MMP20 Proteolysis of Native Amelogenin Regulates Mineralization In Vitro.

Area of Science:

• Biomineralization
• Dental Enamel Formation
• Protein Chemistry

Background:

• Native phosphorylated full-length porcine amelogenin (P173) and its cleavage product (P148) inhibit spontaneous calcium phosphate formation in vitro.
• P173 is proteolyzed by matrix metalloproteinase 20 (MMP20) shortly after secretion.
• The role of amelogenin proteolysis in regulating calcium phosphate formation remains to be fully elucidated.

Purpose of the Study:

• To assess the effect of amelogenin proteolysis by MMP20 on calcium phosphate formation.
• To investigate the distinct roles of P173 and P148 in mineral phase stabilization and crystal formation.

Main Methods:

• Sequential addition of calcium and phosphate to protein solutions with and without MMP20 under physiological conditions.
• Assessment of protein degradation using gel electrophoresis.
• Characterization of mineral products using transmission electron microscopy (TEM).

Main Results:

• MMP20 cleaved P173 primarily into P148, but did not cleave P148.
• P173 with MMP20 promoted the formation of well-aligned hydroxyapatite (HA) crystals.
• In the absence of MMP20, only amorphous calcium phosphate (ACP) particles were observed.
• P148 stabilized ACP and prevented HA formation, especially when proteolysis was absent.

Conclusions:

• Proteolysis of full-length amelogenin by MMP20 regulates the transformation of ACP to ordered enamel crystals.
• The predominant amelogenin degradation product, P148, primarily prevents uncontrolled mineral formation during enamel secretion.
• These findings highlight the intricate regulation of enamel biomineralization by amelogenin processing.