title: Protein Interaction between Ameloblastin and Proteasome Subunit α Type 3 Can Facilitate Redistribution of Ameloblastin Domains within Forming Enamel.
abstract: Enamel is a bioceramic tissue composed of thousands of hydroxyapatite crystallites aligned in parallel within boundaries fabricated by a single ameloblast cell. Enamel is the hardest tissue in the vertebrate body; however, it starts development as a self-organizing assembly of matrix proteins that control crystallite habit. Here, we examine ameloblastin, a protein that is initially distributed uniformly across the cell boundary but redistributes to the lateral margins of the extracellular matrix following secretion thus producing cell-defined boundaries within the matrix and the mineral phase. The yeast two-hybrid assay identified that proteasome subunit α type 3 (Psma3) interacts with ameloblastin. Confocal microscopy confirmed Psma3 co-distribution with ameloblastin at the ameloblast secretory end piece. Co-immunoprecipitation assay of mouse ameloblast cell lysates with either ameloblastin or Psma3 antibody identified each reciprocal protein partner. Protein engineering demonstrated that only the ameloblastin C terminus interacts with Psma3. We show that 20S proteasome digestion of ameloblastin in vitro generates an N-terminal cleavage fragment consistent with the in vivo pattern of ameloblastin distribution. These findings suggest a novel pathway participating in control of protein distribution within the extracellular space that serves to regulate the protein-mineral interactions essential to biomineralization.
authors.affiliation: Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California 90033.
authors.forename: Shuhui
authors.initials: S
authors.lastname: Geng
authors.affiliation: School of Dentistry, UCLA, Los Angeles, California 90095.
authors.forename: Shane N
authors.initials: SN
authors.lastname: White
authors.affiliation: Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California 90033.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Paine
authors.affiliation: Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California 90033. Electronic address: mlsnead@usc.edu.
authors.forename: Malcolm L
authors.initials: ML
authors.lastname: Snead
mesh_terms: D000565:Ameloblasts / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism; D003743:Dental Enamel / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D003746:Dental Enamel Proteins / Q000235:genetics / Q000378:metabolism*; D005109:Extracellular Matrix / Q000737:chemistry / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D015723:Gene Library; D043425:Glutamate Carboxypeptidase II / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007180:Incisor / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D009805:Odontogenesis / Q000235:genetics*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D020798:Two-Hybrid System Techniques
chemical_list: C490890:Ambn protein, mouse; D003746:Dental Enamel Proteins; D008562:Membrane Glycoproteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D043425:Glutamate Carboxypeptidase II; C579805:PSMA protein, mouse; D046988:Proteasome Endopeptidase Complex
keywords: 20S proteosome; ameloblastin; biomineralization; enamel microstructure pattern; extracellular matrix protein; proteasome subunit α type 3; protein-protein interaction; tooth; yeast two-hybrid