Proteolytic activity of opossum tooth extracts.

Amelogenins are the main component of the developing enamel matrix. In placental mammals, amelogenins are rapidly cleaved following their secretion. HPLC fractionation of tooth extracts produces a complex chromatographic profile. The fractions are rich in amelogenin cleavage products that generally retain the amino-terminus of the parent protein but have varying lengths of peptide removed from the original carboxyl-terminus. In contrast, HPLC fractionation of opossum tooth extracts produces a simple profile with a single major chromatographic peak. SDS-and Western blot analyses demonstrated that most of the amelogenin consisted of a prominent protein band that migrated at 28 kDa. Mass spectroscopy confirmed the presence of two uncleaved, alternatively spliced forms of opossum amelogenin, Op202 and Op57, but did not detect major amelogenin cleavage products evident in tooth extracts from placental mammals. Amino acid composition analysis supported the conclusion that uncleaved amelogenin is the major component in the developing enamel matrix. Enzymogram analyses using gelatin, casein and recombinant amelogenin as substrates, comparing porcine, rat and opossum tooth extracts, suggested that fewer proteinases are present in opossum. These results identify potentially significant differences in the proteolytic processing of amelogenins between metatherian and eutherian mammals.