The COOH terminus of the amelogenin, LRAP, is oriented next to the hydroxyapatite surface.
The organic matrix in forming enamel consists largely of the amelogenin protein self-assembled into nanospheres that are necessary to guide the formation of the unusually long and highly ordered hydroxyapatite (HAP) crystallites that constitute enamel. Despite its ability to direct crystal growth, the interaction of the amelogenin protein with HAP is unknown. However, the demonstration of growth restricted to the c-axis suggests a specific protein-crystal interaction, and the charged COOH terminus is often implicated in this function. To elucidate whether the COOH terminus is important in the binding and orientation of amelogenin onto HAP, we have used solid state NMR to determine the orientation of the COOH terminus of an amelogenin splice variant, LRAP (leucine-rich amelogenin protein), which contains the charged COOH terminus of the full protein, on the HAP surface. These experiments demonstrate that the methyl 13C-labeled side chain of Ala46 is 8.0 A from the HAP surface under hydrated conditions, for the protein with and without phosphorylation. The experimental results provide direct evidence orienting the charged COOH-terminal region of the amelogenin protein on the HAP surface, optimized to exert control on developing enamel crystals.
Pacific Northwest National Laboratory, Richland, Washington 99352, USA. wendy.shaw@pnl.gov
Wendy J
WJ
Shaw
Allison A
AA
Campbell
Michael L
ML
Paine
Malcolm L
ML
Snead
D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001672:Biocompatible Materials / Q000737:chemistry*; D002417:Cattle; D003743:Dental Enamel / Q000737:chemistry; D003746:Dental Enamel Proteins / Q000737:chemistry* / Q000378:metabolism; D017886:Durapatite / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D008969:Molecular Sequence Data; D010452:Peptide Biosynthesis; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
D001672:Biocompatible Materials; D003746:Dental Enamel Proteins; C067432:leucine-rich amelogenin peptide; D017886:Durapatite; D000409:Alanine