Elongated Growth of Octacalcium Phosphate Crystals in Recombinant Amelogenin Gels under Controlled Ionic Flow

Amelogenin proteins constitute the primary structural entity of the extracellular protein framework of the developing enamel matrix. Recent data on the interactions of amelogenin with calcium phosphate crystals support the hypothesis that amelogenins control the oriented and elongated growth of enamel carbonate apatite crystals. To exploit further the molecular mechanisms involved in amelogenin-calcium phosphate mineral interactions, we conducted in vitro experiments to examine the effect of amelogenin on synthetic octacalcium phosphate (OCP) crystals. A 10% (wt/vol) recombinant murine amelogenin (rM179, rM166) gel was constructed with nanospheres of about 10- to 20-nm diameter, as observed by atomic force microscopy. The growth of OCP was modulated uniquely in 10% rM179 and rM166 amelogenin gels, regardless of the presence of the hydrophilic C-terminal residues. Fibrous crystals grew with large length-to-width ratio and small width-to-thickness ratio. Both rM179 and rM166 enhanced the growth of elongated OCP crystals, suggesting a relationship to the initial elongated growth of enamel crystals.