Anti-peptide antibodies reactive with epitopic domains of porcine amelogenins at the C-terminus

This was an immunological investigation of the processing of porcine amelogenins in situ. Rabbit and rat anti-peptide sera reacted specifically with the hydrophilic segment of the intact amelogenins at the C-terminus. The immunogens used were the synthetic peptides: (a) C13 composed of PATDKTKREEVDC and (b) C25 composed of MQSLLPDLPLEAWPATDKTKREEVD. These peptides correspond to the C-terminal 12- and 25-residue segments of porcine amelogenin, respectively. Cystine was introduced at the C-terminus of C12 for KLH-binding (C13). Western blot analysis disclosed that: (i) both rabbit and rat anti-C13 sera reacted selectively with the 25-kDa porcine amelogenin and three other minor components (27, 22 and 18 kDa); (ii) anti-C25 peptide sera, additionally, reacted with the 23-kDa amelogenins (a degradation derivative of the 25-kDa protein, lacking the 12-residue segment at the C-terminus) and as trace components, 20-, 16- and 14-kDa moieties. Importantly, all the proteins reactive with the anti-C13 serum were concentrated in the outer secretory enamel adjacent to the ameloblasts, decreasing significantly in the underlying inner secretory enamel. Immunohistochemical studies applying the anti-peptide sera to the developing tooth germs of a minipig also confirmed the localization of reactivity in the outer secretory region. Neither anti-peptide serum reacted with porcine non-amelogenins, serum proteins nor dentine matrix proteins at the dilutions tested. However, it was found that both the anti-C13 and C25 sera reacted with human keratin. The overall results indicate that: (a) the last 25-amino acid residue segment of porcine amelogenin contains at least two epitopes at the C-terminus; (b) porcine amelogenesis may include the secretion of multiple amelogenins; and (c) the cleavage of the epitope(s) in the last 12-residue segment occurs shortly after secretion of the intact amelogenins.