Solid state NMR of salivary calculi: Proline-rich salivary proteins, citrate, polysaccharides, lipids, and organic-mineral interactions

Solid state NMR (ssNMR) can characterize mineral (P-31) and organic (C-13) components of human salivary stones (n = 8). All show apatitic P-31 spectra. C-13 ssNMR indicates more protein, of more consistent composition, than apatitic uroliths, with prominent signals from Tyr, Phe, and His. Citrate and lipids, identified by dipolar dephasing (DD), and polysaccharides are also observable in varying amounts. C-13{P-31} rotational echo double resonance (C-13{P-31} REDOR) identifies carbon atoms in close (< ca. 0.5 nm) proximity to phosphorus and therefore probably binding with mineral. Citrate, sugar, and carboxylate signals exhibit strong C-13{P-31} REDOR effects, also observed for signals between 50 and 60 ppm, from protein alpha-carbons and, possibly, phosphoserines and phospholipids, and sometimes for a 35-40 ppm envelope containing Asp-C beta and Glu-C gamma signals. Amino acid analysis indicates high proline and aromatic content. C-13 ssNMR and amino acid analyses are consistent with the preponderance of proline-rich salivary proteins such as statherin. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.