LECTIN-LIKE PROPERTIES OF AMELOGENINS

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DESCRIPTION (adapted from the Investigator's abstract): The long-term objective of this proposal is to determine the nature and function of amelogenins with sugar residues of other enamel proteins, and cell surface glycoconjugates. The central hypothesis is that amelogenins have lectin-like properties, which mediate functional protein-carbohydrate interactions with matrix glycoproteins or cell surface glycoconjugates within the matrix or at the dentine enamel junction (DEJ). Preliminary data from the Principal Investigator's laboratory have established the presence of and amelogenin glyco-binding motif located in the conserved amino terminal region of the molecule. Others have established that a mutation in this region of the amelogenin structure results in the clinical enamel defect; amelogenesis imperfecta. (Collier et al., 1997). To test this hypothesis the following five specific aims will be investigated. The first aim is to identify specific interactions between amelogenins and structural analogs of N-acetyl glucosamine (GlcNAc) and N-acetyl neuraminic acid (NeuAC) and their glycosidic linkages commonly found in mammalian glycoproteins and glycolipids. Agglutination and competitive inhibition studies of amelogenins with oligosaccharides and glycoconjugates. (2) To identify putative ligands for amelogenin-binding in the extracellular enamel matrix "non-amelogenin" glycoprotein fractions. The lectin histochemistry of non-amelogenin proteins and immunological and radiometric assessment of amelogenin binding to these proteins is studied. (3) To assess the influence of carbohydrate-amelogenin interactions on nanosphere formation. Conjugates of glycoproteins and amelogenins are studied employing electron and atomic-force microscopy. (4) To evaluate the effects of GlcNAc/NeuAc-rich non-amelogenins and glycoprotein analogs on biomineralization in the presence and absence of amelogenin in vitro. The effects of glycoconjugates and amelogenins of apatite biomineralization are assessed. (5) To develop a model for the recognition and binding of amelogenins with cell surface glycoconjugates of odontoblasts and ameloblasts and to determine the effects of amelogenin-derived peptides on amelogenesis in vitro. A fibroblast model is developed and cell-surface amelogenin interactions and the putative role of amelogenin peptides in a feedback-signaling pathway are investigated. These experiments are a logical extension of the newly identified lectin-like properties of amelogenins (Ravindranath et al. Submitted), which are postulated to play a functional role in normal enamel biomineralization.