Peptidase Substrates via Global Peptide Profiling

Peptide metabolism is a complex process involving many proteins working in concert. Mass spectrometry (MS)-based global peptide profiling of mice lacking dipeptidyl peptidase 4 (DPP4) identified endogenous DPP4 substrates and revealed an unrecognized pathway during proline peptide catabolism that interlinks aminopeptidase and DPP4 activities. Together, these studies elucidate specific aspects of DPP4-regulated metabolism and, more generally, highlight the utility of global peptide profiling for studying peptide metabolism in vivo. The prolyl peptidase family has emerged as an intriguing class of enzymes due to the development of DPP4 inhibitors as anti-diabetic drugs1. DPP4 regulates physiological processes through the regulation of peptide hormones, such as the insulinotropic hormone glucagon-like peptide 1 (GLP-1), by cleaving a dipeptide from the N terminus. There has been a great deal of recent interest in finding additional physiological roles for DPP4 through the identification of new endogenous substrates2. We reasoned that the application of a liquid chromatography-mass spectrometry (LC-MS)-based global peptide profiling approach could improve on existing in vitro methods by directly measuring changes in tissu