Journal of Dental Research, Vol 66, 462-466, Copyright © 1987 by International & American Associations for Dental Research Online Journals
Molecular basis of salivary proline-rich protein and peptide synthesis: cell-free translations and processing of human and macaque statherin mRNAs and partial amino acid sequence of their signal peptides
F. G. Oppenheim, D. I. Hay, D. J. Smith, G. D. Offner and R. F. Troxler
Acidic proline-rich phosphoproteins and phosphopeptides are abundant
components of parotid and submandibular salivary secretions in man and in
the subhuman primate, Macaca fascicularis. The major acidic proline-rich
proteins and the proline-rich phosphopeptide, statherin, of man and
macaques have been shown to be potent inhibitors of calcium phosphate
precipitation and are thought to function in the oral environment by
maintaining saliva supersaturated with respect to calcium phosphate salts.
Little is known about the biosynthesis of these proline-rich
phosphoproteins and peptides, and the aim of the present work was to
determine the structural relationship between statherin precursors and
native human and macaque statherin. RNA was isolated from human
submandibular gland, and poly(A+) mRNA was selected by affinity
chromatography on oligo(dT) cellulose and translated in a reticulocyte
lysate. Electrophoretic analysis of the translation products revealed that
this mRNA directed the synthesis of a large number of polypeptides with Mrs
ranging from 5000 to 70,000. Immunoprecipitates, prepared with an antiserum
directed against human statherin, contained a single component with a Mr of
7800, approximately 2000 daltons larger than native statherin.
Radiosequencing of the in vitro precursor of statherin in
immunoprecipitates demonstrated the presence of a 19-residue signal
peptide. These results suggest that statherin is derived from a unique
structural gene, and does not result from proteolytic processing of a large
polyprotein precursor.
