Limited proteolysis of amelogenin: toward understanding the proteolytic processes in enamel extracellular matrix

This article is a short review of our recent study on controlled proteolysis of amelogenins by a series of commercially available proteinases as well as the tooth-specific metalloproteinase enamelysin. A limited proteolysis approach and mass spectrometry were applied in order to determine the surface accessibility of conserved domains of amelogenin nanospheres. Furthermore, this study was aimed at exploring the factors that affect the activity of enamel proteases to process amelogenins and at providing insight into the mechanisms of amelogenin degradation during amelogenesis. We found that, under limited conditions, certain amino acid residues at both the C- and N-termini of amelogenin are accessible to proteolytic action by a series of proteinases, suggesting that these regions are exposed on the surface of amelogenin nanospheres. Recombinant enamelysin cleaved amelogenin at the C-terminal region, showing a preference of the enzyme to cleave the S/M and F/S bonds. This result of enamelysin activity on amelogenin explains the abundance of the p148 (20k) pig amelogenin during the secretory stage of amelogenesis.