Peptidomics of potato protein hydrolysates: implications of post-translational modifications in food peptide structure and behaviour

Abstract

Post-translational modifications (PTMs) often occur in proteins and play a regulatory role in protein function. There is an increasing interest in the bioactivity of food protein-derived peptides, but the occurrence of PTMs and their influence on food peptide structure and behaviour remain largely unknown. In this study, the shotgun-based peptidomics strategy was used to identify the occurrence of PTMs in peptides generated from potato protein hydrolysis using digestive proteases. Diverse PTMs were found in the potato peptides, including acetylation of lysine, N-terminal of proteins and peptides, C-terminal amidation, de-amidation of asparagine/glutamine, methylation and trimethylation, methionine oxidation and N-terminal pyro-glutamyl residue formation. The modifications may have been formed naturally or as a result of chemical reactions during isolation and enzymatic processing of the potato proteins. Most of the PTMs were calculated to decrease the isoelectric point and increase molecular hydrophobicity of the peptides, which will influence their bioactivity while also potentially altering their solubility in an aqueous environment. This is the first study to unravel that food-derived peptides can be widely modified by PTMs associated with notable changes in peptide chemical properties. The findings have broader implications on the bioavailability, biomolecular interactions and biological activities of food peptides.

Keywords: bioactive peptides; food proteins; hydrophobicity; isoelectric point; post-translational modification.

Figure 1.

Histograms showing changes in peptide chemical property caused by PTMs. Effect of pyro-Glu formation (at N-terminal Gln) on (a) isoelectric point (pI) and (b) hydrophobicity (H_R). Effect of Asn de-amidation on (c) pI and (d) H_R. ΔpI, difference of pI value for modified peptide and that of unmodified peptide; ΔH_R, difference of relative hydrophobicity value of modified peptide and that of the unmodified peptide.

Figure 2.

Reaction schemes for the formation of PTMs: (a) Lys acetylation, (b) pyro-glutamylation, and (c) Asn de-amidation in peptides; (a) decreased peptide pI values, whereas (b) and (c) both decreased pI and increased hydrophobicity of the peptides.