Molecular Insights into Making Tooth Enamel
The aim of this study in the journal Archives of Oral Biology was to identify the major proteolytic products generated by a protein known as matrix metalloproteinase-20 (MMP20). The primary function of MMP20 is to remove a protein, amelogenin, that is responsible for the generation of tooth enamel in a process called amelogenesis. Amelogenin is the dominant protein in amelogenesis, but, at the end of the process it is gone. Failure to remove amelogenin results in enamel that is discolored and brittle, hence, its “destruction” by MMP20 into smaller pieces that can be removed is essential for proper enamel formation.
Researchers used a novel combination of high-performance liquid chromatography and nuclear magnetic resonance (NMR) spectroscopy to identify the major products of MMP20 cleavage of amelogenin. They also wanted to unambiguously determine if the tyrosine-rich amelogenin peptide (TRAP) was a substrate of MMP20. This is because TRAP was previously thought to be an end-product of MMP20 proteolysis of amelogenin and degraded by other proteases.
The study provides an improved understanding of how MMP20 modifies amelogenin in preparation for its removal. This understanding may provide new insights into the molecular basis for enamel formation, which in turn may lead to new repair or regeneration strategies for tooth enamel.
Tooth enamel is one of the hardest tissues in nature. It needs to be tough because it must withstand a lifetime of abuse within the bacteria-filled confines of the mouth.
Amelogenin is the predominant matrix protein found in ameloblasts cells in the first stage of tooth development. By the end of the tooth maturation process, amelogenin is gone, having been digested primarily by the enzyme MMP20, leaving enamel largely devoid of protein (making it the most mineralized tissue in vertabrates).
While many MMP20 cleavage products of amelogenin have previously been identified by SDS-PAGE and a combination of reverse-phase chromatography and mass spectrometry, there was a paucity of information on the relative quantities of the major cleavage products over time. In this study, researchers used NMR spectroscopy to focus on only the major proteolysis products. Among their findings was the observation that TRAP, a major product of the MMP20 digestion of amelogenin, can be further processed by MMP20 into smaller proteolytic fragments. These results provide a better understanding of the enamel formation process that could lead to new repair or regeneration strategies for tooth enamel.
G.W. Buchko, R. Jayasinha Arachchige, J. Tao, B.J. Tarasevich, W.J. Shaw “Identification of major matrix metalloproteinase-20 proteolytic processing products of murine amelogenin and tyrosine-rich amelogenin peptide using a nuclear magnetic resonance spectroscopy based method.” Arch. Oral Biology, 93:187-194, (2018). [doi.org/10.1016/j.archoralbio.2018.06.001]