SOLID STATE STRUCTURAL ANALYSIS OF SALIVARY PROTEINS

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The broad and long-term objective of the proposed study is to elucidate the physical-chemical and conformational basis for the biological functions of salivary molecules bound to tooth-like model surfaces. These types of investigations are required if one is to understand the molecular mechanisms responsible for the biological activities of salivary molecules in determining health nad disease. The specific aim of the current proposal is to obtain data from cross-polarization magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS NMR) on a well- characterized salivary peptide model system. Specifically, the multiply occurring nonapeptide segment (NH2-G-P-P-P-H-P-G-K-P-COOH or "PRG9"), derived from the proline-rich glycoprotein (PRG) found in human parotid saliva, will be used for this purpose. PRG9 is known to occur in the acquired enamel pellicle, binds calcium and acts as one of the primary structural determinants in native PRG. Also, the major solution-state conformations and substrate-bound physical-chemical properties of PRG9 have already been discerned. In order to achieve the stated specific aim, the carbon-13 (C13) solution-state NMR spectra of solubilized PRG9 will first be obtained. Subsequently, the C13 CP/MAS NMR spectra of "free" of "unbound" solid PRG9 and hydroxyapatite-bound peptide will be collected. A novel and necessary peak assignment strategy to be used involves collecting spectra of all PRG9's pertinent "subfragments" sequentially, starting with the N-terminal dipeptide through the intact nonapeptide, such that a complete library of resonance locations will be constructed. This is required for two reasons. First, the solid-state CP/MAS NMR experiment removes dipolar couplings and prohibits the use of experiments commonly used in solution-state NMR for spectral peak assignment (e.g. off-resonance decoupling, heteronuclear mapping, etc.). Second, the absence of NH peaks from proline disallows sequence-specific resonance assignments of these residues in the solution-state. The subfragment peptides will have the following amino acid sequences: (i) NH2-G-P-COOH, (ii) NH2-G-P-P-COOH, (iii) NH2-G-P-P-P-COOH, (iv) NH2-G-P-P-P-H-COOH, (v) NH2-G-P-P-P-H-P- COOH,(vi) NH2-G-P-P-P-H-P-G-COOH, and (vii) NH2-G-P-P-P-H-P-G-K-COOH. The solution-state, "free" solid-state and hydroxyapatite-adsorbed peptide NMR spectra will then be compared to each other, as well as data found in the literature. Assessment of PRG9 conformation will be based upon published C12 NMR spectra of peptides in known informational states. These results will represent the first structural analyses of salivary peptides at atomic resolution in the solid-state, and provide information sa to the conformational changes occurring upon substrate binding.