118:Calcium