The long range goal of this Subproject is to utilize current information on structural characteristics of selected salivary molecules to design improved substances with enhanced biological activity. The starting point to be used in these """"""""structural mimicry"""""""" studies focuses on the major proline-rich glycoprotein from human parotid saliva (PRG). Among PRG's biological functions is the ability to interact with carbohydrate binding adhesins on the surface of Streptococcus sanguis. Both the primary structure of the oligosaccharide and the conformation of the peptide around the N-linked attachment point has been elucidated in our laboratory. While the structural specificity of the PRG-Streptococcus sanguis interaction has been demonstrated, the conformational basis for this specificity remains undefined. The present study will examine the role of peptide conformation around the N-glycosylation site of PRG in this specificity. Based on the beta-turn conformation we have reported, a neoglycopeptide will be synthesized using the intact (Asn/oligosaccharide) component of PRG and a cyclopeptide designed to exist as a beta-turn. The cyclopeptide has the advantage of greatly limiting the number of possible structures the corresponding linear peptide might have. Both the """"""""cycloneoglycopeptide"""""""" and its linear counterpart will be tested for binding affinity with Streptococcus sanguis after labeling the peptide moiety with 125I. The structures of both the cyclopeptide and peptide and the cycloneoglycopeptide and neoglycopeptide will be elucidated using x-ray crystallography, nuclear magnetic resonance spectroscopy (NMR) and computer modeling. Alteration of the beta-turn type will then be induced by substitution of D-amino acid isomers in the cycloneoglycopeptides. Following this, additional bacterial binding assays will be carried out. This methodology will allow a direct correlation of biological activity with a given conformation of peptide, thus defining this aspect of the cycloneoglycopeptide as to its relative importance in the PRG-Streptococcus sanguis interactions. It is anticipated that these analogs will have a biological potency at least equal to that of the native PRG molecule since we are in effect reconstructing a minimum functional domain. The information which can be obtained may provide a rationale for development of artificial salivas which could selectively modulate the oral flora.
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