Enzymatic processing of amelogenin during continuous crystallization of apatite


Dental enamel forms through a protein-controlled mineralization and enzymatic degradation process with a nanoscale precision that new engineering technologies may be able to mimic. Recombinant full-length human amelogenin (rH174) and a matrix-metalloprotease (MMP-20) were used in a pH-stat titration system that enabled a continuous supply of calcium and phosphate ions over several days, mimicking the initial stages of matrix processing and crystallization in enamel in vitro. Effects on the self-assembly and crystal growth from a saturated aqueous solution containing 0.4 mg/mL rH174 and MMP-20 with the weight ratio of 1:1000 with respect to rH174 were investigated. A transition from nanospheres to fibrous amelogenin assemblies was facilitated under conditions that involved interaction between rH174 and its proteolytic cleavage products. Despite continuous titration, the levels of calcium exhibited a consistent trend of decreasing, thereby indicating a possible role in protein self-assembly. This study suggests that mimicking enamel formation in vitro requires the synergy between the aspects of matrix self-assembly, proteolysis, and crystallization.

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The presented study was supported by NIH/NIDCR Grants R01-DE17529 and R01-DE015821. The authors acknowledge the assistance of Xiaodong He for providing the AFM images of the assembly of pure rH174 and rH163 suspensions and H. Ewa Witkowska, Sarah Robinson, Venu Varanasi, Markus Hardt, and Steve Hall for the MALDI-TOF analyses. The UCSF Biomolecular Resource Center Mass Spectrometry facility was supported by a grant from the Sandler New Technology Fund.

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Uskoković, V., Kim, MK., Li, W. et al. Enzymatic processing of amelogenin during continuous crystallization of apatite. Journal of Materials Research 23, 3184–3195 (2008). https://doi.org/10.1557/JMR.2008.0387

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