Quantitative proteomics and SWATH-MS to elucidate peri-receptor mechanisms in human salt taste sensitivity

Recently, studies on human salt taste sensitivity demonstrated that sodium chloride (NaCl) sensitive and non-sensitive subjects differed in their salivary proteome and, in particular, in endopeptidase activity. In order to investigate individual's NaCl sensitivity and the role of endoprotease activity in salt taste perception, 20 panellists were classified according to NaCl sensitivity and saliva samples collected. A targeted protein quantitation by means of selected-reaction-monitoring (SRM) mass spectrometry and stable-isotope incorporation revealed the joint abundance of lysozyme C and lipocalin-1 to be indicative for non-sensitive subjects. Sensory studies performed after oral challenge with the serine-type endopeptidase trypsin demonstrated a salt enhancing effect which was assumed to be due to an in-vivo generation of salt-modulating peptides as shown by LC-SWATH-MS. Amongst those, the tetrapeptide PLWR was found to elicit salty taste enhancing activity above an extraordinarily low taste threshold concentration of 6.5 μmol/L.