Fig. 1.

Gene structure and proteolytic cleavage products of ameloblastin. a: Human AMBN. Gene structure based on the reference gene sequence (Genbank accession No NC_000004.11). Exons are numbered from 1 to 13. Two translation initiation sites (ATG) are found: in exon 1 and exon 2. The untranslated regions are in light grey. The number of base pairs (bp) is indicated above each exon. The nomenclatural counts of encoded amino acids (p.), cDNA bp (c.) and gDNA bp (g.) are also indicated below each exon. Introns are symbolized by the black lines (not at scale) with the nucleotide number indicated above. The stop codon (TGA) is located in exon 13. b: Porcine AMBN. Diagram showing the cleavage products and their corresponding location on the protein sequence (after [6, 20, 29, 99, 101, 116]). Top: AMBN exons. Note that exons 8 and 9, which encode 26 residues in humans are lacking in porcine AMBN. Bottom: AMBN protein including either the 26 residues forming the signal peptide-SP (1–421) or not (1–395). Several remarkable residues were identified: two phosphorylated residues (S¹⁷, T²⁵¹) and two putatively phosphorylated residues (S²⁰⁹, S²¹⁰), two O-glycosylated residues (S⁸⁶, T³⁶¹), two hydroxylated prolines (P¹¹, P³²⁴), and the proline-rich region. The secreted protein has an apparent molecular weight of 62 kDa; cleavage sites leading to various AMBN fragments found in vivo are indicated in roman characters, two MMP20 cleavage sites found in in vitro studies are in italics