Identification, In Silico Screening, Inhibition Mechanisms to Keap1 and Angiotensin-I-Converting Enzyme, and Ferrous-Transport Capacity of a Multifunctional Octapeptide from Camellia oleifera Globulin.

Camellia oleifera expeller is an abundant protein resource, but its usage in food is limited. In this study, potential antioxidant and hypotensive peptides with ferrous-chelating activity were isolated, identified, and virtually screened from camellia expeller globulin hydrolysates. The action mechanisms against Keap1 and angiotensin-I-converting enzyme (ACE), gastrointestinal stability, and ferrous-transmembrane absorption were studied. After in silico screening, a safe multifunctional octapeptide: Ser-Gly-Tyr-Gly-Tyr-Gly-Tyr-Gly (SGYGYGYG) was obtained. SGYGYGYG showed high ACE-restraining ability of IC₅₀:89.44 µmol/L (equivalent to that of Valsartan), ferrous chelating (8.67 mg/g) and hydroxyl radical quenching abilities (93.06%). SGYGYGYG can inhibit the Keap1-Nrf2 interaction by binding to 9 residues of Keap1; and it bound to key sites in ACE's linking (Tyr523, Gln281, Lys511, and Ala354) and catalytic centre (His353 and His383). SGYGYGYG's phenolic hydroxyl, amino, and carboxyl groups had strong affinity for ferrous ions. Ferrous chelation did not alter ACE-inhibition capacity and model of SGYGYGYG, but reduced its hydroxyl and ABTS radical quenching ability (p < 0.05). Moreover, the intestinal stability and transmembrane absorption of ferrous ions were improved by SGYGYGYG-ferrous chelate, though SGYGYGYG had poor gastrointestinal stability. Thus, SGYGYGYG may be exploited as ingredients of hypotensive, antioxidant, and iron supplementary agents.