Progressive accretion of amelogenin molecules during nanospheres assembly revealed by atomic force microscopy

Amelogenin proteins, the principal components of the developing dental enamel matrix, self-assemble to form nanosphere structures that are believed to function as structural components directly involved in the matrix mediated enamel biomineralization. The self-assembly behavior of a recombinant murine amelogenin (rM179) was investigated by atomic force microscopy (AFM) for further understanding the roles of amelogenin proteins in dental enamel biomineralization. Recombinant rM179 amelogenin was dissolved in a pH 7.4 Tris-HCl buffer at concentrations ranging from 12.5 to 300 microg/ml. The solutions were adsorbed on mica, fixed with Karnovsky fixative and rinsed thoroughly with water for atomic force microscopy (AFM). At low concentrations (12.5-50 microg/ml), nanospheres with diameters varying from 7 to 53 nm were identified while at concentrations ranging between 100-300 microg/ml the size distribution was significantly narrowed to be steadily between 10 and 25 nm in diameter. These nanospheres were observed to be the basic building blocks of both engineered rM179 gels and of the developing enamel extracellular matrix. The stable 15-20-nm nanosphere structures generated in the presence of high concentrations of amelogenins were postulated to be of great importance in facilitating the highly organized ultrastructural microenvironment required for the formation of initial enamel apatite crystallites.