ACE-Inhibitory Peptides Identified from Quinoa Bran Glutelin-2 Hydrolysates: In Silico Screening and Characterization, Inhibition Mechanisms of ACE, Coordination with Zinc Ions, and Stability.

To obtain Angiotensin-I-Converting Enzyme (ACE) inhibition peptides with Zn-chelating capacity, quinoa bran glutelin-2 hydrolysates (QBGH) by Flavourzyme and Papain were subjected to Sephadex G-15 gel chromatography, reverse phase-high liquid performance chromatography and UPLC-ESI-MS/MS analysis. Four oligopeptides including GGGSGH, EAGAE, AGGGAGGG and AVPKPS were identified. Of these, only the hexapeptide AVPKPS had both ACE-inhibitory activity (IC50: 123.13 μmol/L) and Zn-chelating ability (17.36 mg/g). Molecular docking showed AVPKPS could bind with active residues Glu384 and Ala354 (both belong to the central S1 pocket of ACE including) through short hydrogen bond and hydrophobic interactions, respectively. Inhibition kinetics verified that AVPKPS was a competitive inhibitor of ACE. Moreover, AVPKPS can affect the zinc tetrahedral coordination in ACE through binding with residues His387 and His383. Fourier-transform infrared spectroscopy analysis demonstrated that the amino and carboxyl groups of AVPKPS were the main chelating sites for zinc ions. Under the gastrointestinal digestion, the ACE inhibition capacity of AVPKPS was relatively stable, and the zinc solubility of AVPKPS-zinc complexes was more stable than zinc sulfate (p < 0.05). These results suggest that quinoa peptides have potential applications as ingredients for antihypertension or zinc fortification.