Introduction:Amelogenin is a major component in the developing enamel matrix of secretory stage. However, its constructional details are unkown, although it involves securing space for crystal growth. It was inferred about a three-dimensional structure of the amelogenins formed based on their characteristics in solution. Methods:Three derivatives of porcine 173 amelogenin, 6kDa amelogenin (1-45), 13kDa amelogenin (46-148), and 20kDa amelogenin (1-148) were purified and their solubility behaviors in solution were examined. Results:The amelogenin molecule was suspected to be rod-like from the evidence that the 13kDa amelogenin and 20kDa amelogenin passed through a 3kDa cut-off ultra-filtration membrane, although the 20kDa amelogenin that passed through the membrane was small. The aggregation nature of amelogenin was located on the N-terminal side based on their solubility behaviors showing that the 20kDa and 6kDa amelogenins were aggregated and became insoluble in neutral buffer at 37°C, while the 13kDa amelogenin was soluble. Since the N-terminal sequence MPLPP (1-5) is the most hydrophobic in the molecule, the amelogenin may aggregate by hydrophobic bonds like a micelle with the N-terminal side in the center. The inferred structure indicates that complete 173 amelogenin micelles should be soluble in neutral solution during extraction, because around C-terminal end of the molecule is quite hydrophilic. This expectation was in conflict with the evidence that only 20% of the total amelogenins in newly formed enamel was soluble in neutral solution. The residual amelogenin was soluble in alkaline solution, and may bind by ionic bond to each other. This contradiction is solved by the inference that the C-terminal sequence KTKREEVD (166-173) of the 173 amelogenin may complementally bind by ionic bond against the reversed end of the molecule in another micelle. Conclusion:The amelogenin micelles construct a three-dimensional aggregate, and secure the space for crystal growth in the secretory stage enamel.

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