Molecular conformation of porcine amelogenins and its significance in protein-mineral interaction: 1H-NMR photo-CIDNP study.

The present 1H-nmr study was undertaken to investigate the molecular structure of porcine amelogenins in solution using photo-CIDNP (chemically induced dynamic nuclear polarization). The proteins of interest were the parent 25 kD amelogenin consisting of 173 amino acid residues and its degraded products having molecular masses of 23 kD, 20 kD, 13 kD and 5 kD on SDS-PAGE. From the recorded 1H-nmr and photo-CIDNP spectra, it was found that: 1) the Trp161 at the C-terminus of the 25 kD protein showed a stronger photo-CIDNP effect than the other two Trp25,45 at the N-terminus; 2) Tyr residues at the N-terminus of the 25 kD and 20 kD amelogenins gave rise to the strong peak around 6.8 ppm, indicating that at least some of the six Tyr residues are surface residues; and 3) the accessibility of His residues was quite different between the 13 kD fragment and the 25 kD and 20 kD proteins. These results suggest that the hydrophilic segment at the C-terminus is most likely exposed on the molecular surface and that the molecular structure of the amelogenin in solution may change substantially by the cleavage of the segments at the N- and C-termini.