Effects of bovine amelogenins on the crystal morphology of octacalcium phosphate in a model system of tooth enamel formation

Abstract

Amelogenins are the major protein component of the extracellular matrix of developing dental enamel and are believed to play critical roles in controlling the growth of enamel crystallites by providing the appropriate structural framework within which the crystallites initiate and grow. Effects of bovine amelogenins on the growth of octacalcium phosphate (OCP) crystals were evaluated in a model system of tooth enamel formation, where ionic diffusion was controlled by a cation selective membrane and a dialysis membrane. Reactions were carried out at 37°C with and without 10% amelogenins in a small space between the membranes, using 10 mM Ca and PO 4 solutions adjusted at pH 6.5 as ionic sources. Some parallel reactions were carried out in 5% albumin and 10% gelatin for a comparison. While albumin and gelatin decreased the crystal size of OCP, the effect of amelogenins on the growth of OCP crystals was remarkable. Rod-like and prism-like OCP crystals were predominant in 10% amelogenins, while characteristic ribbon-like OCP grew without protein, and with gelatin and albumin. Moreover, protein adsorption was observed on the side faces of the crystals grown in amelogenins. The width to thickness ( W/ T) ratio of OCP crystals grown in amelogenins was significantly smaller than those of control OCP and OCP crystals grown in gelatin and albumin. Amelogenin suppressed the growth of OCP in the order, b-axis> c-axis> a-axis direction. These data suggest that interactions of amelogenins with OCP crystals are stronger on the (0 1 0) faces than those on the (1 0 0) faces. The interaction between amelogenins and OCP crystal is discussed from the view point of the crystal structure and hydrophobic nature of amelogenins. The present experiment suggests that the hydrophobic amelogenin proteins are involved in controlling biomineralization processes such as modulation of crystal morphology.