Isolation, identification, and structure-activity relationship of novel ACE inhibitory peptides from earthworm protein in vitro gastrointestinal digestion product

Earthworms are a good protein resources with several health-promoting effects, particularly for antihypertensive activity. However, the active components remain unknown. In the present study, earthworms’ protein in vitro gastrointestinal digestion product (EWP-GI) was prepared and purified by ultrafiltration and column chromatography. The potential angiotensin-converting enzyme (ACE) inhibitory peptides were identified using UPLC-MS/MS and screened using in silico tools and molecular docking. Finally, seven novel ACEI peptides (SSPLWER, RFFGP, LERWP, MFPGIADR, FPGIADR, SADRISHGF and ADRYSSWP) were obtained. The two most active peptides, SSPLWER and RFFGP, presented ACE inhibitory activity with IC50 values of 14.30 ± 0.81 and 117.63 ± 0.36 μM respectively, and both acted as competitive inhibitors. The peptides occupied the active sites of ACE to generate steric hindrance, which weakened the catalytic reaction. Moreover, the tryptophan residue in SSPLWER and the arginine residue in RFFGP played an important role in the ACE inhibitory effects of peptides. Thus, these results indicated that peptides were the active ingredients of earthworms that exerted ACE inhibitory activity after gastrointestinal digestion, offering a new perspective to further enlighten the hypotensive activity of earthworm.