Role of hydrophobicity in food peptide functionality and bioactivity

Peptides are important compounds used in the development of functional biomaterials, functional foods and nutraceuticals. The functional and bioactive properties of peptides are directly linked to their structural features, including molecular size, presence or absence of charges, amino acid sequence, hydrophobicity, and hydrophilicity. The role of peptide structures in their bioactivities and functionalities is still emerging. Some bioactive peptides have undesirable taste, which can influence consumer interests in novel peptide-based food applications. In this review, we discussed the role of peptide hydrophobicity in their bioavailability, bioactivity, bitterness property, emulsion stability, aggregation and self-assembly for application in novel food formulations and nutraceutical/ drug delivery.

Peptidomics analysis of potato protein hydrolysates: post-translational modifications and peptide hydrophobicity

Post-translational modifications (PTMs) often <a></a><a>occur in proteins</a> and play a regulatory role in protein function. However, the role of PTMs in food-derived peptides remains largely unknown. The shotgun peptidomics strategy was employed to identify PTMs in peptides from potato protein hydrolysates. Various hydrophobicity-inducing PTMs were found to be located in different potato peptides, <i>e.g</i>. acetylation of lysine, N-terminal of proteins and peptides, C-terminal amidation, asparagine/glutamine deamidaiton, methylation and trimethylation, methionine oxidation, and N-terminal pyro-glutamate formation. Some of the PTMs are likely formed by chemical reactions that occur during isolation and proteolytic processing of potato proteins. The PTMs enhance peptide hydrophobicity, which can improve bioactivity, decrease solubility and increase the bitterness of peptides. This is the first report that food-derived peptides are widely modified by various PTMs associated with hydrophobicity-inducing structural changes. This finding will enhance understanding of the behaviour of bioactive peptides in biological matrices.

Signal Peptide Hydrophobicity Modulates Interaction with the Twin-Arginine Translocase

ABSTRACT The general secretory pathway (Sec) and twin-arginine translocase (Tat) operate in parallel to export proteins across the cytoplasmic membrane of prokaryotes and the thylakoid membrane of plant chloroplasts. Substrates are targeted to their respective machineries by N-terminal signal peptides that share a tripartite organization; however, Tat signal peptides harbor a conserved and almost invariant arginine pair that is critical for efficient targeting to the Tat machinery. Tat signal peptides interact with a membrane-bound receptor complex comprised of TatB and TatC components, with TatC containing the twin-arginine recognition site. Here, we isolated suppressors in the signal peptide of the Tat substrate, SufI, that restored Tat transport in the presence of inactivating substitutions in the TatC twin-arginine binding site. These suppressors increased signal peptide hydrophobicity, and copurification experiments indicated that they restored binding to the variant TatBC complex. The hydrophobic suppressors could also act in cis to suppress substitutions at the signal peptide twin-arginine motif that normally prevent targeting to the Tat pathway. Highly hydrophobic variants of the SufI signal peptide containing four leucine substitutions retained the ability to interact with the Tat system. The hydrophobic signal peptides of two Sec substrates, DsbA and OmpA, containing twin lysine residues, were shown to mediate export by the Tat pathway and to copurify with TatBC. These findings indicate that there is unprecedented overlap between Sec and Tat signal peptides and that neither the signal peptide twin-arginine motif nor the TatC twin-arginine recognition site is an essential mechanistic feature for operation of the Tat pathway. IMPORTANCE Protein export is an essential process in all prokaryotes. The Sec and Tat export pathways operate in parallel, with the Sec machinery transporting unstructured precursors and the Tat pathway transporting folded proteins. Proteins are targeted to the Tat pathway by N-terminal signal peptides that contain an almost invariant twin-arginine motif. Here, we make the surprising discovery that the twin arginines are not essential for recognition of substrates by the Tat machinery and that this requirement can be bypassed by increasing the signal peptide hydrophobicity. We further show that signal peptides of bona fide Sec substrates can also mediate transport by the Tat pathway. Our findings suggest that key features of the Tat targeting mechanism have evolved to prevent mistargeting of substrates to the Sec pathway rather than being a critical requirement for function of the Tat pathway.

Signal peptide hydrophobicity modulates interaction with the twin-arginine translocase

The general secretory pathway (Sec) and twin-arginine translocase (Tat) operate in parallel to export proteins across the cytoplasmic membrane of prokaryotes and the thylakoid membrane of plant chloroplasts. Substrates are targeted to their respective machineries by N-terminal signal peptides that share a common tripartite organization, however Tat signal peptides harbor a conserved and almost invariant arginine pair that are critical for efficient targeting to the Tat machinery. Tat signal peptides interact with a membrane-bound receptor complex comprised of TatB and TatC components, with TatC containing the twin-arginine recognition site. Here we isolated suppressors in the signal peptide of the Tat substrate, SufI, that restored Tat transport in the presence of inactivating substitutions in the TatC twin-arginine binding site. These suppressors increased signal peptide hydrophobicity, and co-purification experiments indicated that they restored binding to the variant TatBC complex. The hydrophobic suppressors could also act in cis to suppress substitutions at the signal peptide twin-arginine motif that normally prevent targeting to the Tat pathway. Highly hydrophobic variants of the SufI signal peptide containing four leucine substitutions retained the ability to interact with the Tat system. The hydrophobic signal peptides of two Sec substrates, DsbA and OmpA, containing twin lysine residues, were shown to mediate export by the Tat pathway and to co-purify with TatBC. These findings indicate that there is unprecedented overlap between Sec and Tat signal peptides and that neither the signal peptide twin-arginine motif nor the TatC twin-arginine recognition site are essential mechanistic features for operation of the Tat pathway.ImportanceProtein export is an essential process in all prokaryotes, The Sec and Tat export pathways operate in parallel, with the Sec machinery transporting unstructured precursors and the Tat pathway transporting folded proteins. Proteins are targeted to the Tat pathway by N-terminal signal peptides that contain an almost invariant twin-arginine motif. Here we make the surprising discovery that the twin-arginines are not essential for recognition of substrates by the Tat machinery, and that this requirement can be bypassed by increasing the signal peptide hydrophobicity. We further show that signal peptides of bona fide Sec substrates can also mediate transport by the Tat pathway. Our findings suggest that key features of the Tat targeting mechanism have evolved to prevent mis-targeting of substrates to the Sec pathway rather than being a critical requirement for function of the Tat pathway.

Peptidomics analysis of potato protein hydrolysates: post-translational modifications and peptide hydrophobicity

Post-translational modifications (PTMs) often <a></a><a>occur in proteins</a> and play a regulatory role in protein function. However, the role of PTMs in food-derived peptides remains largely unknown. The shotgun peptidomics strategy was employed to identify PTMs in peptides from potato protein hydrolysates. Various hydrophobicity-inducing PTMs were found to be located in different potato peptides, <i>e.g</i>. acetylation of lysine, N-terminal of proteins and peptides, C-terminal amidation, asparagine/glutamine deamidaiton, methylation and trimethylation, methionine oxidation, and N-terminal pyro-glutamate formation. Some of the PTMs are likely formed by chemical reactions that occur during isolation and proteolytic processing of potato proteins. The PTMs enhance peptide hydrophobicity, which can improve bioactivity, decrease solubility and increase the bitterness of peptides. This is the first report that food-derived peptides are widely modified by various PTMs associated with hydrophobicity-inducing structural changes. This finding will enhance understanding of the behaviour of bioactive peptides in biological matrices.