Peptidomics of Peptic Digest of Selected Potato Tuber Proteins: Post-Translational Modifications and Limited Cleavage Specificity.

Bioinformatic tools are useful in predicting bioactive peptides from food proteins. This study was focused on using bioinformatics and peptidomics to evaluate the specificity of peptide release and post-translational modifications (PTMs) in a peptic digest of potato protein isolate. Peptides in the protein hydrolysate were identified by LC-MS/MS and subsequently aligned to their parent potato tuber proteins. Five major proteins were selected for further analysis, namely, lipoxygenase, α-1,4-glucan phosphorylase, annexin, patatin, and polyubiquitin, based on protein coverage, abundance, confidence levels, and function. Comparison of the in silico peptide profile generated with ExPASy PeptideCutter and experimental peptidomics data revealed several differences. The experimental peptic cleavage sites were found to vary in number and specificity from PeptideCutter predictions. Average peptide chain length was also found to be higher than predicted with hexapeptides as the smallest detected peptides. Moreover, PTMs, particularly Met oxidation and Glu/Asp deamidation, were observed in some peptides, and these were unaccounted for during in silico analysis. PTMs can be formed during aging of potato tubers, or as a result of processing conditions during protein isolation and hydrolysis. The findings provide insights on the limitations of current bioinformatics tools for predicting bioactive peptide release from proteins, and on the existence of structural modifications that can alter the peptide bioactivity and functionality.