Identification of stool proteins in C57BL/6J mice by two-dimensional gel electrophoresis and MALDI-TOF mass spectrometry

Gastrointestinal disease is a major cause of mortality in humans and animals, and the detection of disease-associated protein in stool is an established diagnostic method in this context. Yet, no data currently exists about the protein composition of mammalian faeces. Using a newly developed two-dimensional (2D) gel method, 28 of the most abundant proteins in murine faeces were identified. Mammalian faeces contains protein from multiple species (from the individual, from gastrointestinal bacteria, from food, etc.). Yet, it was found that the majority of mouse stool proteins were of mouse origin, with a minority of proteins being derived from food (in particular soybean glycinin and conglycinin) and bacteria (flagellin). Most mouse proteins were proteases and saccharidases derived from the exocrine pancreas. In addition, two unexpected mouse proteins were identified: one was a newly described mucin-like protein from intestinal goblet cells (FcγBP); the other was the secreted form of carbonic anhydrase (type VI) from salivary gland. The data suggest that 2D analysis of faecal protein is likely to provide meaningful information about the physiological stage of the gastrointestinal tract. Compared with studies based on biopsies, faecal protein analysis may reduce the number of laboratory animals, and might also allow quicker bridging from animal studies to humans, where biopsy material is more difficult to obtain and is less relevant for general practice use.