Binding of Dentin Noncollagenous Matrix Proteins to Biological Mineral Crystals: An Atomic Force Microscopy Study

Abstract

Noncollagenous matrix proteins (NCPs) of dental hard tissues (dentin, cementum) are involved, both temporally and spatially, in the mineralization of their collagen matrices. Two of the NCPs thought to initiate mineral nucleation and control crystal growth in dentin, are dentin phosphoproteins (DPP) and dentin sialoprotein (DSP). Control of crystal growth would depend on the binding capacity of these two molecules, which may be related to the charge domains on the crystals and/or the phosphorylation of the protein. Phosphophoryn (a highly phosphorylated DPP) and DSP were isolated, purified, and characterized from the immature root apicies of human teeth. Dephosphorylation of phosphophoryn was carried out using bovine intestinal alkaline phosphatase. Enamel crystals were prepared from the maturation stage of developing rat incisor enamel. Protein-coated crystals were prepared for viewing in an atomic force microscope fluid cell using tapping mode. Desorption of the proteins was achieved using a phosphate buffer and surface roughness measurements were obtained from all specimens. Time-lapsed images of the crystals showed "nanospheres" of protein distributed along the crystals but only the phosphophoryn-coated crystals showed a distinctive banding pattern, which was still visible after the phosphate desorption experiments. The surface roughness measurements were statistically greater (P <0.01) when compared to the control for only the phosphophoryn-coated specimens. It is hypothesized that the phosphophoryn binding may be associated with charge arrays on the crystal surface and its phosphorylation. Also, based on its affinity for the crystalsurfaces, phosphophoryn seems the most likely candidate for controlling dentin crystal growth and morphology.

Amelogenesis Imperfecta and Other Biomineralization Defects in Fam20a and Fam20c Null Mice

“…matrix-specific precipitation of calcium phosphate on its own but relies on several different noncollagenous proteins that control nucleation and initial progression of mineralization. 31,32,45,107 In contrast, enamel mineralization takes place within a noncollagenous protein matrix that is secreted by ameloblasts of epithelial origin. This enamel matrix consists of specialized proteins that regulate the structural development and mineralization of enamel.…”

Dentine Remineralisation by Simulated Saliva Formulations with Different Ca and P_i Contents

“…Dentin remineralisation has been shown to be influenced by the presence of phosphoproteins, since they have the ability to bind Ca [Lee et al, 1977;Zanetti et al, 1981]. Therefore, they may act as template for remineralisation when immobilised or tightly bound in the collagen matrix [Lussi et al, 1988;Hunter et al, 1996;Wallwork et al, 2002], or inhibit remineralisation when present in relatively higher concentrations and free in solution [Clarkson et al, 1991[Clarkson et al, , 1998]. Since demineralisation by organic acids, such as the citric acid used in this study, has not shown the ability to remove loosely bound phosphoproteins [Clarkson et al, 1998], it can be suggested that remineralisation can happen even in the presence of these proteins, when at levels of P i as high as in solution E. However, this has yet to be further verified.…”

Mechanism of Mineralization of Collagen‐Based Connective Tissues

“…The dsppnull mice have decreased mineral contents in both their dentin [109] and their long bones (unpublished data). The mild decrease in bone mineralization is a surprising finding as there are very low levels of DSP in bone and almost undetectable levels of DPP although the dspp gene is expressed by osteoblasts [110].…”