Abstract
Saliva is an important determinant of oral health. Alterations in salivary composition can correlate with disease susceptibility and/or progression, making human saliva a promising source of novel diagnostic markers and therapeutic targets. Ongoing research is aimed at cataloguing the proteome of the secretions of the major salivary glands. The unusual compositions of salivary proteins (e.g., proline-rich proteins) and a wealth of post-translational modifications (glycosylation, phosphorylation and proteolytic processing) provide many analytical challenges and interesting findings. Like other body fluids such as serum, saliva contains a vast array of endogenous, low-molecular weight peptides, many of which have important biological functions. We applied an iTRAQ-driven approach to show diurnal variation of the relative abundance of individual peptide species, suggesting additional functional relevance. Recently, we devised a mass spectrometry-based technique to globally assess proteolytic activities in complex biological samples. Results from these studies suggest that functional peptidomics can play important roles in the biomarker discovery process.

Background
Markus Hardt received his Vordiplom degree from University of Tübingen (Germany) and his Ph.D. in biochemistry from Louisiana State University in the laboratory of Roger A. Laine. In 2002 he joined Susan J. Fisher's group at the University of California San Francisco for a postdoctoral fellowship in biomedical mass spectrometry and is currently an Assistant Research Scientist in the Department of Cell and Tissue Biology. Dr. Hardt's research interests focus on the application of mass spectrometry-based methods to the fields of proteomics, peptidomics and biomarker discovery.