Identification and molecular mechanism of novel antioxidant peptides from squid skin protein hydrolysates: In silico and in vitro analysis

Squid skin is rich in collagen and a high-quality source of bioactive peptides. This study aimed to identify novel antioxidant peptides derived from squid skin and to explore their potential molecular mechanism using in silico and in vitro approaches. Two novel peptides QDGFQGAH and SGDNLRFP were identified and demonstrated disparate of free radical scavenging and cytoprotective activities. Subsequent investigations exhibited that peptides were capable of reducing intracellular MDA level, and elevating the levels of antioxidant enzymes, including SOD, CAT, and GSH-Px. Furthermore, compared to the control, the expressions of Nrf2 treated with peptides were increased, while the levels of Keap1 were decreased, and the peptide QDGFQGAH showed the best activity. Molecular docking and dynamic simulations demonstrated that the peptides could form stable interactions with key residues of Keap1 by influencing the amino acid regions (Gly571-Asp589, Ala376-Cys395). Transport experiments on Caco-2 cell monolayers revealed that two novel peptides could traverse the intestinal epithelium. The findings suggest that the two peptides may be considered as potential antioxidant agents in functional foods, and provide a theoretical foundation for the extensive processing of squid skin.