Identification of Structure-Linked Activity on Bioactive Peptides from Sea Cucumber (Stichopus japonicus): A Compressive In Silico/In Vitro Study

Background: A sea cucumber (Stichopus japonicus) is an invertebrate rich in high-quality protein peptides that inhabits the coastal seas around East Asian countries. Such bioactive peptides can be utilized in targeted disease therapies and practical applications in the nutraceutical industry.Methods: Bioactive peptides were isolated from Stichopus japonicus through ultrafiltration and Sephadex G-10 size exclusion chromatography. The low-molecular-weight fraction (ACSH-III) showed the highest hydroxyl radical scavenging and angiotensin-converting enzyme (ACE) inhibitory activities. Subsequent purification of ACSH-III resulted in four fractions, of which ACSH-III-F3 and ACSH-III-F4 exhibited significant bioactivity.Results: Peptides identified in these fractions, including Phenylalanine-Proline-Threonine-Tyrosine (FPTY) and Tyrosine-Proline-Serine-Tyrosine-Proline-Serine (YPSYPS), were characterized using high-performance liquid chromatography (HPLC) and quadrupole time-of-flight mass spectrometry (QTOF-MS). FPTY demonstrated the most potent antioxidant and antihypertensive activities among these peptides, with IC50 values of 0.11 +/- 0.01 mg/mL for hydroxyl radicals and 0.03 +/- 0.01 mg/mL for ACE inhibition. Docking simulations revealed strong binding affinities of these peptides to the active site of the ACE, with FPTY displaying interactions similar to those of the synthetic inhibitor lisinopril.Conclusions: These findings suggest that the identified peptides, particularly FPTY, have potential applications as natural antioxidants and functional foods.