Enamelysin (Matrix Metalloproteinase-20): Localization in the Developing Tooth and Effects of pH and Calcium on Amelogenin Hydrolysis

Abstract

The formation of dental enamel is a precisely regulated and dynamic developmental process. The forming enamel starts as a soft, protein-rich tissue and ends as a hard tissue that is over 95% mineral by weight. Intact amelogenin and its proteolytic cleavage products are the most abundant proteins present within the developing enamel. Proteinases are also present within the enamel matrix and are thought to help regulate enamel development and to expedite the removal of proteins prior to enamel maturation. Recently, a novel matrix metalloproteinase named enamelysin was cloned from the porcine enamel organ. Enamelysin transcripts have previously been observed in the enamel organ and dental papillae of the developing tooth. Here, we show that the sources of the enamelysin transcripts are the ameloblasts of the enamel organ and the odontoblasts of the dental papilla. Furthermore, we show that enamelysin is present within the forming enamel and that it is transported in secretory vesicles prior to its secretion from the ameloblasts. We also characterize the ability of recombinant enamelysin (rMMP-20) to degrade amelogenin under conditions of various pHs and calcium ion concentrations. Enamelysin displayed the greatest activity at neutral pH (7.2) and high calcium ion concentration (10 mM). During the initial stages of enamel formation, the enamel matrix maintains a neutral pH of between 7.0 and 7.4. Thus, enamelysin may play a role in enamel and dentin formation by cleaving proteins that are also present during these initial developmental stages.

Internalization of amelogenin by dendritic cells of the papillary layer during transition and early maturation stages

“…Although the molecular sizes of degraded enamel proteins for resorption are so far unclear, several proteinases have been found in enamel (Tanabe et al 1992;Fukae et al 1998;. Therefore, the present results and those of previous reports (Nanci et al 1987 in which anti-amelogenin positive materials were detected in intercellular spaces of the papillary and ameloblast layers are reasonable, and may show that degraded enamel proteins are transported from enamel surface to the intercellular spaces.…”

Enamelysin (Matrix Metalloproteinase 20)-deficient Mice Display an Amelogenesis Imperfecta Phenotype

“…Previously, several studies show that recombinant enamelysin cleaves recombinant amelogenin (21,24,26,44), including a study demonstrating that recombinant amelogenin was cleaved at virtually all of the precise cleavage sites that had previously been observed in vivo (28). However, until now (Fig.…”

MMP20 Hemopexin Domain Mutation in Amelogenesis Imperfecta

“…The only post-translational modification is a disulfide bridge connecting the first and last amino acids of the hemopexin domain (Yamada et al, 2003). In the pig, active MMP20 migrates as a doublet at 46 and 41 kDa on casein zymograms (Fukae et al, 1998). Both bands are comprised of the catalytic, linker, and hemopexin domains, but two bands are observed because "nicking' (cleavage that does not release a peptide because of the disulfide bridge connection) of the hemopexin domain causes a change in its mobility on SDS-PAGE.…”