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J Biol Chem. 2015 Aug 21;290(34):20661-73. doi: 10.1074/jbc.M115.640185. Epub 2015 Jun 12.

Protein Interaction between Ameloblastin and Proteasome Subunit α Type 3 Can Facilitate Redistribution of Ameloblastin Domains within Forming Enamel.

Author information

1
From the Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California 90033 and.
2
the School of Dentistry, UCLA, Los Angeles, California 90095.
3
From the Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California 90033 and mlsnead@usc.edu.

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.

KEYWORDS:

20S proteosome; ameloblastin; biomineralization; enamel microstructure pattern; extracellular matrix protein; proteasome subunit α type 3; protein-protein interaction; tooth; yeast two-hybrid

PMID:
26070558
PMCID:
PMC4543628
DOI:
10.1074/jbc.M115.640185
[Indexed for MEDLINE]
Free PMC Article

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