PROTEIN INTERACTIONS DURING ASSEMBLY OF THE ENAMEL ORGANIC EXTRACELLULAR-MATRIX

Enamel is the outermost covering of teeth and contains the largest hyd roxyapatite crystallites formed in the vertebrate body. Enamel forms e xtracellularly through the ordered assembly of a protein scaffolding t hat regulates crystallite dimensions. The two most studied proteins of the enamel extracellular matrix (ECM) are amelogenin and tuftelin. Th e underlying mechanism for assembly of the proteins within the enamel extracellular matrix and the regulatory role of crystallite-protein in teractions have proven elusive. We used the two-hybrid system to ident ify and define minimal protein domains responsible for supra molecular assembly of the enamel ECM, We show that amelogenin proteins self-ass emble, and this self-assembly depends on the amino-terminal 42 residue s interacting either directly or indirectly with a 17-residue domain i n the carboxyl region, Amelogenin and tuftelin fail to interact with e ach other. Based upon this data, and advances in the field, a model fo r amelogenin assemblies that direct enamel biomineralization is presen ted.