Identification of bioaccessible glycosylated neuroprotective peptides from brewer's spent yeast mannoproteins by in vitro and in silico studies

The aims of this work were to purify mannoproteins from brewer's spent yeast, to evaluate the neuroprotective and antioxidant properties of peptides generated by a simulated gastrointestinal digestion (SGID), and to identify the peptides responsible of acetylcholinesterase (AChE), tyrosinase (TYR), prolyl oligopeptidase (POP) and ABTS(+) inhibitory activity using tandem mass spectrometry and in silico analysis. Mannoproteins from brewer's spent yeast were purified using the simultaneous effect of ethanol and pH on protein solubility followed by ultrafiltration process (10 kDa). The retained fraction (> 10 kDa) showed 80.5 +/- 5.8 g protein 100 g(-1) solids, of which 71.2 +/- 1.0 g 100 g(-1) were mannoprotein. The SGID of isolated mannoproteins released peptides with AChE, TYR, POP and ABTS(+) inhibitory activity. Peptides released from mannoproteins showed strong inhibitory activity against TYR by diphenolase mechanism. These bioactivities were related to low MW mannose-linked peptides. After identification, the NEPGCYF peptide showed the highest in silico blood-brain barrier penetrating property (B3Pred score: 0.70) and in silico free radical scavenger activity (FRS score: 0.54) among mannose-linked peptides. Molecular docking indicated that this peptide acted as competitive inhibitor for AChE and POP enzymes, and as non-competitive inhibitor for TYR enzyme. These mechanisms were confirmed by in vitro kinetic analysis using the inhibitory mannose-linked peptides and the synthetic peptide NEPGCYF. Purified mannoproteins from brewer's spent yeast are a promising source of bioaccessible glycosylated peptides with good neuroprotective and antioxidant properties.