Analysis of the Human Salivary Peptidome by Differential Peptide Display and LC-MS/MS Overview Sequencing

In recent years interest in the characterization of the human salivary proteome has increased in order to explore its diagnostic potential. Major constituents of human saliva are highly polymorphic proteins that may have biological roles in oral lubrication and protection, e.g. proline-rich proteins (PRPs), statherins, histatins and cystatins. Interestingly, many of theses proteins are rapidly degraded in the oral cavity by host- and bacteria- or viral-derived proteases. Thus, comprehensive analysis of peptides up to 15 kDa (peptidomics) of whole saliva may yield basic information on proteolytic patterns. By employing a LC-ESI-MS/MS approach a total of 107 native peptides from 17 distinct protein precursors was identified from whole saliva. Subsequently the catalog of peptides was used to analyze inter-individual differences in saliva samples from four donors by differential peptide display technology. Genetic polymorphisms were found in peptides from the PRB4M_HUMAN and PROL4_HUMAN precursors. Analysis of the proposed N- and C-termini of the peptides revealed frequent cleavage after Lys or Arg which is characteristic for salivary kallikrein enzymes. Furthermore, we highlight the cleavage motif Gln/Gly in the PRP-C precursor, which suggests a new proteolytic pattern in saliva.