SMALL-ANGLE X-RAY-SCATTERING AND COMPUTER-AIDED MOLECULAR MODELING STUDIES OF 20 KDA FRAGMENT OF PORCINE AMELOGENIN - DOES AMELOGENIN ADOPTAN ELONGATED BUNDLE STRUCTURE

Amelogenins, which are major matrix constituents in the developing too th, play a regulatory role in the process of enamel crystal formation, Porcine amelogenin with 173 amino acid residues is rich in proline, g lutamine, leucine, and histidine. We utilized the small-angle X-ray sc attering (SAXS) technique to examine the solution structure of porcine amelogenin, Samples used were two porcine amelogenins with apparent m olecular weights of 20 kDa (amino acids 1 to 148) and 13 kDa (amino ac ids 46 to 148) on SDS-PAGE. Prior to SAXS measurements, the protein sa mples were dissolved in 2% (v/v) acetic acid to give a concentration r ange up to 10 mg/ml, Comparison between Rg (the overall radius of gyra tion) and Re (the cross-sectional radius of gyration) revealed that th e 20 kDa amelogenin exists in this solution as asymmetric particles wi th a length of about 15 nm, presumably corresponding of dimers, Based on these experimental data and computer-aided molecular modeling studi es, we propose that the 20 kDa amelogenin adopts an elongated bundle s tructure which mainly consists of extended structures similar to polyp roline II and/or beta-strand, interspersed with beta-turn or loop.