Label-free proteomic approach to identification and quantification of proteins in animal tissue samples

Mass spectrometry–based proteomics is recognise as an useful procedure for large-scale identification and quantification of proteins in natural samples. Here, we present the label-free proteomic approach for liver tissue samples obtained from lambs fed with the diet enriched with inorganic compounds of Se(VI) and organic selenium compounds (selenomethionine in selenium yeast). The study aimed to examine how the presence of inorganic and organic forms of selenium in the lambs’ forage affects the expression of the proteins, in particular, those containing selenium. In the course of the study, protein tissue homogenates were in-solution digested by trypsin. Peptide analysis was performed using high-resolution electrospray mass spectrometer equipped with Orbitrap mass analyser coupled to ultra-high performance liquid chromatography (nano-UHPLC-ESI- (ORBITRAP)-MS/MS). Based on registered data, using the appropriate proteomic software (Mascot, MaxQuant) with access to the SwissProt protein database, qualitative and quantitative analysis of proteins was achieved.