Protein self-assembly creates a nanoscale device for biomineralization

Mammalian enamel is the unique hierarchically organized bioceramic material that owes its existence to a transient precursor, the enamel organic extracellular matrix. The organic matrix is biosynthesized by epithelial derived cells called ameloblasts and the selection of genes expressed, the timing and amount of proteins expressed serve to impose constraints on the matrix. The protein matrix components undergo self-assembly to form a microenvironment that regulates the mineral phase, serving to control crystal habit and spacing between crystallites. We have focused on amelogenin, the most abundant protein of the enamel organic matrix. Amelogenin self-assembles into nanospheres that participate in control over enamel organization. Ameloblasts also interact with the matrix and these interactions are important to the organization of hydroxyapatite crystallites into woven bundles. Changes to conserved domains within amelogenin alter protein-to-protein interactions as well as cell to matrix interactions. Changes to enamel organization observed during evolution may be accounted for, in part, by changes to critical domains within enamel proteins that form the matrix.