Amelogenin Processing
by MMP-20 Prevents Protein Occlusion
Inside Calcite Crystals
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Abstract
Calcite crystals were grown in the presence of full-length
amelogenin
and during its proteolysis by recombinant human matrix metalloproteinase
20 (rhMMP-20). Recombinant porcine amelogenin (rP172) altered the
shape of calcite crystals by inhibiting the growth of steps on the
{104} faces and became occluded inside the crystals. Upon co-addition
of rhMMP-20, the majority of the protein was digested resulting in
a truncated amelogenin lacking the C-terminal segment. In rP172-rhMMP-20
samples, the occlusion of amelogenin into the calcite crystals was
drastically decreased. Truncated amelogenin (rP147) and the 25-residue
C-terminal domain produced crystals with regular shape and less occluded
organic material. Removal of the C-terminal diminished the affinity
of amelogenin to the crystals and therefore prevented occlusion. We
hypothesize that hydroxyapatite (HAP) and calcite interact with amelogenin
in a similar manner. In the case of each material, full-length amelogenin
binds most strongly, truncated amelogenin binds weakly, and the C-terminus
alone has the weakest interaction. Regarding enamel crystal growth,
the prevention of occlusion into maturing enamel crystals might be
a major benefit resulting from the selective cleavage of amelogenin
at the C-terminus by MMP-20. Our data have important implications
for understanding the hypomineralized enamel phenotype in cases of <i>amelogenesis imperfecta</i> resulting from MMP-20 mutations
and will contribute to the design of enamel inspired biomaterials