Amelogenin-cytokeratin 14 interaction in ameloblasts during enamel formation.
The enamel protein amelogenin binds 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 is found in the N-terminal region of CK14, a differentiation marker for ameloblasts. The binding affinity of CK14 and amelogenin was confirmed by dosimetric binding of CK14 to recombinant amelogenin (rM179), and to the tyrosine-rich amelogenin polypeptide. The specific binding site for CK14 was identified in the amelogenin trityrosyl motif peptide (ATMP) of tyrosine-rich amelogenin polypeptide and specific interaction between CK14 and [(3)H]ATMP was confirmed by Scatchard analysis. Blocking rM179 with GlcNAc, GMp, or CK14 with ATMP abrogates the CK14-amelogenin interaction. CK14 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. Morphometry of developing teeth distinguished three phases of enamel formation; growth initiation phase (days 0-1), prolific growth phase (days 1-7), and growth cessation phase (post-day 7). Confocal microscopy revealed co-assembly of CK14/amelogenin in the perinuclear region of ameloblasts on day 0, migration of the co-assembled CK14/amelogenin to the apical region of the ameloblasts from day 1, reaching a peak on days 3-5, and a collapse of the co-assembly. Autoradiography with [(3)H]ATMP and [(3)H]GMp corroborated the dissociation of the co-assembly at the ameloblast Tomes' process. It is proposed that CK14 play a chaperon role for nascent amelogenin polypeptide during amelogenesis.
Ravindranath
R M
RM
Center for Craniofacial Molecular Biology, School of Dentistry, University of Southern California, Los Angeles, California 90033, USA. rravindr@hsc.usc.edu
Tam
W Y
WY
Bringas
P
P
Santos
V
V
Fincham
A G
AG
D000118:Acetylglucosaminidase / Q000494:pharmacology; D053523:Amelogenin; D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002478:Cells, Cultured; D003743:Dental Enamel / Q000196:embryology*; D003746:Dental Enamel Proteins / Q000737:chemistry* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D007633:Keratins / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D018613:Microscopy, Confocal; D008954:Models, Biological; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D011392:Proline / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011994:Recombinant Proteins / Q000378:metabolism; D013912:Threonine / Q000737:chemistry; D013997:Time Factors; D014443:Tyrosine / Q000737:chemistry
D053523:Amelogenin; C507200:Amelx protein, mouse; D003746:Dental Enamel Proteins; D010455:Peptides; D011994:Recombinant Proteins; D013912:Threonine; D014443:Tyrosine; D007633:Keratins; D011392:Proline; D000118:Acetylglucosaminidase