title: Regulation of calcium phosphate formation by native amelogenins in vitro.
abstract: Our previous in vitro studies have shown that recombinant full-length porcine amelogenin rP172 can transiently stabilize amorphous calcium phosphate (ACP) and uniquely guide the formation of well-aligned bundles of hydroxyapatite (HA) crystals, as seen in the secretory stage of amelogenesis. This functional capacity is dependent on the hydrophilic C-terminal domain of full-length amelogenin. However, we have also found that native phosphorylated (single S-16 site) forms of full-length (P173) and C-terminal cleaved (P148) amelogenins can stabilize ACP for > 2 d and prevent HA formation. The present study was carried out to test the hypothesis that, at reduced concentrations, native full-length P173 also has the capacity to guide ordered HA formation. The effect of P148 and P173 concentrations (0.2-2.0 mg/ml) on the rate of spontaneous calcium phosphate precipitation was monitored via changes in solution pH, while mineral phases formed were assessed using TEM. At higher P173 concentrations (1.0-2.0 mg/ml), limited mineral formation occurred and only ACP nanoparticles were observed during a 48 h period. However, at 0.4 mg/ml P173, a predominance of organized bundles of linear, needle-like HA crystals were observed. At 0.2 mg/ml of P173, limited quantities of less organized HA crystals were found. Although P148 similarly stabilized ACP, it did not guide ordered HA formation, like P173. Hence, the establishment of the hierarchical enamel structure during secretory stage amelogenesis may be regulated by the partial removal of full-length amelogenin via MMP20 proteolysis, while predominant amelogenin degradation products, like P148, serve to prevent uncontrolled mineral formation.
authors.affiliation: Department of Applied Oral Sciences, Center for Biomineralization, The Forsyth Institute , Cambridge, MA , USA .
authors.forename: Seo-Young
authors.initials: SY
authors.lastname: Kwak
authors.forename: Sonia
authors.initials: S
authors.lastname: Kim
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Yamakoshi
authors.forename: James P
authors.initials: JP
authors.lastname: Simmer
authors.forename: Elia
authors.initials: E
authors.lastname: Beniash
authors.forename: Henry C
authors.initials: HC
authors.lastname: Margolis
mesh_terms: D053523:Amelogenin / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002130:Calcium Phosphates / Q000378:metabolism*; D017886:Durapatite / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D010766:Phosphorylation; D059748:Proteolysis; D013552:Swine
chemical_list: D053523:Amelogenin; D002130:Calcium Phosphates; D017886:Durapatite; C020243:calcium phosphate
keywords: Amorphous calcium phosphate; enamel; enamel matrix protein; hydroxyapatite; kinetics; mineralization