Amelogenin Interacts with Cytokeratin-5 in Ameloblasts during Enamel Growth

Center for Craniofacial Molecular Biology, School of Dentistry, University of Southern California, Los Angeles 90033-1004, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 06/2003; 278(22):20293-302. DOI: 10.1074/jbc.M211184200
Source: PubMed


The enamel protein amelogenin binds to GlcNAc (Ravindranath, R. M. H., Moradian-Oldak, R., and Fincham, A.G. (1999) J. Biol. Chem. 274, 2464-2471) and to the GlcNAc-mimicking peptide (GMp) (Ravindranath, R. M. H., Tam, W., Nguyen, P., and Fincham, A. G. (2000) J. Biol. Chem. 275, 39654-39661). The GMp motif in the N-terminal region of the cytokeratin 14 of ameloblasts binds to trityrosyl motif peptide (ATMP) of amelogenin (Ravindranath, R. M. H., Tam, W., Bringas, P., Santos, V., and Fincham, A. G. (2001) J. Biol. Chem. 276, 36586 - 36597). K14 (Type I) pairs with K5 (Type II) in basal epithelial cells; GlcNAc-acylated K5 is identified in ameloblasts. Dosimetric analysis showed the binding affinity of amelogenin to K5 and to GlcNAc-acylated-positive control, ovalbumin. The specific binding of [3H]ATMP with K5 or ovalbumin was confirmed by Scatchard analysis. [3H]ATMP failed to bind to K5 after removal of GlcNAc. Blocking K5 with ATMP abrogates the K5-amelogenin interaction. K5 failed to bind to ATMP when the third proline was substituted with threonine, as in some cases of human X-linked amelogenesis imperfecta or when tyrosyl residues were substituted with phenylalanine. Confocal laser scan microscopic observations on ameloblasts during postnatal (PN) growth of the teeth showed that the K5-amelogenin complex migrated from the cytoplasm to the periphery (on PN day 1) and accumulated at the apical region on day 3. Secretion of amelogenin commences from day 1. K5, similar to K14, may play a role of chaperone during secretion of amelogenin. Upon secretion of amelogenin, K5 pairs with K14. Pairing of K5 and K14 commences on day 3 and ends on day 9. The pairing of K5 and K14 marks the end of secretion of amelogenin.

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    • "The tri-tyrosyl motif has been shown to bind to a conserved N-acetyl-d-glucosamine mimicking sequence present in cytokeratin 14 (33) and N-acetyl-d-glucosamine residues on cytokeratin 5 (19). Amelogenin and cytokeratin 14 co-localize at the apical regions of ameloblasts and dissociate at the Tomes’ processes prior to secretion leading to suggestions of a possible role for cytokeratin 14 in chaperoning amelogenin during amelogenesis (19,33). Failure to bind cytokeratin 14 was demonstrated when the human P → T mutation was introduced into the amelogenin tri-tyrosyl motif or when all three tyrosine residues were replaced by phenylalanine (33). "
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