title: Is the 32-kDa fragment the functional enamelin unit in all species?
abstract: Enamelin is an extracellular enamel matrix protein essential for normal amelogenesis. After secretion, porcine enamelin is processed to generate several enamelin-degradation products. The cumulative 32-kDa enamelin is the most abundant enamelin present, and various roles for this molecule have been suggested. However, the proteolytic cleavage sites in porcine enamelin that generate the 32-kDa enamelin are not conserved across species, and the 32-kDa enamelin analogue may not be present in all species. To explore this we studied rat enamelin biochemistry using western blotting with anti-peptide IgGs to porcine 32-kDa enamelin and to the putative rat 32-kDa enamelin analogue. The dominant enamelins in secretory-stage rat enamel migrated at around 60-70 kDa. In contrast, the dominant enamelins in secretory-stage porcine enamel migrated at around 32 kDa. In contrast, secretory-stage porcine-enamel enamelins were dominated by the 32-kDa enamelin. Rat enamelin was completely removed from maturation-stage enamel without any accumulation of 32-kDa enamelin. We suggest that a discrete 32-kDa enamelin is not essential for normal amelogenesis in all species, and in pig it may be a processing product of a larger functional enamelin molecule. The pig may be an atypical model in terms of enamelin biochemistry and function, and caution should be exercised when assigning functional roles to the 32-kDa enamelin as a discrete enamel matrix entity.
authors.affiliation: Department of Oral Biology, Leeds Dental Institute, University of Leeds, Leeds, UK. S.J.Brookes@Leeds.ac.uk
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Brookes
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Kingswell
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Barron
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Dixon
authors.forename: Jennifer
authors.initials: J
authors.lastname: Kirkham
mesh_terms: D000566:Amelogenesis; D000818:Animals; D003746:Dental Enamel Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry / Q000502:physiology; D011499:Protein Processing, Post-Translational; D059748:Proteolysis; D051381:Rats; D017208:Rats, Wistar; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D034421:Sus scrofa
chemical_list: D003746:Dental Enamel Proteins; D010446:Peptide Fragments; C038456:tuftelin