Trypsin as a Proteomic Probe for Assessment of Food Protein Digestibility in Relation to Chemical and Post-translational Modifications

Post-translational modifications (PTMs) occur in many forms and shapes, widely influencing protein behavior. High-resolution tandem mass spectrometry (HRMS/MS), coupled with dedicated engines for the identification of unspecified PTMs, is a powerful method for their mapping. A majority of proteomic experiments utilize trypsin for digestion, which cleaves the C-terminal peptide bonds of arginine (Arg) and lysine (Lys) amino acids with high catalytic efficiency and selectivity, unless they are followed with proline. At the same time, Arg and Lys residues are frequently modified during food processing by heat and non-thermal treatments, causing oxidation, carbamylation, and various forms of side chain carbonylation, including the other common PTMs (methylation, acetylation, etc.). Consequently, we explored the possibility to re-assess already generated proteomic data (food protein/allergen tryptic peptides) with respect to the possible modulation of the tryptic intestinal digestion pattern caused by PTMs incorporated at Arg and Lys residues. However, most of the proteomic bottom-up experiments are run with porcine trypsin that has been reductively methylated to increase its stability and minimize autoproteolytic effects. Therefore, in this chapter, the utility of the aforementioned idea was explored, by reviewing the differences in structure, affinity, specificity, and catalytic efficiency of trypsin, primarily from porcine, bovine and human species. Porcine trypsin either from pancreas or in recombinant form showed superior performance compared to human and bovine tryptic counterparts. In addition, set of software tools for identification and analyses of PTMs was reviewed with the aim to isolate those capable of in-depth PTMs profiling and their simultaneous relative quantification, such as PEAKS PTM (PEAKS Studio, Bioinformatics Solution Inc., Ontario Canada). Based on our preliminary experimental results, conclusion is that the proposed idea is plausible, because if potential hindrance effects caused by PTMs are observed with porcine trypsin, then they can be just augmented within human intestinal digestion, with respect to inferior performance of human trypsin