title: Evolutionary analysis of selective constraints identifies ameloblastin (AMBN) as a potential candidate for amelogenesis imperfecta.
abstract: BACKGROUND
  Ameloblastin (AMBN) is a phosphorylated, proline/glutamine-rich protein secreted during enamel formation. Previous studies have revealed that this enamel matrix protein was present early in vertebrate evolution and certainly plays important roles during enamel formation although its precise functions remain unclear. We performed evolutionary analyses of AMBN in order to (i) identify residues and motifs important for the protein function, (ii) predict mutations responsible for genetic diseases, and (iii) understand its molecular evolution in mammals.
  
  
  RESULTS
  In silico searches retrieved 56 complete sequences in public databases that were aligned and analyzed computationally. We showed that AMBN is globally evolving under moderate purifying selection in mammals and contains a strong phylogenetic signal. In addition, our analyses revealed codons evolving under significant positive selection. Evidence for positive selection acting on AMBN was observed in catarrhine primates and the aye-aye. We also found that (i) an additional translation initiation site was recruited in the ancestral placental AMBN, (ii) a short exon was duplicated several times in various species including catarrhine primates, and (iii) several polyadenylation sites are present.
  
  
  CONCLUSIONS
  AMBN possesses many positions, which have been subjected to strong selective pressure for 200 million years. These positions correspond to several cleavage sites and hydroxylated, O-glycosylated, and phosphorylated residues. We predict that these conserved positions would be potentially responsible for enamel disorder if substituted. Some motifs that were previously identified as potentially important functionally were confirmed, and we found two, highly conserved, new motifs, the function of which should be tested in the near future. This study illustrates the power of evolutionary analyses for characterizing the functional constraints acting on proteins with yet uncharacterized structure.
authors.affiliation: Institut des Sciences de l'Evolution, UMR 5554, CNRS, IRD, EPHE, Université de Montpellier, Montpellier, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Delsuc
authors.affiliation: Université Pierre et Marie Curie, UMR 7138 Evolution Paris-Seine, Paris, France.
authors.forename: Barbara
authors.initials: B
authors.lastname: Gasse
authors.affiliation: Université Pierre et Marie Curie, UMR 7138 Evolution Paris-Seine, Paris, France. jean-yves.sire@upmc.fr.
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Sire
mesh_terms: D000567:Amelogenesis Imperfecta / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D017124:Conserved Sequence; D003743:Dental Enamel / Q000378:metabolism; D003746:Dental Enamel Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D006801:Humans; D008322:Mammals / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D014176:Protein Biosynthesis; D021382:Protein Sorting Signals; D016415:Sequence Alignment
chemical_list: C490889:AMBN protein, human; D003746:Dental Enamel Proteins; D021382:Protein Sorting Signals