Sea urchin gonads have been demonstrated to contain major yolk protein (MYP), which can be hydrolyzed by enzymes to release biologically active peptides. The in silico analysis of the MYP sequence in the BIOPEP database showed the presence of fragments with antioxidant activity. The sequence was hydrolyzed by 21 kinds of proteases and 23 antioxidant peptides were obtained. Eight peptides, including Leu-Trp (LW), Arg-Trp (RW), Ala-Trp (AW), Thr-Trp (TW), Ala-Asp-Phe (ADF), Leu-Trp-Lys (LWK), Ser-Asp-Phe (SDF) and Leu-Tyr (LY), were screened and a score over 0.5 was obtained using PeptideRanker. The peptides LW, TW and LWK showed a stronger antioxidant capacity with IC50 values of 8.85, 9.59 and 9.62 mmol L−1, respectively, compared to that of glutathione (10.81 mmol L−1). Furthermore, AW, LW and LY showed Trolox equivalent antioxidant capacity (TEAC) values of 3.07, 1.87 and 1.52 mmol TE per mmol peptide, respectively. These results suggest that the MYP from sea urchin (S. nudus) gonads is a good source of antioxidant peptides with abundant tryptophan.
The papain hydrolyzate prepared from purple sea urchin ( Strongylocentrotus nudus ) gonad exerts significant antioxidant activity. Through ultrafiltration, gel filtration and high performance liquid chromatography, the active fractions from the hydrolyzate were screened by alleviating paraquat-induced oxidative stress in Caenorhabditis elegans , and the peptide components were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Two antioxidant peptides SnP7 (AAVPSGASTGIYEALELR, 1805.03 Da) and SnP10 (NPLLEAFGNAK, 1173.34 Da) exhibit significant antioxidant capacity, which reduce reactive oxygen species (ROS) level and the expression of superoxide dismutase-3 (SOD-3) and heat shock protein-16.2 (HSP-16.2) in oxidation-damaged nematodes. Further studies indicated that SnP7 and SnP10 induce DAF-16 nuclear translocation and the expression of stress-related genes such as sod-3 . RNA interference (RNAi) suggested that peptide-induced enhancement of resistance is dependent on DAF-16. Taken together, S. nudus antioxidant peptides might act through activate DAF-16 signaling pathway, and induce the expression of DAF-16 target genes that enhance antioxidant potential of organisms.
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