Structural Changes in Amelogenin upon Self-assembly and Mineral Interactions

Amelogenin, the major protein of forming dental enamel, plays a crucial role in the biomineralization of this tissue. Amelogenin is soluble at low pH and self-assembles to form higher order structures at physiological pH. To understand the mechanisms of its assembly and interactions with calcium phosphate mineral, we conducted FTIR spectroscopy (FTIRS) studies of pH-triggered assembly of recombinant porcine amelogenin rP172 and its interactions with mature hydroxyapatite and apatitic mineral formed in situ. Analysis of our data indicated that rP172 at pH 3.0 exists in an unfolded disordered state, while increases in pH led to structural ordering, manifested by increases in intra- and intermolecular beta-sheet structures and a decrease in random coil and beta-turns. Amelogenin assembled at pH 7.2 was also found to contain large portions of extended intramolecular beta-sheet and PPII. These FTIRS findings are consistent with those previously obtained with other techniques, thus verifying the validity of our experimental approach. Interestingly, interactions with mineral led to a reduction in protein structural organization. The findings obtained show that amelogenin has intrinsic structural flexibility to accommodate interactions with both forming and mature calcium phosphate mineral phases, providing new insights into the potential importance of amelogenin-mineral interactions in enamel biomineralization.