Novel Antioxidant Peptides from Grateloupia livida Hydrolysates: Purification and Identification

Preparation, Isolation and Antioxidant Function of Peptides from a New Resource of Rumexpatientia L. ×Rumextianshanicus A. Los

Rumexpatientia L. ×Rumextianshanicus A. Los (RRL), known as "protein grass" in China, was recognized as a new food ingredient in 2021. However, the cultivation and product development of RRL are still at an early stage, and no peptide research has been reported. In this study, two novel antioxidant peptides, LKPPF and LPFRP, were purified and identified from RRL and applied to H2O2-induced HepG2 cells to investigate their antioxidant properties. It was shown that 121 peptides were identified by ultrafiltration, gel filtration chromatography, and LC-MS/MS, while computer simulation and molecular docking indicated that LKPPF and LPFRP may have strong antioxidant properties. Both peptides were not cytotoxic to HepG2 cells at low concentrations and promoted cell growth, which effectively reduced the production of intracellular ROS and MDA, and increased cell viability and the enzymatic activities of SOD, GSH-Px, and CAT. Therefore, LKPPF and LPFRP, two peptides, possess strong antioxidant activity, which provides a theoretical basis for their potential as food additives or functional food supplements, but still need to be further investigated through animal models as well as cellular pathways.

Purification, characterization, and in vitro digestion of novel antioxidant peptides from chicken blood hemoglobin

The study aimed to purify and characterize antioxidant peptides from chicken blood hemoglobin hydrolysate. The fraction M2  (< 3 KDa) with the strongest antioxidant activity was isolated by ultrafiltration, and its DPPH (1,1-diphenyl-2-picryl-hydrazyl radical) free radical scavenging rate, ABTS [2,2'-Azinobis-(3-ethylbenzthiazoline-6-sulphonate)] free radical scavenging rate, and iron ion chelation activity were 82.91%, 77.49%, and 80.99%, respectively. After in vitro digestion, the antioxidant capacity of chicken blood hydrolysate was significantly higher than that before digestion (p < 0.05). M2 exhibited the strongest antioxidant activity after stomach digestion, with a DPPH radical scavenging rate and iron ion chelating power of 82.91% and 79.61%, respectively. Component A was purified from M2 by Sephadex G-25 gel chromatography. The peptide sequences were identified by LC-MS/MS from fraction A, and four peptides, AEDKKLIQ (944.54 Da), APAPAAK (625.36 Da), LSDLHAHKL (1033.57 Da), and LSNLHAYNL (1044.54 Da) were synthesized using the solid-phase peptide method, among which APAPAAK was a novel antioxidant peptide. Molecular docking was used to simulate the binding of these four peptides to the key active site of Keap1 via hydrogen bonding. This study suggests that chicken blood may provide a new natural source of antioxidant peptides.

Purification and characterization of a novel immunoregulatory peptide from Sipunculus nudus L. protein

This study aimed to purify and characterize immunoregulatory peptides from Sipunculus nudus L. and to explore the underlying mechanisms. Ultrafiltration, gel filtration chromatography, and reverse phase high-performance liquid chromatography (RP-HPLC) were used to purify the peptide following enzymatic hydrolysis. Rates of lymphocyte proliferation and phagocytosis as well as nitric oxide (NO) production levels were used as indicators of immunoregulatory activity to screen the fractions. The amino acid sequence of the peptide, designated as SNLP, was identified as Arg-Val-Lys-Gly-Lys-Ile-Leu-Ala-Lys-Arg-Leu-Asn (RVKGKILAKRLN) by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Treatment with the synthetic SNLP increased the proliferation and phagocytosis of RAW 264.7 macrophages and promoted the secretion of tumor necrosis factor-ɑ (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β), and NO levels. The mRNA levels of these cytokines and iNOS were also increased by SNLP. Our results provide preliminary evidence suggesting that SNLP acts as a dual immunomodulatory peptide with immunostimulatory and anti-inflammatory activities. In summary, SNLP derived from Sipunculus nudus L. is a potent immunoregulatory peptide and represents a potential functional food or immunoregulatory drug.

Molecular Docking Revealed the Potential Anti-Oxidative Stress Mechanism of the Walnut Polypeptide on HT22 Cells

The preparation of novel antioxidant peptides from food raw materials is one of the research focuses, but there are fewer studies on the preparation of antioxidant peptides from walnut meal, a by-product of processing walnuts. This study analyzed the antioxidant properties and protective effects of walnut protein hydrolyzed by alkaline protease and trypsin on the oxidative stress of HT22 cells. The peptides were identified by UPLC-MS/MS, and the anti-oxidative peptides were screened based on virtual computer tools. The potential anti-oxidative stress mechanism of the walnut polypeptide on HT22 cells was explored by molecular docking. The results revealed that walnut protein hydrolysates (WPH) with molecular weights of less than 1 kDa had good antioxidant properties and inhibited oxidative damage of HT22 cells by regulating the levels of reactive oxygen species (ROS) and antioxidant enzyme catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px). Six of the ninety identified new peptides showed good solubility, non-toxicity, and bioactivity. The molecular docking results showed that the six peptides could dock with Keap1 successfully, and EYWNR and FQLPR (single-letter forms of peptide writing) could interact with the binding site of Nrf2 in the Keap1-Kelch structural domain through hydrogen bonds with strong binding forces. The results of this study provided important information on the antioxidant molecular mechanism of the walnut polypeptide and provided a basis for further development of walnut antioxidant polypeptide products.

Isolation and purification of antibacterial lipopeptides from Bacillus velezensis YA215 isolated from sea mangroves

The increasing burden and health risks of antimicrobial resistance (AMR) pose a great threat to society overall. Lipopeptides exhibit great potential as novel and safe alternatives to traditional antibiotics. In this study, the strain YA215, which was isolated from the mangrove area in Beibu Gulf, Guangxi, China, was identified as Bacillus velezensis. Then, YA215 lipopeptide extracts (YA215LE) from B. velezensis was found to exhibit a wide spectrum of antibacterial and antifungal activities. Additionally, YA215LE was identified and found to contain three groups of lipopeptides (surfactin, iturin, and fengycin). Furthermore, one separation fraction (BVYA1) with significant antibacterial activity was obtained. Additionally, liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis of BVYA1 showed three molecular ion peaks ([M + H]⁺: m/z 980.62; 994.66; 1008.66) corresponding to conventional surfactin homologs. By MS/MS analysis, BVYA1 was identified as sufactin with the precise amino acid sequence Glu-Leu/Ile-Leu-Val-Asp-Leu-Leu/Ile and hydroxyl fatty acids with 11-13 carbons. [M + H]⁺ at m/z 980.62 was detected for the first time in B. velezensis, which demonstrates that the strain corresponds to a new surfactin variant. In particular, BVYA1 showed antibacterial activity with the minimum inhibitory concentration (MIC) values of 7.5-15 μg/ml. Finally, the preliminary mechanism of inhibiting E. coli treated with BVYA1 showed that BVYA1 effectively permeabilized the cytoplasmic membrane and disrupted the morphology of targeted bacterial cells. In conclusion, this study suggests that the YA215LE from B. velezensis YA215 might be a potential candidate for a bactericide.

Purification, Identification and Molecular Docking of Immunomodulatory Peptides from the Heads of Litopenaeus vannamei

In order to realize the high-value utilization of Litopenaeus vannamei (L. vannamei) heads, immunomodulatory peptides were prepared from the enzymatic hydrolysate of L. vannamei heads, and the action mechanism of immunomodulatory peptides was determined by molecular docking. The results showed that six proteases were used to hydrolyze L. vannamei head proteins, with the animal protease hydrolysate exhibiting the highest macrophage relative proliferation rate (MRPR). The enzymatic products were then sequentially purified by ultrafiltration, Sephadex G-15 gel chromatography, identified by liquid chromatography-mass spectrometry (LC-MS/MS), and finally selected for six immunomodulatory peptides (PSPFPYFT, SAGFPEGF, GPQGPPGH, QGF, PGMR, and WQR). These peptides maintained good immune activity under heat treatment, pH treatment, and in vitro gastrointestinal digestion. Molecular docking analysis indicated that these peptides showed great binding to both toll-like receptor 2 and 4 (TLR2 and TLR4/MD-2), leading to immunomodulation. The discarded L. vannamei heads in this article are considered to be promising food-borne immunomodulators that contribute to enhancing the immune function of the body.