Profiling human saliva endogenous peptidome via a high throughput MALDI-TOF-TOF mass spectrometry

Establishment of a saliva protein/peptide signature will provide important information for clinical diagnostics and prognosis of human disease. We digested human whole saliva with trypsin to create a tryptic digest salivary peptidome. Proteins/peptides were subsequently identified by high throughput tandem mass spectrometry in conjunction with database searching. Sixty-three saliva peptides corresponding to twenty-two saliva proteins were identified. Thirty of sixty-three saliva peptides with non-specific tryptic cleavage sites were derived from proline-rich proteins, mucin 7, statherin and collagen. Several peptides derived from proline-rich proteins exhibit proline (Pro) - glutamine (Gln) C-termini (-PQ C-termini). Seven peptides with -PQ C-termini were identified in undigested whole saliva, suggesting that peptides with -PQ C-termini indigenously exist in human saliva. Peptides with -PQ C-termini are known to bind oral bacteria and exhibit properties characteristic of innate-immunity peptides. Thus, a saliva peptidome containing peptides with -PQ C-termini, as presented here, may reinforce the development of innate-immunity-related disease monitoring using non-invasive saliva samples and mass spectrometry-based techniques.