title: Adsorption and interactions of dentine phosphoprotein with hydroxyapatite and collagen.
abstract: Dentine phosphoprotein (DPP) has been proposed to both promote and inhibit mineral deposition during dentinogenesis. The present study aimed to investigate the molecular interactions of DPP and dephosphorylated DPP (DPP-p) with hydroxyapatite (HAP). Bovine DPP was purified and dephosphorylated by alkaline phosphatase to obtain DPP-p. DPP and DPP-p adsorption to HAP was determined along with their ability, when free in solution or bound to collagen, to influence HAP-induced crystal growth. Absorption isotherms suggested that lower DPP concentrations (1.5-6.25 microg ml(-1)) demonstrated a reduced affinity for HAP compared with higher protein concentrations (12.5-50.0 microg ml(-1)). Dephosphorylated DPP had a much reduced affinity for HAP compared with DPP. Dentine phosphoprotein inhibited seeded HAP crystal growth, in a dose-dependent manner, whilst removal of the phosphate groups reduced this inhibition. When bound to collagen fibrils, DPP significantly promoted the rate of HAP crystal growth over 0-8 min. Conversely, DPP-p and collagen significantly decreased the rate of crystal growth over 0-18 min. These results indicate a major role for the phosphate groups present on DPP in HAP crystal growth. In addition, concentration-dependent conformational changes to DPP, and the interaction with other matrix components, such as collagen, are important in predicting its dual role in the mineralization of dentine.
authors.affiliation: Department of Clinical Dental Sciences, The University of Liverpool, Liverpool, UK.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Milan
authors.forename: Rachael V
authors.initials: RV
authors.lastname: Sugars
authors.forename: Graham
authors.initials: G
authors.lastname: Embery
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Waddington
mesh_terms: D000042:Absorption; D000327:Adsorption; D000469:Alkaline Phosphatase / Q000737:chemistry; D000818:Animals; D002417:Cattle; D003094:Collagen / Q000737:chemistry*; D003460:Crystallization; D017886:Durapatite / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry; D010750:Phosphoproteins / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D013696:Temperature; D013997:Time Factors
chemical_list: D010710:Phosphates; D010750:Phosphoproteins; C017630:phosphophoryn; D003094:Collagen; D017886:Durapatite; D000469:Alkaline Phosphatase